Still fighting my skip/miss

**Zapper2003** · 05-19-2009, 07:57 PM

Okay, so i've finally got back in gear to fix this car. Its a 97 Formula, lt1, a4. No engine mods. K&N filter, dynomax catback, thats it. Here's the symptoms. I swear this will never give me the same symptoms twice. Today, after sitting for approximately 8 months untouched, it fired right up. Still missing a little throughout the RPM range, and a bit of hesitation off idle (which is fast, by the way, 1100 or so)and blowin black, unburnt smellin' exhaust out the tailpipes. Already did plugs and wires, had the ICM tested, still hoping its not the opti. When I parked it, it would start and run, idling fast, stumble off idle (sometimes nearly stalling) and run rich and skip/miss. I always thought the miss was just low in the RPM range, but i've come to see that its doing it all the way through the RPM range. I haven't had the coil tested, but I'm leaning towards it being a bad opti. The car sat for 2-3 months last spring in the front yard on grass so i'm guessing it was moisture. Runs this poorly and still doesn't throw a CEL. Any Ideas?

**JoshieDoom** · 05-20-2009, 01:14 AM

Gotta be the opti bro

**JaycenK** · 05-20-2009, 01:11 PM

LT1 cars are slow to report codes. When I dump my computer it will take it several hours to throw a CEL. Mine dose it because I took of the egr off and have not had it taken out of the pcm

**Zapper2003** · 05-20-2009, 01:49 PM

Okay, so maybe that makes a little sense. I haven't driven it for fear of it breaking down and not re-starting, or causing me to stall in an intersection or some such. It's been started maybe a dozen times since this first occurred, however, the battery has been dead or removed a few times since.

**JaycenK** · 05-21-2009, 10:08 PM

Yea everytime you take that battery off or it dies the codes are dumped. I have no idea if a scanner will help or not because there are no codes to check. Acouple of odds and ends you can look at before changing the OPTI are the TPS, MAPS, and the mass air. When a TPS goes bad it will give you alot of problems with idel. one of the most common is stalling. If you have a chiltons manual and a multimeter you can diagnos them fairly easy. Testing instructions are in the Chiltons. Not sure about the haynes.

**Zapper2003** · 05-22-2009, 03:13 AM

It has an audible skip/miss and smells rich out the tailpipes which leads me to think its spark or fuel related. Would the tps still do that?

**t-rock** · 05-22-2009, 03:15 AM

my 94 is missing throughout the rpm rannge too but idles fine. if you get on it sometimes it will die sometimes it wont i just dont get it, i have replaced the opti with in the last 6 months plugs wires coil and icm. im about ready to start throwing rocks at it!

**Zapper2003** · 05-22-2009, 03:19 AM

Thats how mine is. It idles okay, but fast (1100 or so), but once you hit the gas it stumbles down to 600 or so then takes off, revs up while missing the whole time and then returns to its fast idle just fine. Even in gear it idles fast, around 8-900rpms.

**JaycenK** · 05-22-2009, 06:59 AM

Did you guys check your fuel pressure?

**Zapper2003** · 05-22-2009, 11:47 AM

I have not.

**t-rock** · 05-23-2009, 03:05 AM

yes but mine does not stumble on take off. it revs up fine in park or when put your foot on the brake put it in gear and give it gas. its dead miss when driving. i wonder if the intake is leaking im gonna check that today.

**JaycenK** · 05-23-2009, 09:03 AM

yea could be there was a big problem with the intake leaking back by the cowl I belive. If you haven't checked fuel pressure just turn the key to run but don't start the car so you can cycle the fuel pump. do that 3 times and then get out and use a small screew driver to realese the valve on the fuel rail. If fluid spits out your probably good. if it just trickles out or you get nothing it can be 2 things. 1. the fuel pump is not working(mechanical or electrical) or is weak. or the fuel pressure regulator may be bad. I don't think the fuel pump pumps at different rates like the old days, it just supplies pressure and the regulator controls line pressure based on vac. you could try pulling the vac line off the pressure regulator and that should supply max line pressure if I remember right and see if it helps either of you.

Zapper you may have a bad OPTI so nothing should change if you have fuel pressure.

