I'm ready to roll this baby off the nearest cliff. 88GT with 5 spd, partial engine rebuild. I've got all the particulars in the Table below. Haven't worked on this since September but have been reading old posts, searching the net, etc. Asking for your help to fill out my Table ... I'm sure there are Factors that I've missed that might account for High NOx, but there is also reasoning behind some factors and how to test that are missing (or just plain wrong.) Anyway, I thought it would be useful for future Fiero Owners to have all of this gathered up into one Table. Please review and let me know what you think.
My plan is to work on the possible vacuum leak trouble shooting this weekend. After my 2nd test failure I DID find a disconnected hose and that helped for the September test but there might still be a smaller leak, so I'm going after that with two test methods.
Thanks in advance for all your help and thoughts!!
I'll just go with timing or EGR. I believe those are the 2 main causes of high NOX. Are you able to time the engine without any problems? There have been times when the balancer slipped and the timing is WAY off. Here is how the notches should line up:
Here's what happens when they slip:
[This message has been edited by IMSA GT (edited 02-11-2023).]
I would also put a scan tool on it and make sure that it is not running lean. The integrator can only adjust so much after that the engine runs lean for example if there is a vacuum leak.
Another thought would be dirty fuel injectors i.e. not all flowing equally. That could make a cylinder or two run lean even though overall the exhaust is on ratio. The lean cylinders could be making excess NOx.
------------------ formerly known as sanderson 1984 Quad 4 1886 SE 2.8L 1988 4.9L Cadillac 1988 3800 Supercharged
1 -- Cigar smoke test performed (after I stopped puking), hooking up to several different vacuum ports and also hoses, not even a hint of a leak. I'm a bit worried this might be a false negative due to not doing all possible ports/hoses.
2 -- Harmonic balancer checked (see picture below.) The HB has three slots, 2 thin, and 1 thick, and the thick one is indicated with the Red Arrow in the picture. It seems to be in approximately the right place although is not exactly like the diagram.
3 -- I don't have a scan tool. Is this an Autozone / O'Reilly's rental item perchance??
4 -- Now I'm just taking a moment to complain. When I went to jack the car up I was STUNNED to see brake fluid on the right, rear inside tire. This is one of my professionally rebuilt calipers, with <100 miles of use. There are two points where a drop form to drip down onto the rim, then the tire. I'm going to ignore this for now.
Yeah. High NOx is caused by high cylinder temperatures. Does it ping at all? It's almost guaranteed that if it pings, it's not going to pass. Ethanol (lots of it) is a good suggestion. It will cool off combustion temps. (I would suggest backing off the timing, but I think they check that for "on spec".) If your balancer ring has slipped (as above) it'll be impossible to time correctly.
Mine was failing due to a vacuum leak in the EGR circuit. In my case, it was at the rubber elbow that connects to the bottom of the throttle body. Check all the rubber vacuum fittings. They're very old now and can deteriorate, stretch, and leak.
3 -- I don't have a scan tool. Is this an Autozone / O'Reilly's rental item perchance??
I pretty sure that they don't lend out scan tools. They will read codes if you bring the car to them but you need to see what the short term fuel trim (integrator) is doing as the engine runs. Without a scan tool the other option is to datalog it with a lap top (or maybe Android phone) and a program such as WinALDL (free donwloads available). There may be cheaper options but here is one for $55 that gets you the necessary ALDL to USB cable, the software and I would think phone support if necessary:
Oh my, this is soooooo familiar! This could easily be my thread as my car has virtually the same problem. Even fails at low rpm on the rollers like his. Three fyi’s: The FieroStore used to sell an OBD1 scan tool but no more. Unless I missed it, I didn’t see any talk here about the computer. (I replaced mine but no change) I regularly Sea-Foam my car regularly- didn’t see any comments on this either.
Ok, I’ll shut up now cause I’m anxiously waiting for a fix to Notorio’s issue because I’m in the same exact boat. Kit P.S. Recently changed caliper? I can’t begin to tell you how many times I had brake fluid leaks at the banjo fitting on the caliper. If that is where the leak is, I can almost guarantee you it’s the copper / aluminum crush washers. (copper is better in my opinion) Anyways, always use NEW ones and make sure they are the proper size and diameter. Ones that fit snugly around the banjo bolt are your best bet.
