Something isn't right w/ my engine

[Schmieder]

Many of you know me to this forum, the 96 GP turbo build.

I have a strange issue with the engine and it is really hard to figure out.

First, the symptoms I noticed today after a long drive.

The ECT read 240 when I decided to shut it off. It became hard to start later and ran a little rough. DTC was a cylinder misfire present. No other DTC's except a lean condition but that popped up after the misfire. That I understand how it happened. Absolutely no knock during that as I was scanning.

When it starts it runs chuggish for a few moments then evens out and idles just fine. I can not find any coolant loss and the exhaust isn't smoking badly. But I can feel an occasional misfire when driving it, not a bad spark plug cable kind of misfire, just an annoying faint misfire only under load. Again, this is only when it is warmed up, and not an OL/CL issue otherwise it would start sooner. It happens after a good drive kind of warm up. And the plenum is hot, not too hot where I can't touch it, but hot. Not sure if that would matter.

Coolant levels are the same, no bubbling. Oil levels are good and stable.

Here is a list of new items to rule out.

Spark plugs, cables, coils. Radiator, pump, hoses, ECT Sensor, thermostat. Heads (complete), gaskets, o2b1, injectors, battery, cam/crank sensors. Oil, filter, flush.

Maybe I am just over reacting and the car is not tuned so it runs hotter then normal. But what is causing the stumbling at start up after a good drive?

Coud this be a failing ICM?

Man, I am perplexed and disappointed deaply. After all that hard work/money and I have this issue to deal with.

edit: btw, I paid extra special attention to the gaskets install. Everything went as it should. All bolts torqued just right in the right order. Thought I'de throw that in the mix.

edit II: Went out and she started right up. Though, the exhaust is smoking a little. But with the weather, it could easily be condensation in the exhaust lines. I know cars can smoke some at start in colder weather like what were having here. And now it idles great. But I bet if I drove it around for a while it would do the same crap it did earlier. We shall see, I'm going to drive it around a bit. I'll report back.

edit III: yup, same crap. When warm the exhaust is clear. But I can not figure this stumbling at start up when it has been driven around. ECT is ok now, it was an idle situation as the idle was high and now I have it set to 800. I guess even in cold weather an idle of 1200 can heat up coolant fast. Plus, the fans were set at a temp way to high, 250. Is that a standard Lumina setting? I put them at start 220, end 200. Fan II is 20 deg higher.

Could a bad fuel pump do this? The pump is 108k miles.

[Weatheralls Auto]

First suggestion I would make is, not making new threads constantly,
Very smart people here, but they will not want to look back your posting history to see what you have done.

Just an observation.

[DefEddie]

You mention codes,but don't post the codes.
Was it a p0300 random misfire or a specific cylinder?
What was the lean code? P0171?
Your tuning,so I kow your scanning-what's going on with trims and inj pulswidths?
More info,less storyline.
And never rule out new parts,ever.
They are less likely to be the cause,but don't rule them out.
I get bad new parts all the time from the dealer,AZ,Oreillys etc..

[Azrael]

The lean reading after the misfire means you might have seen a rich misfire. After a misfire, the unburned oxygen and fuel get dumped into the exhaust and the O2 sensor senses the oxygen (but not the fuel) and gives a lean reading. It happens from either faulty ignition or you're running so rich the mixture won't burn at all.

[Schmieder]

First suggestion I would make is, not making new threads constantly,
Very smart people here, but they will not want to look back your posting history to see what you have done.

Just an observation.

Sorry bout that. I actually try to keep the topic in the specified region.

Hey guys, I figured it out. Cylinder 5's spark plug was shorting out into the exhaust manifold. I saw it and said, "bingo"!

After addressing that issue, it runs real nice again. I guess the engine under load would arc out easier then idle.

Sorry for any vagueness on my part. The DTC was p0300. But the situation is resolved. I'm sitting in my car now after a good drive. Idles nice and keeps a steady op temp of 180. AFR is stable at 14.5-14.3

I kind of freaked and started to post w/o thinking of details. After all the time and money I put into this project, my nerves are on edge.

I'll have a wot vid soon. Got some more tuning to do first

Thank you all for being patient with me and tolerating my quixotic nature.

