Background: you may recall that the success of my '88 2.8L, 2-year long rebuild (including port&polish heads, port exhaust logs, port intakes, 1.6 rockers, Fiero Store valves, and Rodney Power Pulley, cleaned/tested fuel injectors, etc.) was sullied by briefly connecting the ground wires near the starter to HOT which melted a few wires in my harness. After repairing the harness the car started but ran poorly due to water in the gas. After flushing and 2 tanks of fresh gas with IsoHeet the car runs well except for two lingering issues which I have been loath to address:

1) Dash Temp Gauge slowly goes off scale during warm-up.
2) Engine idles well but SEEMS to have a slight misfire and no power.

THIS POST is only asking for ideas on #2, the Idle/Power problem. I started another thread for problem #1 because I feel that they are not related.

Data

a) When I first started the car it barely ran with significant misfires and buckets of water coming out of the exhaust. As noted this declined in severity to where the idle seems normal to me, but in doing a slow throttle increase I detect a slight, regular-periodic misfire (i.e. not random). I've driven the car several hundred miles now but it stopped improving.

b) I did a propane 'leak test' all around the hoses and fittings and detected no idle increase so I think there are no vacuum leaks.

c) Before the rebuild/upgrade the acceleration was at the so-so level that seemed consistent with my prior Fieros but now it seems even less peppy, never giving that 'pull' feeling it used to show a bit in 2nd or 3rd gear.


I'm at a loss of where to start diagnosing this or even validating that something 'is wrong.' I'm not 100% sure there is actually a misfire. One other thing, I've kept my registration current but I really shouldn't drive it with expired plates. A smog test is needed and I'm worried to go get one and find I now have a 'gross polluter' on my hands.

Is your ignition timing good?

If the harmonic balancer slipped, then you would be timing the engine using incorrect reference marks, resulting in incorrect timing.

Did you use a refurbished harmonic balancer on the rebuild?

quote Originally posted by pmbrunelle: Is your ignition timing good? If the harmonic balancer slipped, then you would be timing the engine using incorrect reference marks, resulting in incorrect timing. Did you use a refurbished harmonic balancer on the rebuild?

Hmmmn, well I was able to set the timing using the cylinders 1 (and 4?, whatever the right one is). But I did reuse my old balancer with the old marks.

And did the rubber look good or deteriorated?

If the rubber had deteriorated, then the exterior ring of the balancer could have slipped.

What if, without the paperclip-in-the-ALDL, you simply rotate the distributor to find the strongest idle?

[This message has been edited by pmbrunelle (edited 07-11-2020).]

Well, it certainly didn't look like a newer balancer but I'll check it more closely this week and try the distributor experiment you suggested.

Additional Data:

1) I warmed up the car in pretty much pitch dark conditions and looked at the ignition wires and boots. No evidence of arcing to ground. This seems like a good result however I have never had occasion to see arcing in the past so I don't even know if it is visible.

2) I then tried the experiment of rotating the distributor while NOT putting in the clip. The position adopted from my prior timing job ran the best. Advanced a bit and it started to misfire at idle (normally I only hear the misfire at higher revs) and retarded a bit, same story. I don't really understand what this did except prove the correctly set timing ran the best at idle.

Any thoughts?

Have you checked each spark plug wire for resistance to see if they are all within spec?

quote Originally posted by Patrick: Have you checked each spark plug wire for resistance to see if they are all within spec?

Ah hah! So in doing this just now I found that 5 of the 6 wires were in the range of 7.6 - 8.5 kohms. For the 6th wire the plug boot came off but the clip remained on the plug and the conductor was left flapping in the breeze. I'm tempted to declare victory, unless I have merely destroyed a wire that was otherwise OK. In any event, I just ordered the Fiero Store wire set and will see what-is-what after they arrive. In the meantime I can go to sleep now nursing the hope that 'this was the problem.'

[This message has been edited by Notorio (edited 07-21-2020).]

Don't take any short cuts. Now that you have the wires disconnected from the spark plugs, remove all the plugs and check to see if one (or more) look different than the rest. Should all be the same color. Also re-check the gaps.

quote Originally posted by Notorio: I don't really understand what this did except prove the correctly set timing ran the best at idle.

That was the point of the test, to confirm that the timing was set correctly... to exclude the possibility of incorrectly set timing.

The spark plugs themselves also have a resistor between the post and the centre electrode, so you can check those too.

[This message has been edited by pmbrunelle (edited 07-22-2020).]

