I had a bit of time last night and I don't understand why the engine is behaving this way: started engine, computer did its idle adjust thing. When idle settled down I had to advance timing to get it to run smooth. Jumpered A&B (no check engine light) and set timing to about 13°. Pulled jumper and engine immediately died. What am I missing?
I had a bit of time last night and I don't understand why the engine is behaving this way: started engine, computer did its idle adjust thing. When idle settled down I had to advance timing to get it to run smooth. Jumpered A&B (no check engine light) and set timing to about 13°. Pulled jumper and engine immediately died. What am I missing?
The jumper places the ECM in open loop mode. When you remove it the ECM goes into closed loop mode and seeks all of the sensor inputs to function but it takes a drive to about 40 mph to reset properly. Start engine and drive it, then see what happens.
------------------ " THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite. "THE COLUSSUS" 87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H " ON THE LOOSE WITHOUT THE JUICE "
I do need to ask where do I start? Set timing with jumper 1st or set timing by ear (without jumper)?
If you could write up a step by step procedure that would be a tremendous help. I have never been able to find that in all of the research that I have done. Apparently GOOGLE does NOT know everything
Just a point of information. Both my 92 and 93 factory service manuals recommend 10 degree base timing. This is what I run in both of my 4.9 cars. In the automatic car any more timing induces significant spark knock under load; The manual transmission seems more forgiving tolerating 12 degrees without knock. Both have RockCrawl chips in the ECM which adds timing advance throughout the engines operating range when in closed loop.
Rolland
[This message has been edited by 87convert (edited 08-31-2021).]
Racer37 has allowed me to move the Formula to someone who is familiar with Fieros and some of the engine transplants. This was to get a fresh view of the situation from an outsider. He is not a member of PFF and has asked me to be an intermediary to post questions from him. He isn't registered here and doesn't desire to. At the present time, only he and I know the location of the 4.9 Formula. He will read any comments and suggestions posted here.
This is what he sent me for posting. I will just give him the username of Troubleshooter.
Heading: 4.9 runs smoothly with A-B jumpered, rough without
I'm working on a Fiero with a 4.9 Cadillac engine. It runs smooth when the A and B terminals on the ALDL connector are jumpered, and very rough without the jumper. I found a thread on Pennock's that describes the same problem: https://www.fiero.nl/forum/...060811-2-068938.html But his solution, a new ignition coil, does not fix the problem on this car. Another symptom I have observed is that, without the jumper, cylinder one fires regularly on the timing light. But I tried it on cylinder 8, and it fires very irregularly. I would like replies from people who have experienced this problem and found a fix. Please do not reply with lessons on timing or firing order. I assure you that these are correct in this case.
[This message has been edited by fierofool (edited 09-16-2021).]
Watching. I thought this was no longer an issue. Did the chip/memcal help? To be honest, other than VATS and some trouble codes being turned off, and a bump in the idle speed, it really shouldn't make much of a difference. ("It didn't." is an acceptable response.)
Please let me know if I can do anything. Since "Troubleshooter" is on it, I'll be quiet, and won't offer any suggestions that may derail his thought process. But I have a set of manuals, and some other resources, available. Please don't hesitate to ask.
[This message has been edited by Raydar (edited 09-17-2021).]
Racer37 has allowed me to move the Formula to someone who is familiar with Fieros and some of the engine transplants. This was to get a fresh view of the situation from an outsider. He is not a member of PFF and has asked me to be an intermediary to post questions from him. He isn't registered here and doesn't desire to. At the present time, only he and I know the location of the 4.9 Formula. He will read any comments and suggestions posted here.
This is what he sent me for posting. I will just give him the username of Troubleshooter.
Heading: 4.9 runs smoothly with A-B jumpered, rough without
That's a timing issue as with A-B jumped the computer isn't adding any timing advance.
quote
I'm working on a Fiero with a 4.9 Cadillac engine. It runs smooth when the A and B terminals on the ALDL connector are jumpered, and very rough without the jumper. I found a thread on Pennock's that describes the same problem: https://www.fiero.nl/forum/...060811-2-068938.html But his solution, a new ignition coil, does not fix the problem on this car. Another symptom I have observed is that, without the jumper, cylinder one fires regularly on the timing light. But I tried it on cylinder 8, and it fires very irregularly. I would like replies from people who have experienced this problem and found a fix. Please do not reply with lessons on timing or firing order. I assure you that these are correct in this case.
So the other possibilities are a bad spark plug or plug-wire on # 8 and you should probably check the others as well...