[Schmieder]

Ok, it is doing it again. Fixing the shorting spark plug boot gave me the impression all was well. So it improved generally but still has a warm start issue. It is a very strange thing. I will try to sum it up plus all the mods done.

When cold, it starts great and runs great. It will not act up during the first run. Even if I drove it for over an hour, as that is the case so far.

Now, when I shut it down it still starts fine. But when I let it sit for 5 minutes it has a little bit of a hard start. If I let it sit for 10 minutes it is even harder. 30 minutes it wants to stall out but won't. After several minutes of running rough it will idle up high into low 2k ranges and level out and then drive fine.

It is the strangest thing!

The error codes I get are p0300 misfire and p0171 lean condition. I know the p0171 is from the misfire and the misfire is from ???. That is what I need to fix.

Now, when the car was started after a 5 minute sit when warmed up, it stumbled slightly AND the AFR was 15.5-16.0. So there is a clue, it may be a dying fuel pump.

Here are some other conditions during the stumbling/rough running.

Intake Air Temps - 75*
MAP - swings around 0-25 kPa
MAF ok, still stumbles in SD mode
No knock
oil pressure is 42 psi cold, 33psi warm
coolant temps no higher then 190*
Alternator is good since 2 days ago when Advanced auto checked it for me (did it for no reason other then it was free info along w/ batt integrity check)

I ruled out coolant leaks. Coolant levels are rock steady and the exhaust is 100% clean when warm. zero bubbles in rad cap and I can't detect any anti-freeze smells (normally any coolant leak I can smell, even head gasket leaks).

Oil is clean, no signs of contamination and has a great psi. Steady level of oil.

No vac leaks. I checked with brake cleaner around the plenum and inspected EVERY vacuum line. The idle didn't flinch a bit.

No changes in MAF to Speed Density modes concerning the issue.

I added a small bit of seafoam through the brake booster line to induce a little smoke in the exhaust. There were no exhaust leaks I could detect and there was a good puff of smoke from the tail pipe.

All spark plug wires are good as they were checked before installation. And the reason the one plug boot was shorting is the wire was pulled back a bit and I needed to cut some of the boots tip off so it can seat the plug. An edge of the wire was arcing into the exhaust manifold. I wrapped it with electrical tape until I can replace them with better quality wires.

The coil packs are about 2-3k miles new as are the spark plugs and cables.

New o2 sensor and the car is great at keeping 14.5-14.3 AFR (set stoich to 14.3)

No real catalytic to be clogged. Test cat.

The fuel pump has a sound like gravel when I turn the key to run, if that makes sense. But no bad sounds after that during operation. Mainly because I wouldn't be able to hear it over the beastly idle the car has. So I am putting a possibility of dying fuel pump on the list. Though, I tried commanding fuel pump High and no changes. Not sure if that means anything.



So, sorry for the very long post. I tried to be as detailed as possible so if anyone wants to lend a hand in figuring this out.

My guesses so far are fuel pump or ICM.

But I don't want to go buying parts until I am a little more sure. My repair budget is very low until next payday. And even then, my wife and I need to replenish our savings. She spent a lot on home furnishings for the move we just had. And the move cost money too. I get heart burn thinking how much we spent combined....lol. I think I had spent near $4,500 for the turbo and other items for the car plus some special tools like a welder, jack stands, ect.

Man this is a loooong post, lol

Anyways, thanks guys for all the help these past weeks.

[AleroB888]

Ok, it is doing it again. ........
The error codes I get are p0300 misfire and p0171 lean condition. I know the p0171 is from the misfire and the misfire is from ???. That is what I need to fix.

Now, when the car was started after a 5 minute sit when warmed up, it stumbled slightly AND the AFR was 15.5-16.0.
....................

When it has the misfiring condition, what are you reading for LTFT's, at idle?

[Schmieder]

When it has the misfiring condition, what are you reading for LTFT's, at idle?

I can't answer that accurately until tomorrow if the hard start happens again. I will data log and get those numbers for you then.

Yhough, iirc, they were always around +20'ish. Even with 36# inj set at 32.44. I should be rich but it wants to add fuel. Maybe that is a sign of a bad fuel pump. The fuel filter was changed out 500 some miles ago. And the inj are refurbished and practically new. Possible FPR going bad? But there is no fuel smell in the vac line and I tried the clear vac line to see if there is fuel droplets, none.