I made the mistake of installing Taylor spark plug wires during an engine rebuild. After months of ruff idling and lack of power I noticed burn marks on my red plug wires. I found almost all had black spots where they touched each other and some where they touched metal. Make sure all wires are isolated or have wire sleeves over them where in close contact.
Wow what a difference it made in power after the fix.


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∇PONTIAC∇
“The difference between a Fiero owner
and a genius is that genius has its limits.”

[This message has been edited by Imnuts (edited 07-22-2020).]

Major Update today ... I've been too busy to do anything with the car so I brought it to a speed shop that also does Smog, since I'm still driving on expired tags. In a one-hour diagnosis to look for a slight misfire he found:

1) Spark OK to all cylinders
2) Compression OK on all cylinders
3) Leak-down test failed on #6 at 35% vs normal of 5% or so.
4) All spark plugs appeared normal except #6 which was fouled with oil
5) Vacuum gauge fluctuations point to incomplete combustion.

Something I forgot to mention to him (and you guys) is that the oil gauge pressure has been running LOWER than before I did anything to the engine, including the high-volume pump. Something else to keep in mind is that #6 has two heli-coils but torqued down just fine.

So WHERE is the oil coming from that is doing the fouling? He suggested:

A) Bottom End. Since I related the story of the terrible misfiring and shaking on first start up due to water in the gas tank, he thought there was a possibility that there might have been an initial hydrolock-like situation which could have bent a rod enough to create the failing leak-down test. So in this case the oil would be coming up from the bottom past the rings, now somewhat tweeked by the bent rod.

B) Top End. Bad valve stem oil seal, damaged valve seat or valve guide. Bent pushrods from using 'stock' rods with the 1.6 roller-tip rockers. He didn't believe me that 'lots of people on the forum have done this upgrade and just use New, standard pushrods'. He said I should have checked for clearance myself ... my bad .

So now I have to tear down part of the engine again. I thought I would just bring the Even head to the shop and let him do the measurements, etc. One thing he said I should do is to measure the piston height at TDC on #6, 4, and 2, which would show if the rod has bent. The motor runs too well otherwise so he didn't think I cracked the block (yet.)

To be honest I am very loathe to tear that down and make the car undriveable again after 2 1/2 years of working around the hulk in the garage. At least as it is right now I can move it under its own power. Are there any recommendations out there? Alternative theories??

[This message has been edited by Notorio (edited 08-06-2020).]

quote Originally posted by Notorio: B) Top End. Bad valve stem oil seal, damaged valve seat or valve guide. Bent pushrods from using 'stock' rods with the 1.6 roller-tip rockers. He didn't believe me that 'lots of people on the forum have done this upgrade and just use New, standard pushrods'. He said I should have checked for clearance myself ... my bad .

What "clearance" is he referring to? Valve to piston clearance? Are your pistons stock?

I used new "stock" pushrods when I upgraded to 1.6 roller tip rockers with no issues (original cam). Unless you totally botched up finding zero lash and/or adjusted way too much preload on the lifters, I don't see how "clearance" should've been a problem.

Any chance you damaged an intake valve guide seal during installation?

quote Originally posted by Patrick: What "clearance" is he referring to? Valve to piston clearance? Are your pistons stock? I used new "stock" pushrods when I upgraded to 1.6 roller tip rockers with no issues (original cam). Unless you totally botched up finding zero lash and/or adjusted way too much preload on the lifters, I don't see how "clearance" should've been a problem. Any chance you damaged an intake valve guide seal during installation?

Yes, valve to piston. The pistons are stock (I didn't do anything to the short block other than the new oil pump and timing chain) and I just assumed that the cam was original. It is of course possible that I botched the lash adjustment ... I followed the manual but might have zoned out or gotten distracted perhaps on that valve. Probably it is more likely that I damaged the valve guide seal during installation.

quote Originally posted by Notorio: 3) Leak-down test failed on #6 at 35% vs normal of 5% or so. Something else to keep in mind is that #6 has two heli-coils but torqued down just fine. So WHERE is the oil coming from that is doing the fouling? A) Bottom End. Since I related the story of the terrible misfiring and shaking on first start up due to water in the gas tank, he thought there was a possibility that there might have been an initial hydrolock-like situation which could have bent a rod enough to create the failing leak-down test. So in this case the oil would be coming up from the bottom past the rings, now somewhat tweeked by the bent rod. B) Top End. Bad valve stem oil seal, damaged valve seat or valve guide. Bent pushrods from using 'stock' rods with the 1.6 roller-tip rockers. He didn't believe me that 'lots of people on the forum have done this upgrade and just use New, standard pushrods'. He said I should have checked for clearance myself ... my bad . So now I have to tear down part of the engine again. I thought I would just bring the Even head to the shop and let him do the measurements, etc. One thing he said I should do is to measure the piston height at TDC on #6, 4, and 2, which would show if the rod has bent. The motor runs too well otherwise so he didn't think I cracked the block (yet.) To be honest I am very loathe to tear that down and make the car undriveable again after 2 1/2 years of working around the hulk in the garage. At least as it is right now I can move it under its own power. Are there any recommendations out there? Alternative theories??