[This message has been edited by Kitskaboodle (edited 02-13-2023).]
4 -- Now I'm just taking a moment to complain. When I went to jack the car up I was STUNNED to see brake fluid on the right, rear inside tire. This is one of my professionally rebuilt calipers, with <100 miles of use. There are two points where a drop form to drip down onto the rim, then the tire. I'm going to ignore this for now.
There's a rubber seal under the parking brake lever. I'd try replacing that and putting some silicone grease on it.
------------------ formerly known as sanderson 1984 Quad 4 1886 SE 2.8L 1988 4.9L Cadillac 1988 3800 Supercharged
There's a rubber seal under the parking brake lever. I'd try replacing that and putting some silicone grease on it.
I'll check that out! It gives me hope I won't have to remove and ship back to the rebuilder
Kit, I am bummed to hear you are STILL failing smog. My registration is in the strange, Twilight Zone where it is 'incomplete,' which means even though a year has come and gone the DMV didn't send me out a registration form for 2023. So when I eventually go to the DMV (by the way, none of the ones in my area are accepting appointments now ) I will have fines. The on-line status shows my car as 'non-Op' but I paid a sh--load of money last year to get it back into active status.
Trying to catch up with suggestions: I should have mentioned that the fuel injectors were professionally serviced, although one died and had to be replaced (to solve a regular, misfire issue.)
Haven't attempted the shop-vac trial yet or using the EGR trouble-shooting table from the FSM. An issue is that I have the New Style of EGR that makes it impossible to SEE if the valve is actuating or not.
And thanks for the suggestion on the scan tool. Looks very useful and not too expensive.
[This message has been edited by Notorio (edited 02-13-2023).]
First a very basic test of the EGR valve itself - if you reach underneath it you can push up on the diaphragm and force it open. If you do that, the engine should stumble. That doesn't tell you if vacuum is actually pulling it open in operation though.
Since you cleared (visual) inspection I guess you don't have a code 32 showing? I'm surprised - that's the notorious EGR trouble code that people usually get. The EGR solenoid is notoriously failure prone, and I'm not sure the ECM can detect all of the solenoid's failure modes. I wonder if there's a good way to test the solenoid for functionality. Unfortunately they are unique to the Fiero and CA is very inflexible about non-original parts, so the factory solenoid is too "special" and expensive to replace without a really solid diagnosis that it's needed. There is an old thread here from BuddyCraigg about how to rebuild that solenoid, and might have also had some testing methods.
Retarding the timing should reduce N2O - but they check that to be within an allowed tolerance of factory spec. If you get desperate, and are able to mess with tuning your own chip - if you retard the timing at the chip then it won't show up in an inspection. They don't plug into the ECM on an OBD1 era car. Otherwise, you have a small amount of wiggle room to change the distributor timing. On my tests the spec was always +/- 3 degrees, but I remember people on here insisting it was 2 or something. Maybe it depends where you live. Your test report should say what the allowed tolerance is and where they think it was when they checked it. Unfortunately reading the timing on these cars seems to be pretty fuzzy and subjective due to parallax and poor visibility in general. I also had a shaky timing mark (maybe yours is better). You could probably take 1 degree out at least without much chance of getting failed for it.
This is an awfully dumb idea: but if EGR isn't opening properly, I wonder if a controlled leak of EGR would work at all. Maybe there's a sweet spot where it will still idle, be driveable but also pass the test. Who knows where that would be, though. Too much EGR and the misfiring would cause higher unburned fuel (HC).
I don't think your new catalyst is an issue, and I doubt the imperfections of your idle are much of a factor either. My car has always had an unsteadiness and occasional miss at idle. I think it's just the way these cars run, the ECM isn't good enough to idle any better than that. My catalyst was brand new in 2012 and it's HC and CO readings were near zero even though I heard it stumble very badly during the 2500rpm test. (there was a tuning issue with my non-original injectors that I had not yet figured out) I was never tested for N2O though. I lived in a rural area so I took the "two speed idle" test which doesn't measure N2O. It was still passing (but not as easily) in 2020, still a bit unsteady and prone to sporadic misfire as it's always been.
[This message has been edited by armos (edited 03-06-2023).]