He had told me he replaced the spark plug wire with one he had from another car and it made no difference. That was why he replaced the ignition coil.
It seems to be something operating "right on the ragged edge", that is stressed by the timing advance being added. All that are left (ignition-wise) are the distributor cap (the #8 terminal, specifically - I would look for carbon tracks) and the spark plug. Pretty much everything else is "common" to the entire system.
It there a possibility that the engine has jumped time?
That was one of my guesses as well but I also thought that a rocker arm retainer bolt might have stripped out of the aluminum support and changed the valve timing on two valves. That is often a problem on the HT v8 engines.
------------------ " THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite. "THE COLUSSUS" 87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H " ON THE LOOSE WITHOUT THE JUICE "
The timing was verified by Racer37 and a couple of others several times. It was rechecked after I delivered it to Troubleshooter. The timing is correct.
I think this has to be an electrical issue. The jumper wire won't fix a pulled rocker stud. It won't fix a bad distributor cap terminal or remove carbon tracking. Other than taking the sensors out of the picture, what circuits going to the ECM change with and without AB jumpered?
If one sensor at a time were unplugged, might that reveal the problem area? It's like one of the sensors is giving some incorrect info to the ECM.
The timing was verified by Racer37 and a couple of others several times. It was rechecked after I delivered it to Troubleshooter. The timing is correct.
Is the 4.9 like the Fiero 2.8 where a slipped harmonic balancer causes incorrect timing readings?
I think a slipped balancer could be common on most cars. Aren't most outer rings mounted on a rubber cushion? The scanner was showing 25* last setting I was told about. I think Troubleshooter only used the timing light to check for firing on each wire. I'll send him a message about the plugs. But if a wire or plug is bad, the ALDL jumper wouldn't cure that problem. It would still run rough.
I used an oscilloscope to check some things. I checked with the engine running with A-B jumpered, and then pulled the jumper out to see if there was any difference. Here's what I checked. Distributor Reference (pin D8 on the PCM). This is a crank position signal, and should be a regular square wave with 8 pulses for every crank rotation. This signal is supplied to the PCM by the distributor. It looked OK for both cases, considering that the frequency wasn't steady as the engine sputtered with the jumper out.
Electronic Spark Timing (pin C8 on the PCM). This is supposed to be like the crank signal, but advanced or retarded as required by the engine. This signal is supplied to the distributor by the PCM. This also looked normal. Of course, I couldn't tell if it was advanced or retarded.
Cam Position Sensor (pin C5 on the PCM). According to the manual, this is supposed to be one pulse for each time the intake valve for cylinder one is about to open. This signal is supplied to the PCM by the distributor. This also looked normal, but there's no way I could tell if it was in the right place. The belt was thrown when I pulled the jumper in this test, so that's all I did for now.
There is another line, Bypass (C7 on the PCM), controls whether the ICM uses the EST signal or the signal directly from the pickup coil to trigger the spark coil. I need to measure that line with the jumper in and out to see if that is the mechanism for using fixed park with A-B jumpered. If so, that would mean that the PCM is doing nothing at all with A-B jumpered, as far as ignition goes.
But the belt was thrown when I pulled the jumper in the Cam Position test, so that's all I did for now.
I got an email this morning from Troubleshooter. Anybody in the Northern half of Georgia have a Dual-Trace oscilloscope that I could borrow for a while?
From Troubleshooter:
If I had a dual trace oscilloscope, I could compare traces, to see if the EST signal is advanced or retarded compared to the crank signal, and I could compare the cam signal to the crank signal, to see if there is one pulse for every 16 crank pulses. But I don't have one, and they are expensive. I wonder if any of your members has a dual trace oscilloscope.
Having been a Fiero owner for over 20 years I knew that. This case is a cadillac ecm and doesn't work that way since it is designed to use the hvac display to show codes
Another clue: Charlie has some videos that I sent him showing how the car runs with and without the jumper. You can adjust the rough running out of it by retarding(?) the distributor. Turn the distributor counterclockwise about 20-25° and it runs smoother.
I will agree that it is something in the timing circuit, or rather something in the wiring for the timing circuit. I say wiring since this behavior doesn't change when the ecm is changed. There should be another ecm in the car to verify.
Also need to say that everything in the ignition system except the plug wires are new. The plug wires passed testing with a DVM. Spark plugs are new gapped at .060. New cap, rotor button, ICM, cam sensor,
Static timing has been checked, rechecked, re rechecked, and re re re reverified. Timing chain is good. Compression is good, 15# difference between highest & lowest.