Its obvious that something is wrong on cylinder #6. You will need to pull the heads and take a look or use a fiber optic camera to look in through the spark plug hole to inspect the cylinder. If the piston to valve clearance is not there you will see marks on the piston tops but interference problems don't normally show up on just one cylinder.

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" 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 "

Success ... I'm not hearing things: the misfire is real. The head is off and the diagnostic confirmed ... #6 is as dead as a doornail (no carbon deposits). Also, no sign of valve-strike damage to the piston (and bend the rod) and no obvious cracks to the valve seats (to open a leak path). I was thinking I would drop the head off with the expert Monday AM rather than take it apart myself. Pretty much the only thing I could do would be to re-lap the valves and install new seals. What could be causing the 35% leak-down failure? The head gasket looks fine.

p.s. cylinder #s edited in per request

[This message has been edited by Notorio (edited 08-10-2020).]

quote Originally posted by Notorio: I brought it to a speed shop... In a one-hour diagnosis to look for a slight misfire he found: 1) Spark OK to all cylinders 2) Compression OK on all cylinders 3) Leak-down test failed on #6 at 35% vs normal of 5% or so. 4) All spark plugs appeared normal except #6 which was fouled with oil 5) Vacuum gauge fluctuations point to incomplete combustion.

quote Originally posted by Notorio: What could be causing the 35% leak-down failure? The head gasket looks fine.

I'm curious if the shop did the leak-down test first without, and then with oil being squirted into #6 cylinder?

Wet Compression Test

[This message has been edited by Patrick (edited 08-09-2020).]

How can compression be OK.....and fail a leak-down test....which is checking compression?

Notorio, could you number the combustion chambers on the pic? Why does one chamber look like it has never fired once? (is that #6?)

[This message has been edited by Gall757 (edited 08-09-2020).]

Turn the head upside-down and fill the combustion chambers with kerosene. Leave it overnight.

If you have leaking valves on the "bad" combustion chamber, you'll see the kerosene leak out into the ports (comparing the bad vs good cylinders). A lack of compression can also be due to a problem with the bottom end.

You said that your injectors were tested, but that doesn't mean they were all functional as installed in your Fiero.

If you plug the injectors into the car's wiring, and have a friend crank the car over, do you feel all the injectors clicking?

[This message has been edited by pmbrunelle (edited 08-09-2020).]

quote Originally posted by Patrick: I'm curious if the shop did the leak-down test first without, and then with oil being squirted into #6 cylinder? Wet Compression Test

Beats me. I'll ask when I see him tomorrow.

quote Originally posted by Gall757: How can compression be OK.....and fail a leak-down test....which is checking compression? Notorio, could you number the combustion chambers on the pic? Why does one chamber look like it has never fired once? (is that #6?)

I have updated the original picture now with the cylinder numbers. My limited understanding was that the Compression Test gives the max pressure while cranking and that the Leak Down Test tracks how well the pressure holds during a two-minute rest, with 5% loss being typical and 35% being indicative of serious trouble. So all the parts taking place in the 'sealing' process are able to hold the pressure briefly for the Compression Test where cranking continues but fail in 'long-term' sealing after cranking has ceased. (Now why that is relevant escapes me. Ogre?? When I think about it I'd presume that if the pressure held 'ok' on the hundred millisecond timescale you'd be good to go, but I'm too tired right now to calculate it out.)

quote Originally posted by pmbrunelle: Turn the head upside-down and fill the combustion chambers with kerosene. Leave it overnight. If you have leaking valves on the "bad" combustion chamber, you'll see the kerosene leak out into the ports (comparing the bad vs good cylinders). A lack of compression can also be due to a problem with the bottom end. You said that your injectors were tested, but that doesn't mean they were all functional as installed in your Fiero. If you plug the injectors into the car's wiring, and have a friend crank the car over, do you feel all the injectors clicking?