Recently changed caliper? I can’t begin to tell you how many times I had brake fluid leaks at the banjo fitting on the caliper. If that is where the leak is, I can almost guarantee you it’s the copper / aluminum crush washers. (copper is better in my opinion) Anyways, always use NEW ones and make sure they are the proper size and diameter. Ones that fit snugly around the banjo bolt are your best bet.
New copper washers are not necessary!
quote
Originally posted by Marvin McInnis:
Yes, copper crush washers can be reused, but they must be annealed first. New copper crush washers should already be in the annealed condition, so you normally should be able to use them right out of the box. (Copper will slowly age-harden at room temperature, though. Those copper crush washers you bought 10 years ago, even though "new," may need to be annealed before use.) When you install them the crushing process work-hardens the copper, so they become much less flexible and may not seal if you try to reuse them "as is." Heating the copper washers to annealing temperature (~1100 degrees F ... a simple propane torch will do) and cooling them back to room temperature will restore their ductility and allow them to be reused once or twice.
Soft aluminum crush washers work-harden when used, too, but they can't reliably be annealed using simple workshop tools and techniques. Just throw them away and buy new ones. I assume that the use of aluminum crush washers is becoming more common due to the increasing price of copper.
Yes, copper crush washers can be reused, but they must be annealed first. New copper crush washers should already be in the annealed condition, so you normally should be able to use them right out of the box. (Copper will slowly age-harden at room temperature, though. Those copper crush washers you bought 10 years ago, even though "new," may need to be annealed before use.) When you install them the crushing process work-hardens the copper, so they become much less flexible and may not seal if you try to reuse them "as is." Heating the copper washers to annealing temperature (~1100 degrees F ... a simple propane torch will do) and cooling them back to room temperature will restore their ductility and allow them to be reused once or twice.
Soft aluminum crush washers work-harden when used, too, but they can't reliably be annealed using simple workshop tools and techniques. Just throw them away and buy new ones. I assume that the use of aluminum crush washers is becoming more common due to the increasing price of copper.
[/QUOTE]
New copper washers are dirt cheap. It makes no sense to anneal used washers
------------------ formerly known as sanderson 1984 Quad 4 1886 SE 2.8L 1988 4.9L Cadillac 1988 3800 Supercharged
New copper washers are dirt cheap. It makes no sense to anneal used washers.
Even if copper washers were free (which they're not), it makes more sense to me to avoid the nuisance of chasing down new parts if I can spend two minutes with a propane torch to totally revitalize the copper washers I already posses.
I haven't done a lot of brake work, but I've never had a caliper banjo bolt leak during the 50 years I've been servicing my own vehicles.
[This message has been edited by Patrick (edited 03-06-2023).]
Update on leak ... I want to fix this so I can put the car back on the floor to finish the EGR etc. troubleshooting.
First Image: This is where the leak is coming from. The banjo and the bleeder are not leaking. The bracket has been removed for this picture.
Second Image: This is how the stack goes together. There is a rubber 'washer' type unit and then the very thin plastic ring and you can see where they go. I guess I'm surprised that the plastic ring is not a leak path at all times. Is this really how this is supposed to be? Meanwhile, I'll tottle down to O'Reilly's and see what they have to replace the somewhat beat-up-looking rubber washer.
Looks like Rockauto has a rear caliper rebuild kit for less than $10.
I looked at an exploded picture of the caliper and there is an o-ring seal on the inside that keeps brake liquid from coming out. I'm now thinking that the outside seal inside the lever is to keep water from getting in and causing corrosion of the shaft. The piston needs to be removed to look at the inside o-ring seal.
------------------ formerly known as sanderson 1984 Quad 4 1886 SE 2.8L 1988 4.9L Cadillac 1988 3800 Supercharged
Looks like Rockauto has a rear caliper rebuild kit for less than $10.
I looked at an exploded picture of the caliper and there is an o-ring seal on the inside that keeps brake liquid from coming out. I'm now thinking that the outside seal inside the lever is to keep water from getting in and causing corrosion of the shaft. The piston needs to be removed to look at the inside o-ring seal.
Doh, I just finished replacing that outer rubber washer with a viton o-ring that is somewhat thicker. If it continues to leak I'll contact calipersonline and perhaps they will send me the inside seal, since the calipers have <100 miles on them. In the meantime I can move the car again and get back to the High NOx issue
Kit, I think I'm onto something. Here is the EGR data as a result of (trying to) follow the confusing Field Service Manual's flowchart. It boils down to:
1) does the EGR Solenoid open around 1800 rpm 2) does the vacuum applied to the EGR Valve exceed 2" of Hg (and is it less than 10".)