There is a red paint marker line on the balancer to verify it has not slipped.
Today I found that the Bypass signal is always high, which means that the spark is always controlled by the EST siignal, regardless of whether A-B is jumpered or not. So the PCM must send the crank signal directly to the EST output when the jumper is in place, and controls it when the jumper is out. So the timing must be thrown way off when the jumper is out. The only thing that I can think of that would cause that is the cam signal must be way off.
BTW, if the Bypass line is disconnected, the engine really does run directly off the pickup coil, and the ICM shorts the EST line to ground. It actually runs quite smoothly this way, but at a fixed advance. The Bypass line must be a kind of limp home thing in case the PCM spark control completely fails. The Bypass line must be at 5 volts in order for the ICM to use the EST signal.
Also, I figured out why it is throwing the belt. Compared to a picture from Pennock's, the tensioner is in the wrong place. I'd have to make a new home-made bracket to fix it, and get a new belt, because the existing one would then be too long.
Today I found that the Bypass signal is always high, which means that the spark is always controlled by the EST siignal, regardless of whether A-B is jumpered or not. So the PCM must send the crank signal directly to the EST output when the jumper is in place, and controls it when the jumper is out. So the timing must be thrown way off when the jumper is out. The only thing that I can think of that would cause that is the cam signal must be way off.
BTW, if the Bypass line is disconnected, the engine really does run directly off the pickup coil, and the ICM shorts the EST line to ground. It actually runs quite smoothly this way, but at a fixed advance. The Bypass line must be a kind of limp home thing in case the PCM spark control completely fails. The Bypass line must be at 5 volts in order for the ICM to use the EST signal.
A few things to possibly check: EST line is open or grounded PROM or CALPACK not seated properly in the ECM Poor connections between ignition module and ECM Poor routing of EST harness that would give induced electrical noise
He has ordered a dual trace oscilloscope so he can compare things. Also, he had told me that if things were shorted or open, they would be shorted or open both with and without the jumper. Raydar has provided some info he found in the service manual that I passed on to Troubleshooter. With Raydar's vast knowledge of 4.9's, he said it caught him by surprise.
A new bracket was fabricated for the idler pulley. A new and shorter belt was installed due to the repositioning of the pulley. Now, regardless of what the engine does, the belt stays on the pulleys, with or without a jumper in place.
Another tech discovered the distributor was turned one full cylinder and the engine now runs equally well with or without the jumper. Apparently, it's necessary that the distributor be matched up perfectly to the cam. In the next few days, the distributor will probably be pulled and moved at least 1 tooth. At the present time, the distributor is turned to the limit the wires will allow, so the distributor would need to be reset.
Originally posted by fierofool: ... Another tech discovered the distributor was turned one full cylinder and the engine now runs equally well with or without the jumper. Apparently, it's necessary that the distributor be matched up perfectly to the cam...
Well, cool! Is that it? Anything else?
[This message has been edited by Raydar (edited 10-03-2021).]
I'm certainly not quite the expert, but what this post is most recently saying is that the cam sensor signal provided by the distributor hall effect sensor to the ignition module is not in sync with the spark. I believe that the EST signal provided by the module to the ECM also controls the fuel injection cycle. If that signal is a tiny bit out of sync with the distributor firing position I can certainly understand that would cause a problem. While the hall effect trigger position and the distributor position are in a close relationship (made on the same shaft) this may indicate that the timing (distributor) position on the 4.9L is very critical. The problem sounds like it may be very well may be on the way to being solved.
------------------ " THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite. "THE COLUSSUS" 87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H " ON THE LOOSE WITHOUT THE JUICE "
The resolution would be to move each wire one terminal either clockwise or counterclockwise or to remove the distributor and move it one or two teeth. As Scott has stated repeatedly, and it has been verified by others, the timing mark and piston TDC have been verified, so there isn't a problem with the timing chain or balancer.
As Dennis points out, it must be very critical as to how the distributor and cam gear teeth are mated. Someone else had mentioned that possibility, previously.
Raydar had provided a slightly modified chip and initially, it didn't seem to make a difference. After the reorientation of the distributor, Troubleshooter says it does seem to run better with that chip than with the stock chip so it will stay for the time being.
The resolution would be to move each wire one terminal either clockwise or counterclockwise or to remove the distributor and move it one or two teeth. As Scott has stated repeatedly, and it has been verified by others, the timing mark and piston TDC have been verified, so there isn't a problem with the timing chain or balancer.
As Dennis points out, it must be very critical as to how the distributor and cam gear teeth are mated. Someone else had mentioned that possibility, previously.