I would LOVE to run that Kerosene experiment except I don't have any.

The injectors were sent to a cleaning and calibrating service that measured the output before and after servicing. I'll have to dig out the paperwork but I recall them being 100% after the cleaning. However, and perhaps this is an ominous point, those were cleaned at the BEGINNING of this 2+ yr adventure so they sat in their little sealed baggies for about 2 years before I put them in and fired the engine up. I'll have to try your experiment tomorrow!

On a side note, I wonder if there are TWO problems here, with Problem 1 causing the leak-down failure but Problem 2 (i.e. #6 faulty injector spraying little-to-no gas into the lower intake runner) causing the 'no-fire' condition that I HEAR as a misfire and FEEL as lack of power, and MEASURE as a vacuum gauge fluctuation, and SEE as a Combustion Chamber that still looks as clean as a baby's behind?? I certainly don't understand how having just Problem 1 would result in Zero Combustion if Gas and Air were actually present.

[This message has been edited by Notorio (edited 08-10-2020).]

quote Originally posted by Notorio: The injectors were sent to a cleaning and calibrating service that measured the output before and after servicing. I'll have to dig out the paperwork but I recall them being 100% after the cleaning. However, and perhaps this is an ominous point, those were cleaned at the BEGINNING of this 2+ yr adventure so they sat in their little sealed baggies for about 2 years before I put them in and fired the engine up.

I think the concern that pmbrunelle has (and one that I was wondering about as well when I looked over your checklist), is how was the operation of the injectors checked when installed? In other words, the injectors themselves could be fine, but perhaps there's an issue with the injector harness etc?

If the #6 plug was working, there would be some slight discoloration of the combustion chamber. Seems like the problem (or one of the problems) is no spark.

Some breaking news ... went to drop off the head at the shop and showed him the combustion chambers and suggested that the #6 fuel injector was responsible for the lack-of-combustion with very limit deposition. Turns out after verifying spark he bore-scoped #6 and could see the injector spraying gas. So unless the fuel injector stops working at idle and greater rpm, looking 'ok' at cranking rpm, then my theory is kaput.

He advised taking the head to a specialty shop an hour's drive from here for really checking for cracks on the head or seats. Not ready to commit to that so I thought I'd round up some kerosene and try that leak-down test (maybe in the cylinders as well) but couldn't find any in the PRC.

quote Originally posted by Patrick: I'm curious if the shop did the leak-down test first without, and then with oil being squirted into #6 cylinder? Wet Compression Test

quote Originally posted by Notorio: Beats me. I'll ask when I see him tomorrow.

What did he say?

quote Originally posted by Patrick: What did he say?

Doh! I was so flustered by his 'the fuel injector works' comment that I forgot to ask.

I suggested kerosene as a "readily-available" (in my mind) liquid.

We need a liquid that is not repelled by oily deposits on the heads, nor anything too volatile that will evaporate on its own. We also don't want too much of a fire hazard.

Some alternatives that come to mind:
Paint thinner
Varsol
Diesel fuel
WD-40

quote Originally posted by pmbrunelle: I suggested kerosene as a "readily-available" (in my mind) liquid. We need a liquid that is not repelled by oily deposits on the heads, nor anything too volatile that will evaporate on its own. We also don't want too much of a fire hazard. Some alternatives that come to mind: Paint thinner Varsol Diesel fuel WD-40

Eureka! I found quart can of Kerosene at ... Walmart ... so I start start running this experiment today.

Two more pieces of data:

1) Result of Kerosene leak-down test on the even cylinder head. Combustion chambers #2, 4, and 6 all look the same, showing what I think was just a small amount of loss due to evaporation. I take this to mean no sign of a bent valve or a serious leak.

2) Result of measuring gap between piston at TDC and a straight edge across the cylinder. Gaps for #2, 4, and 6 all are 0.035" +/- a bit. I take this to mean no sign of a bent rod.

Conclusion

For cylinder #6, I somehow damaged the rings during the very rough start-up that opened a leak path for oil (up onto the spark plug) and for air-gas (down into the oil pan) such that the cylinder doesn't fire, even though Gas, Air, and Spark are present, yielding the 'misfire' that started this investigation.

Seeking your thoughts on this ...