The vacuum gauge that I have is VERY hard to read below perhaps 4". I did multiple measurements and MOSTLY have convinced myself that the EGR Solenoid DOES work, that the lines from the Throttle Body to the Solenoid to the Valve DO NOT leak, however, the vacuum the EGR sees is marginally LESS than what will open the valve using a manual pump. i.e. the 2" reading that I think I see at the Valve is less than the 3" the Valve needs to open. If I apply the alleged 2" with a manual pump the valve stays closed. At about 3" the valve opens the the IDLE starts to stumble.
Referring to the diagram below, I started my measurements at A but worked myself back to D to test for leaks in the vacuum circuit. The reading is the SAME at A, B, C, and D. If there is a drop-off, the gauge is too insensitive to pick it up. Anyway, I think the question is now HOW do I increase the ported vacuum from the Throttle Body to something more like 4-5"??
p.s. I MIGHT just fashion myself a Water Manometer so I can see very clearly if the System Vacuum really is sufficient to open the EGR Valve.
[This message has been edited by Notorio (edited 03-12-2023).]
2) cracked EGR tube allowing air to enter with EGR gases causing lean condtion
2) small leak in diaphragm of ECR valve causing reduced opening at a given vacuum
3) wrong EGR valve there are three types; negative back pressure, positive back pressure and port. The numbers on the valve should be formatted like:
CBT 17083821 34121
There should be no N or P after 34121 (date built). This indicates the correct port type valve 17083821 is the part number
Since you do not have a code 32 the EGR is likely seeing at least 2" of vacuum with EGR commanded on.
EGR is commanded on at 1200 rpm and MAP's less than 60 kPa. However the duty cycle is not large 11.7 % to 19.5% depended in MAP so normal vaccum to EGR valve may not be that high.
------------------ formerly known as sanderson 1984 Quad 4 1886 SE 2.8L 1988 4.9L Cadillac 1988 3800 Supercharged
Kit, I think I'm onto something. Here is the EGR data as a result of (trying to) follow the confusing Field Service Manual's flowchart. It boils down to:
1) does the EGR Solenoid open around 1800 rpm 2) does the vacuum applied to the EGR Valve exceed 2" of Hg (and is it less than 10".)
The vacuum gauge that I have is VERY hard to read below perhaps 4". I did multiple measurements and MOSTLY have convinced myself that the EGR Solenoid DOES work, that the lines from the Throttle Body to the Solenoid to the Valve DO NOT leak, however, the vacuum the EGR sees is marginally LESS than what will open the valve using a manual pump. i.e. the 2" reading that I think I see at the Valve is less than the 3" the Valve needs to open. If I apply the alleged 2" with a manual pump the valve stays closed. At about 3" the valve opens the the IDLE starts to stumble.
Referring to the diagram below, I started my measurements at A but worked myself back to D to test for leaks in the vacuum circuit. The reading is the SAME at A, B, C, and D. If there is a drop-off, the gauge is too insensitive to pick it up. Anyway, I think the question is now HOW do I increase the ported vacuum from the Throttle Body to something more like 4-5"??
p.s. I MIGHT just fashion myself a Water Manometer so I can see very clearly if the System Vacuum really is sufficient to open the EGR Valve.
What you are concluding is exactly what I had concluded: that despite all systems checking ok (vacuum lines & elbow integrity, egr solenoid, egr valve, throttle body lines, etc.) the egr valve must NOT be getting enough ported vacuum to open properly or enough. As you did, i was able to fully open my egr valve doing a manual test with my Mighty Mite vacuum tester but as I recall, I remember having to apply a good 4-5 hg’s to get it to open properly. Kit
EGR is commanded on at 1200 rpm and MAP's less than 60 kPa. However the duty cycle is not large 11.7 % to 19.5% depended in MAP so normal vaccum to EGR valve may not be that high.
Appreciate you thinking about this issue. On Friday I should be able to get back to Fiero trouble-shooting. I'll definitely check on that possible restriction. Also posting next steps in response to Kit.
BUT, where do you find the 1200 rpm number? My 88 service manual says 1800 rpm and 2" Hg.