Raydar had provided a slightly modified chip and initially, it didn't seem to make a difference. After the reorientation of the distributor, Troubleshooter says it does seem to run better with that chip than with the stock chip so it will stay for the time being.
I would move the distributor to correct the timing not the wires. If the distributor is in fact one tooth off the cam gear it may not correct the critical positioning of the hall effect sensor relative to cam position.
------------------ " THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite. "THE COLUSSUS" 87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H " ON THE LOOSE WITHOUT THE JUICE "
Pulling the distributor is the plan. The teeth are large enough that he thinks 1 tooth will do it.
I asked about setting the timing with a scanner afterward and he isn't sure the scanner is the way to go. Raydars method of setting by ear would probably work best.
When I set mine by ear, it was only because setting it with the jumper and light, resulted in not enough power to pull a fat guy from a donut shop. Of course there is always the possibility that my distributor is off by a tooth, too. I had to remove it to do the Allante stuff. But all my wires are on the correct posts on the cap, so I dunno. Maybe my timing ring did slip. With that said... if Scott's is set "by ear", and running correctly, it would be interesting to see what it reads, when checked with the light.
I wouldn't set it with the scanner. I'm pretty sure that all the scanner will tell you is what the ECM thinks the timing is, based upon the premise that the base timing is set correctly, by the book.
Pulling the distributor is the plan. The teeth are large enough that he thinks 1 tooth will do it.
I asked about setting the timing with a scanner afterward and he isn't sure the scanner is the way to go. Raydars method of setting by ear would probably work best.
Pulling the distributor and setting it in the correct position is the way to go. As you may know the 4.9L distributor has both a pickup coil, a reluctor and a separate hall effect switch/sensor that is triggered by a flat on the timer core. If the distributor is moved a notch off of the cam gear the cam sensor function triggers at the wrong point sending the ECM the wrong signals. In other words the distributor position on the cam gear is very critical. Setting the distributor in the right position can very well be the solution.
------------------ " THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite. "THE COLUSSUS" 87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H " ON THE LOOSE WITHOUT THE JUICE "
The car was successfully driven with the distributor twisted. He said he plans to pull the distributor and move it a tooth or two to get the distributor back into the proper position.
Pulling the distributor and setting it in the correct position is the way to go. As you may know the 4.9L distributor has both a pickup coil, a reluctor and a separate hall effect switch/sensor that is triggered by a flat on the timer core. If the distributor is moved a notch off of the cam gear the cam sensor function triggers at the wrong point sending the ECM the wrong signals. In other words the distributor position on the cam gear is very critical. Setting the distributor in the right position can very well be the solution.
So with the wrong Hall effect sensor position, perhaps it's the injection timing that's thrown off, which could cause driveability problems even if the ignition timing is correct, as verified with a strobe lamp.
From tuning my own Fiero (a Fiero V6, but still port-injected like the 4.9), a 90° (crankshaft degrees) change in injection timing could be enough to make the difference between smooth/rough running.
[This message has been edited by pmbrunelle (edited 10-04-2021).]
I managed to "tune" it so that it works better on the original PCM. The curious thing is, when the jumper is in, tuning goes perfectly "by the book". But when the jumper is out, the timing is way off, and it can only be tuned "by ear". I still don't know why that is.
I went on a longer test drive, and the SES light came on during the drive. My scanner said "24 -- cannot determine vehicle speed". I cleared it, but I figure it will come back on the next drive. Maybe Raydar knows how to hook up the VSS.
I think there's a slight miss -- not sure. I got some Sea Foam and put some (not all) in the tank. I'll see if it makes a difference on the next drive. That will be tomorrow, because work and school traffic is out now.
(Note: The VSS harness isn't plugged in. It isn't long enough to reach the VSS.)
Originally posted by fierofool: I managed to "tune" it so that it works better on the original PCM. The curious thing is, when the jumper is in, tuning goes perfectly "by the book". But when the jumper is out, the timing is way off, and it can only be tuned "by ear". I still don't know why that is.
With the jumper in, the goal is not to set the ignition timing that will actually be used to run the engine. The objective is simply to set the distributor to some predetermined angle (assumed by the ECU) relative to the crankshaft. With the jumper is removed, the objective is that the actual spark advance be equal to the spark advance that is commanded by the ECU.
At idle, the engine may run best with 25° of ignition advance (so the ECU is likely to command this much advance), so when the using the strobe lamp, the timing mark may appear off the scale.
The commanded spark advance may vary with RPM, vacuum, among other things.