T-rock one other thing that you can check before the intake it the MAPS sensor on top of the intake. you can test the sensor with a vac tester kit from a local parts store and a multimeter. Test details are in the chiltons as to what values you should have. The sensor has a stupid rubber gromet arround it that can leak but I have had my 97 since new and GM had to replace the intake gasket on mine but when they did they took that sensor off and when they put it back in they din't fit it in the hole right so after time the rubber shrank and I ended up with a leak that caused me a load of problems when I put a preformance auto trans in. Not really sure that this would cause your problems but it only takes a minute to check these, and theMAPS does provide data to control timming.

**Zapper2003** · 05-24-2009, 04:12 AM

Alright, so what you're sayin' is just pull the vac. line off the regulator and try running it once? Do i pull that off AFTER the engine is started or before? I won't blow anything will I?

**JaycenK** · 05-24-2009, 06:14 AM

no Just put a plug on the vac line. if you have already checked fuel pressure and then you should have checked it with the vac line off.

**t-rock** · 05-24-2009, 09:17 AM

i put the new icm on it this morn and it ran fine for 15 miles no miss everything was great.
then i let it sit for about an hour and half start it up put it in drive and as soon as i touched the gas pedal it dies and will half to wait for a while to restart. fuel pressure is fine my mind is not.

**JaycenK** · 05-24-2009, 09:51 PM

Man I hate that for ya. Your prob sounds like it is electrical. Heat seems to be the trigger. If you have replaced the opti ICM PLUGS wires all that I would say it is time for a multimeter to test all the sensors and PCM input devices like the TPS MAF MAPS TEMP and some wire inspection. Check to make sure the altenator output post isn't grounding out on anything.
Do you have headers?

Have you changed the fuel filter?
If not or if you have the old one I would cut it open and check it for crap.
Make sure the positive battery cable hasn't worn off it's jacket on something running down to the starter. Other than that I am kind of out of ideas if all that is good. Might want to post this on LS1Tech and see if anyone can come up with something.
The sad thing is it is almost always something so simple and so stupid when you figure it out you will be like OMG you have to be joking. Sry man
Do you have any codes?

**t-rock** · 05-25-2009, 03:31 AM

no headers fuel filter has 4 thousand miles on it and no codes.
its definately something that gets heat soaked.
when it wont start i can take the coil wire off the coil and its not firing.

**Zapper2003** · 05-25-2009, 05:04 PM

Here's a link someone found for me a while ago. I just went through and re-read the entire thing again. I STILL have no idea what the hell the problem is.

http://www.camaroz28.com/forums/arch...p/t-61111.html

**JaycenK** · 05-26-2009, 09:18 PM

This is an old trick I had to learn from some mopar guys back in my teen years, but might be worth a shot. First off make sure all of the ground conections to the car are clean of rust, paint dirt, ect. There are several in the engine bay.
With a fully charged battery, disconect the one wire feed from the altenator. The thicker wire with the boot.
TAPE THIS WIRE UP REAL GOOD WITH ELECTRICAL TAPE!!!! Secure it so it will not touch anything and put the nut somewere you will not loose it. Now run your car and see if it changes any of your problems. Don't run it for to long because it will drain the battery fairly quickly on this modern electrical nightmare.
A bad regulator in the altinator can cause a miss.
Also chack all of your battery cables. trace them all the way to end to see if any of them might have cuts or may have rubbed the jacket off and may be shorting out. LT1 cars have the POS from the battery run low through the engine bay and a piece of road garbage can hit them. They also are run into wire loom down low and if the car ever had a battery go bad (all side post batteries do this) and leak acid down the cable, the acid can get into the loom and destroy the loom and creat a place for the cable to rub. I have this problem on my 97 caused from acid.

If you have replaced the parts you said you have then thier should be no reason it dosn't run. It has to be electrical.

**t-rock** · 05-31-2009, 05:11 AM

well for me it was the opti i changed it yesterday.
the cheap chinese made opti from summit i bought back in december of last year for $250.00 turns out it is pure junk.
once i compared it to my original one and the the one i bought yesterday i could tell it was very cheaply made.
there wasnt any type of seal around the pick up coil which let in moisture and after 4000 miles the bearing was toast.
zapper your symtoms remind of the origanal reason as to why i changed my opti back in december.
but it was a plug wire that had burnt in two once i tore into it.
i was only two bolts away from having the opti replaced so i changed it and it led to this problem. my origanal opti lasted 135,000 miles and the chaepo from summit lasted 4000. they did say they would refund my money.