What you are concluding is exactly what I had concluded: that despite all systems checking ok (vacuum lines & elbow integrity, egr solenoid, egr valve, throttle body lines, etc.) the egr valve must NOT be getting enough ported vacuum to open properly or enough. As you did, i was able to fully open my egr valve doing a manual test with my Mighty Mite vacuum tester but as I recall, I remember having to apply a good 4-5 hg’s to get it to open properly. Kit
I am in good company then! (Misery loves company, right??)
Friday I should be able to get back to this. I recalled I had a spare Throttle Body so I got that out and was quite surprised to see that the ported vacuum path for the small EGR nipple and the large Purge nipple are exactly the same. I haven't measured the tiny, pin-point openings in the TB but they sure LOOK the same to me. Anyway, Friday I will measure the vacuum at BOTH nipples, to see how they compare.
If there are no clogs or restrictions, my seat-of-the-pants idea was to enlarge the diameter of the hole in the TB, by say, 50%. Thoughts on this?? Another option would be to drill out the EGR nipple and replace with larger diameter. This being UNDER the TB perhaps it wouldn't fail visual inspection.
FWIW, I have fought this battle before. Problem ended up being the rubber elbow that plugged on to the throttle body port. The end where the plastic hardline plugged in was deteriorated. But you've already looked at that, so...
One thing I thought about, in the middle of it all, was just running a hose from the TB port, up under the plenum, and straight back to the EGR valve, bypassing the solenoid. But that will allow the code to set, unless you "tee in" the switch on the solenoid. That should provide plenty of EGR, provided the engine doesn't misfire. It's a crapshoot, though.
Over the years, some people have dumped a bunch of Naptha into their tank.
[This message has been edited by Raydar (edited 03-14-2023).]
I have Tunercat and I looked at the AKYN broadcast code EPROM calibration for an 88 Fiero. EGR is commanded at 1200 rpm.
Hmmmn, don't know what to make of that. Does this show an increasing Voltage to the EGR Solenoid, say just becomes non-zero at 1200 rpm and ramps up to X at 1800 rpm and higher?
FWIW, I have fought this battle before. Problem ended up being the rubber elbow that plugged on to the throttle body port. The end where the plastic hardline plugged in was deteriorated. But you've already looked at that, so...
One thing I thought about, in the middle of it all, was just running a hose from the TB port, up under the plenum, and straight back to the EGR valve, bypassing the solenoid. But that will allow the code to set, unless you "tee in" the switch on the solenoid. That should provide plenty of EGR, provided the engine doesn't misfire. It's a crapshoot, though.
Over the years, some people have dumped a bunch of Naptha into their tank.
Maybe you didn't see that I measured the vacuum at the TB port and it is no higher than what arrives via the whole circuit (through the solenoid.) I'm hoping there is build-up in the TB part of the circuit, which I'll try to ascertain on Friday (i.e. lots of TB cleaner and high-pressure air). While I'm playing with that I'll also try your Direct Hose suggestion.
re: additives, I'm going to go with a gallon of Ethanol added to the tank, unless somebody knows why that would be detrimental ...
Originally posted by Notorio: Hmmmn, don't know what to make of that. Does this show an increasing Voltage to the EGR Solenoid, say just becomes non-zero at 1200 rpm and ramps up to X at 1800 rpm and higher?
The EGR solenoid is controlled by pulse width modulation. The EGR solenoid is supplied with 12V. The ECM grounds the EGR solenoid to energize it it many times per second. The on-time of the pulses determines how much vacuum the EGR valve will see. I believe an oscilliscope would be necessary to see the actual milisecond pulse width.
As shown below, there is a table in the PROM that shows % EGR vs MAP (kPa) vs RPM.
The top row is kPa. The first column is RPM. Sorry the formatting is screwed up. PFF doesn't like tables ------------------ formerly known as sanderson 1984 Quad 4 1886 SE 2.8L 1988 4.9L Cadillac 1988 3800 Supercharged
[This message has been edited by sanderson231 (edited 03-14-2023).]
I'm ready to roll this baby off the nearest cliff.
You could just roll it into a state with more reasonable emissions
Only advice I can give is that when I use the search function on the forum, there are a lot of threads where people had high NOx. A lot of people solved their problem and the threads give a lot of ideas how.