All my LTFT's have been in the positive. Around +17~22 LTFT average cell.

But now they are around -2 ~ +4. I did a 1 hour log and adjusted my VE table accordingly.

One thing to note. Before the logging I was driving with MAF. And during the MAF driving it was easier to want to go lean with too much pedal. With out changing anything but going to Speed Density, it would handle more throttle easier. So it may be possible the MAF sensor is going bad.

Now my LTFT are dialed in. I will do another tuning round tomorrow just to be sure and also try to hit some cells I didn't get. It wasn't easy getting the upper rpm ranges as the trans would always shift on me.

Aside from solving the mysterious hard warm start issue, what is the best way to log higher rpm's? Can I change the shifting speeds/rpm to achieve upper rpm logs? Or is there a better way?

Back to the hard start when warm issue. I think it is possible the MAF is heating up and causing a really bad airflow reading, but that should cause an overly rich condition iirc. Once enough air has passed by it to cool it down, then the readings return to normal. This may be why it never occurs until after a shutdown and heat soaking. Also may explain why it stops after a few moments of rough idle when the PCM catches up with itself during the stumbling misfires. Since it causes a lean reading the PCM pushes more fuel when it is not needed, making the issue worse.

Tomorrow I will try the Speed Density test and see if the hard start is any better w/o the MAF.

BTW, she spools up nicely. At 3500-4000 rpm I'm getting up to 5psi and it sounds beautiful. I love the rushing air sound, makes it feel so bad ass.

I am leaning away from a bad fuel pump, but not ruling it out. It just doesn't seem like the problem. Even though I will get a Walbro 255 high flow soon. I need to test the MAF better to see if that is really it. Or a combination of things like a bad MAF with a dying ICM or weak fuel pump.

It's just one of those issues that is darn hard to pin point. Know what I'm saying? lol. Ughh, engine issues. At least it runs, drives and spools up good.

[Weatheralls Auto]

....... I know the p0171 is from the misfire and the misfire is from ???. That is what I need to fix.......

Not necessarily, You could be getting the misfire from the lean condition.

Sounds to me you are running way to lean, weak fuel pump or messed up tune very likely.

Unless O2 is off and your actually running rich, that would cause the misfires.

[DefEddie]

You need to check for pressure drop on the fuel charge.
A restricted filter can do this,as well as a faulty fuel pump check valve.
When it's hot you need to put a fuel pressure guage on it,cycle the key to get your pressure built up then leave it for a few minutes and see how far it drops.
A few PSI will drop due to vaporization but shouldn't be more than a few PSI.
And put the correct fuel injector flow rating in the computer.

[IsaacHayes]

What are those 36# injectors from? What pressure do they run in the normal application? You have stock 43.5psi pre 2000 regulator right? Just checking to make sure the injectors are what they are at your pressure.

I'd fix that spark plug wire before you go chasing anything else. Just cause you can't see it arcing now, doesn't mean it isn't...

And it might not hurt to swap your old coil packs on.. sometimes new parts are junk or not good quality. Hell I'm running my stock 94 coils that are approaching 250,000 miles....

The CPS (7x) can also get hot and cause issues. Don't get any autozone electronics, they crap out really really really fast. I had the stock CPS crap out, then got an autozone one, and it crapped out a few months later. I thought it was the ICM, turns out it was the CPS again... No wonder it only cost $11 at autozone and the one at O'Reillys cost $28... lol

[Weatheralls Auto]

I would also post a log when you are getting the DTC and issues.

[DefEddie]

Like Isaac mentioned,get the correct fuel flow rating for your size injector's versus pressure.
And you don't get a P0171 from a misfire generally.
Your long trims are +20,and you have a lean code= your running lean.
You either have too much air or not enough fuel.
You don't have an aftermarket MAF (granatelli etc..) do you? And you haven't jimmy'd with the MAF frequency tables?
You need information,fuel pressure checks,leak checks etc..
Lean is generally easy to find,but you have an unknown dynamic (tuning).
You could be lean due to cam etc..
How are you reading AFR? With a wideband?
Your sensor is located BEFORE the cat right?

Just throwing stuff out,I don't know enough about the setup or what's been done.

[IsaacHayes]

Maybe having the MAF right at the front of the TB is not a good idea after all?

[Weatheralls Auto]

LMAO, I forgot about that