Is this the right conclusion? Are there alternative conclusions? Suggested Next Steps? If I choose to just change the oil and put it back together, would mildly driving the car in this state now and then cause further harm? This would give me time to save $ and also not leave an abandoned hulk in my garage again.

quote Originally posted by Notorio: For cylinder #6, I somehow damaged the rings during the very rough start-up that opened a leak path for oil (up onto the spark plug) and for air-gas (down into the oil pan) such that the cylinder doesn't fire, even though Gas, Air, and Spark are present, yielding the 'misfire' that started this investigation.

What was there about the "very rough start-up" that would have damaged the rings, the piston and/or the cylinder walls on one cylinder of the six?

quote Originally posted by Patrick: What was there about the "very rough start-up" that would have damaged the rings, the piston and/or the cylinder walls on one cylinder of the six?

My theory is that it was the severe water-in-the-gas issue. The engine bucked and coughed and spluttered to life with a very rough idle and misfire. I thought perhaps by chance fuel injector #6 got the lion's share of water vs the other cylinders. The walls of the cylinder look fine. When I took the engine apart initially all 6 cylinders looked about the same in terms of deposits so the rings must have been damaged after that. The only thing I can think of is the water ...

[This message has been edited by Notorio (edited 08-12-2020).]

quote Originally posted by Notorio: My theory is that it was the severe water-in-the-gas issue. I thought perhaps by chance fuel injector #6 got the lion's share of water vs the other cylinders. ... so the rings must have been damaged

I'm definitely no expert, but I'd think if there was that much water that the cylinder would've hydrolocked and stopped the engine from running.

The following article does say that pistons can be damaged, but doesn't actually mention rings.

Hydrolocked Engine – What Is It – What Damage Can It Do

quote Originally posted by Patrick: I'm definitely no expert, but I'd think if there was that much water that the cylinder would've hydrolocked and stopped the engine from running. The following article does say that pistons can be damaged, but doesn't actually mention rings. Hydrolocked Engine – What Is It – What Damage Can It Do

Good reference on hydrolock. I guess I will have to drop the oil pan, ream the ridge, and push the piston out the top to see if the Rings or the Piston are damaged and leaking. Any other theories out there? Recommendations? Today I'll rotate the crank to get #6 and #4 at the same height and run another Kerosene leak-down test. This way I will see if the horrible result on #6 is repeatable and also see if #4 hardly leaks at all, like #2.

quote Originally posted by Notorio: Good reference on hydrolock. I guess I will have to drop the oil pan, ream the ridge, and push the piston out the top to see if the Rings or the Piston are damaged and leaking. Any other theories out there? Recommendations? Today I'll rotate the crank to get #6 and #4 at the same height and run another Kerosene leak-down test. This way I will see if the horrible result on #6 is repeatable and also see if #4 hardly leaks at all, like #2.

The plan makes sense.

Since you don't have many miles on the engine, there probably isn't much of a ridge, so you should be able to push out the piston as-is.

quote Originally posted by pmbrunelle: Since you don't have many miles on the engine, there probably isn't much of a ridge, so you should be able to push out the piston as-is.

The images Here don't appear to show a newly rebuilt engine.

Notorio, what is the history of the bottom end of this engine?

quote Originally posted by Patrick: The images Here don't appear to show a newly rebuilt engine. Notorio, what is the history of the bottom end of this engine?

The bottom, with 98k miles, only got a new high-volume oil pump. I can 'feel' a ridge but am going to try to measure it.

Here is the result from rerunning the Kerosene leak-down test on #6 (bad cylinder) and comparing now to #4 as a second reference for a 'good' cylinder. I promise I didn't put my thumb on the scale ... #6 is dead on it's prior result and #4 performs just like #2 did. So if there are no objections out there I'm taking this as comfirmation that #6 piston has been damaged sufficiently to have a significant leak-down problem. Looks like I'm going to have to take the oil pan off

quote Originally posted by Notorio: So if there are no objections out there I'm taking this as comfirmation that #6 piston has been damaged sufficiently to have a significant leak-down problem. Looks like I'm going to have to take the oil pan off

This is rather beyond my experience level. If it turns out that the piston needs to come out of there, I'm certainly interested in seeing what the actual issue is.

I (incorrectly) assumed that this was a rebuilt engine.

Yeah, I think it's time to take out that piston.

This is what I found in my Fiero 2.8 V6:


The damage wasn't really visible from above; I only knew the extent of what had happened once I removed the piston.

From the driver's perspective, this engine was still running and driving OK.

[This message has been edited by pmbrunelle (edited 08-13-2020).]

quote Originally posted by pmbrunelle: This is what I found in my Fiero 2.8 V6...

Any idea what might've caused that?