One of my Fieros had high NOx the last year it had to pass inspection and I solved it just by driving the car for an hour before getting to the inspection place. My problem was my birthday is in winter and I was driving to the closest emissions place and didn't give the car time to warm up properly. Also if they're doing it in the wrong gear or something take it to a different shop.
The EGR solenoid is controlled by pulse width modulation. The EGR solenoid is supplied with 12V. The ECM grounds the EGR solenoid to energize it it many times per second. The on-time of the pulses determines how much vacuum the EGR valve will see. I believe an oscilliscope would be necessary to see the actual milisecond pulse width.
As shown below, there is a table in the PROM that shows % EGR vs MAP (kPa) vs RPM.
Important Update: so I bought a vacuum gauge with more resolution on the low end (see below.) The RED arrow shows vacuum on the Throttle Body's EGR Solenoid port at 1800 rpm is barely 1" Hg. The GREEN arrow shows where the 2" reading is and it takes about 3000 rpm to hit that value. Please also note, the larger Purge port has the exact same readings as the EGR port, namely, around 1" at 1800 rpm and 2" around 3000 rpm. This means both ports are limited by the identical TB orifice size (which is what I was thinking HAS to be the case), and both are probably more or less clogged to the same degree. NEXT STEP is to remove the TB and clean the ports ...
Maybe you didn't see that I measured the vacuum at the TB port and it is no higher than what arrives via the whole circuit (through the solenoid.)
Yup. That's why I said, "I know you checked that..."
Just threw it out there since nothing else seemed to be making sense, either.
Do you have a hand operated vacuum pump? Maybe try connecting it straight to the EGR valve, while the engine is running, and see how much vacuum it takes before the engine notices the valve is open. Any change would be a positive thing. You don't necessarily have to stall the engine.
[This message has been edited by Raydar (edited 03-18-2023).]
Yup. That's why I said, "I know you checked that..."
Just threw it out there since nothing else seemed to be making sense, either.
Do you have a hand operated vacuum pump? Maybe try connecting it straight to the EGR valve, while the engine is running, and see how much vacuum it takes before the engine notices the valve is open. Any change would be a positive thing. You don't necessarily have to stall the engine.
I'm happy to report that I did that too: the reading on the crummy gauge on the hand pump needed to open the EGR and cause idle to stumble was higher than the EGR port was putting out. This is why I was starting to suspect that the vacuum originating on the TB ports was marginal to effectively open the EGR.
Report on cleaning the vacuum circuit and the little holes: they were barely dirty at all. Were dirty enough to produce the low-vacuum readings?? I'm more suspicious of the TB base gasket leaking.
So THIS is interesting. Those two little holes drilled into the TB are actually angled DOWN toward the base of the TB (away from the plate) and INWARD toward each other. Below are two pics to illustrate. Since the holes are angled it looks like my tiny Dremel drill chuck would fit in there nicely, if I had the appropriate sized bit.
The first one shows the overall angle with a paper clip that is too skinny for the hole. The angle it shows is therefore a bit exaggerated.
The second one shows the holes filled with two little taper pins I have from working on clocks. I was able to draw a line where they stop on the hole and then remove and measure the size of the orifices: both are the same, 0.058 ".
[This message has been edited by Notorio (edited 03-18-2023).]
Important Update: so I bought a vacuum gauge with more resolution on the low end (see below.) The RED arrow shows vacuum on the Throttle Body's EGR Solenoid port at 1800 rpm is barely 1" Hg. The GREEN arrow shows where the 2" reading is and it takes about 3000 rpm to hit that value. Please also note, the larger Purge port has the exact same readings as the EGR port, namely, around 1" at 1800 rpm and 2" around 3000 rpm. This means both ports are limited by the identical TB orifice size (which is what I was thinking HAS to be the case), and both are probably more or less clogged to the same degree. NEXT STEP is to remove the TB and clean the ports ...
So you connected a vacuum gauge directly to the port on the throttle body for the EGR, are sure that the hose had no leaks and got 1" Hg vacuum at 1800 rpm? As long as there are no leaks in the hose the size of the hole in the TB does not matter because there is no flow in the hose therefore no pressure drop.
I don't have a running 2.8L to compare to. I do have a 2.8L engine in the garage and the port for the EGR looks like it is downstream of the butterfly where there should be plenty of vacuum at idle. I do have a running 4.9L where the EGR port is definitely downstream of the butterfly on the TB. I hooked a vac gauge directly to that port and got 22" Hg vacuum with two different gauges at 1000 rpm. How much vacuum do you have at the connection on the upper intake for the MAP sensor? Something is not making sense.
------------------ formerly known as sanderson 1984 Quad 4 1886 SE 2.8L 1988 4.9L Cadillac 1988 3800 Supercharged
I keep on thinking about this. Do you have an "overbored" throttle body? I seem to remember having "low vacuum" on my modded throttle body, when I was having EGR issues. I don't remember if I changed the throttle body, or if I was just mistaken. (Sorry. Again, one of those "hmmmm..." things.)
But... The EGR port on the TB is not "full vacuum". It's ported vacuum. IOW, it won't show much vacuum with the throttle closed, OR at WOT. It's just at part throttle. And that's where you want the EGR to work.
[This message has been edited by Raydar (edited 03-18-2023).]
I keep on thinking about this. Do you have an "overbored" throttle body? I seem to remember having "low vacuum" on my modded throttle body, when I was having EGR issues. I don't remember if I changed the throttle body, or if I was just mistaken. (Sorry. Again, one of those "hmmmm..." things.)
But... The EGR port on the TB is not "full vacuum". It's ported vacuum. IOW, it won't show much vacuum with the throttle closed, OR at WOT. It's just at part throttle. And that's where you want the EGR to work.
Very interesting thought. No, both of the TB I have are stock. Ported -- right. The vacuum results from the airflow across the two holes, which changes as the TB opens. The service manual says this should be in the range of 2 - 10" of Hg for the EGR to work properly, when measured at 1800 rpm. With the TB at idle, essentially closed, there is no vacuum on the two ports.
Here are the results of Cleaning the TB, assuring the vacuum circuits are completely OPEN, and reinstalling the TB with a new gasket and gasket sealer. Drum roll .... NO CHANGE in the measured vacuums. Dang, I thought for the sake of Posterity, I had better do this FIRST, before proceeding to the irreversible step of enlarging the orifices.
Oh, BTW, I broke off the rubber vacuum end on the vacuum line going to the EGR solenoid. Yes, I'm fit to be tied
Important Update: so I bought a vacuum gauge with more resolution on the low end (see below.) The RED arrow shows vacuum on the Throttle Body's EGR Solenoid port at 1800 rpm is barely 1" Hg. The GREEN arrow shows where the 2" reading is and it takes about 3000 rpm to hit that value...
NEXT STEP is to remove the TB and clean the ports ...
We went over all this in Kits thread, and you even "seconded" my conclusion, that these vacuum gauges are simply not accurate enough to measure such low vacuum. The vacuum gauge you used has less resolution than mine, and mine doesn't appear to be accurate enough... so be careful about what conclusions you may have surmised regarding "clogged" ports.
I've just come in after "T"ing my Mityvac II into the EGR vacuum line (at the valve) of my Formula. At idle, there was no discernible vacuum, as was expected. When I revved the engine (and the EGR solenoid activated), the vacuum went to a steady 2 inHg (on a scale that goes up to 30 inHg).
However...
Even though I was using my most "accurate" vacuum gauge (it has the finest graduation of the three gauges I own), I don't know how much credence can be given to my (or any of our) readings. IMO, these gauges are far too basic/inaccurate to be measuring such a low vacuum with any precision.
Given that the vacuum source is ported the vacuum will depend on the position of the butterfly. The butterfly position while revving the engine to 1800 rpm in neutral vs driving down the road with the engine at 1800 rpm will be different The factory service manual does say when doing the 1800 rpm test to "have the engine in drive (automatic transmission), hold brake, accelerate momentarily to 1800 rpm and observe gauge". I'd suggest hooking a gauge with a long hose to the EGR port on the TB and taking the car for a drive while observing the gauge.
If it passes an 1800 rpm test, I would remove the top intake to inspect the EGR tube and where it enters the tube attaches to intake manifold to make sure that it is not grimed up.
Still curious that GM used ported vacuum when the ECM is using pulse width modulation to control the EGR solenoid)
------------------ formerly known as sanderson 1984 Quad 4 1886 SE 2.8L 1988 4.9L Cadillac 1988 3800 Supercharged
There are two points where a drop form to drip down onto the rim, then the tire. I'm going to ignore this for now.
