OK, I'm starting a new thread on this problem since I've changed so many things and the problem is slightly different now. Also I am PMing two other members with the same problem (I think).
88 coupe A4, 170 k miles.
The problem:
After at least 20 minutes, at idle in gear it starts missing, sputters on take off, reduced power, keeps running, never dies. If I pull over and rev it to 2500-3000 for 30 seconds it clears up somewhat, sometimes. Run down freeway at 70 mph 10 miles, clears up, runs fine, sometimes.
The next morning, starts and runs perfect for 20 minutes. Shows no codes, Starts quickly, idles at 1100 for a few seconds, comes down to 700, then 600 after a minute, goes up when A/C kicks on.
I have changed:
O2 sensor, cap, rotor, wires, module, terminal block with capacitor, plugs, coolant temp sensor (someone told me the 88 has two, but the parts guys can't find a listing for a second. I see a larger sensor right next to the c/s I changed with a black cap held on with a SS clip- is this it, anybody have a part number please?) I bypassed the throttle body coolant, changed the thermostat to 180 deg. New housing (original cracked upon reassembly).
I bought a TPS but it gave screwy readings, so I put my old one back on and set it to .60 (runs better than at .54)
I took off the throttle body, removed the IAC and TPS and cleaned it with Injector Cleaner (Just the end of the IAC). Spotless now, had lot of carbon build-up. Drilled and tapped broken off TPS screw (Everything is so easy on an old car.)
I have not touched the injectors yet because I did not want to change too many things at once in case I had a different problem I could go back to where I last was. Good thing too, since it would not run with the new TPS, which I returned and got a refund.
Anybody got a possible cause for this "Christine" like behavior?

 

I should probably go back and read your other post Ed. I did alot of trouble shooting on a intermittent, so I'll just list some things I'd check.

Ohm the injectors
Ohm the pickup coil-you have to wiggle the wires while doing this!
Use a noid light on the injector pigtails (that's where I found mine).
A very patient check for those illusive vac. leaks
I think you may have done this already-fuel pressure test?
By saying you replaced the "modul" do you mean ignition modul? Autozone can test those!

BTW, what did your old plugs look like when you pulled them?

 

Thanks for the reply. Yes I mean the Ignition module was changed, I just can't type. I don't mind spending the money for new injectors since these are 18 years old unless that is a waste of money, what do you think. Summit racing has them for $249 plus $34 for the ninth injector. Ebay has a set of 88 OEM's up for sale, 8 days to go, I may bid on those instead. I will OHM them first. What is a noid light? Pardon my ignorance. I am new to fuel injection problems. I can take a carb apart and rejet/rebuild with no problem, four at a time on my bike. Any thoughts on the location of the second coolant temp sensor? How about the location of the ninth injector. Also what pickup coil, I asume you don't mean the dist. coil. Where is this coil. Oh, the plugs look fine, all even light tan color, maybe a little too white. I haven't done a fuel pressure test yet, the problem doesn't occur until 20 minutes, and goes away. Could this be a fuel pressure problem? I'm thinking sticking injector.Ed

 

First..I think as far as the temp sensor, somone might have been referring to the one on the passenger side..don't worry about it, when guys refer to the CTS causing issues their talking about 1, the one in front by the thermo.

A noid light is a test light that plugs into the injector pigtail.. I got mine from a local speed shop, NAPPA and Autozone didn't have them, I understand Pepboys does. What it does is show the injector pulsing-lets you know the signal is getting to the injector...nice tool to have,
mines a ASTRO PNEUMATIC TOOL COMPANY, came with 6 noid lights and 2 IAC signal testers, very nice set and cheap-here's there number for a dealer near you 1-800-221-9705.

Cmon Ed, you need to ohm that pickup coil too!

I wouldn't worry about the 9th injector (cold start injector) I really doubt it has anything to do with your problem!

As far as replacing your injectors..if they OHM good, and are not the cause of losing pressure...if it were me..no way, but I usually Seafoam my engine at least every other year, seem to keep everything clean, injectors included.

 

When the injector coils started to short out on my 90 it did the same thing. The closer the motor got to normal operating temp the more pronounced the miss, sputter got. They got real bad real quick and it wouldn't even run well at idle eventually, you could hear the miss and the right exhaust smelled lean. I finally had a scan done and I was shown the data & it was explained to me what I was looking at and why the data was telling the injectors were not firing correctly.

You need to ohm test the injector when cold and then when normal operating temp is reached unless they are really bad like mine were.

Good luck, I was told it's the ethanol in the gas here in the Neast, they were not designed to work with ethanol.


Tom

 

Injector coils, pick up coils, are these the same. Where are these?

 

No Ed, their not the same, the pickup coil is located in the distributor,it's actually a round magnetic object with wires (electronic magnet net if you will) If I remember right two wires, which plug into a connection.

The injector coils health is what you're measuring by ohming the injectors.

Ed, hate to say this...but you sound like you haven't got the FSMs or Helms manuals? ANYONE working on a C4 or newer vette has got to have these..they are the cheapest tool you'll ever buy, about $100. without them you're gonna throw away that much in replacing perfectly good parts...the trouble shooting flow charts themselves are worth $100.

 

. The pick up coil in the distrubitor could be the problem as well as injectors or injector wiring. As stated before, test or get the pick up coil tested at say, autozone. The noid light will check refrence pulses from the ecm that the distrubitor sends. You need to get a fuel pressure guage and check pressure key on, at idle cold, tape it to your windhield and go for a drive. Watch pressure in various RPM ranges and at WOT...check pressure engine idle hot. If there is a drop in pressure while driving > fuel pump not keeping up. Ohm the injectors one by one (16+/- 1 ohm) cold and hot. Do all the plugs look the same? This is a lot of work but were don't have our hands on the vette, so just suggestions.

 

can't have autozone check the pickup coil, and if it needed replacement
you'd have to pull and disassemle the dist.

 

Well I don't have the FSM, and I'm not sure I could follow it if I did, I'm not a tech. The car runs fine except it loads up when idling in gear I have found, reving it clears it out everytime now that I've replaced and cleaned everything from the dist to plugs, and cleaned and adjusted the throttle body. If it wasn't getting fuel, it would not clear out by reving it. It runs too good to be lack of fuel.Same goes for the pick up coil, higher revs would only put a higher load on it. I think it is getting too much fuel while idling because of the cold start valve not shutting off. I have tried to locate a cold start valve and thermal switch, no luck so far, the parts are discontinued. I have a guy looking for the parts for me who is very knowledgeable. I wonder if shutting off the fuel to this valve is possible, but I'm not sure which one it is. Any help locating it, and the thermal switch would be appreciated. Photos would be even better. Thanks for your help, Ed

 

ED, the CSV is located on the drivers side fuel rail more towards the back middle. It is the "9th" injector and is only use for cold starts. You can look at the rear right side of the intake and curved metal line that goes around to the injector. The thermal time switch is located on the front of the intake manifold and will send power to the CSV circuit beyond it. It will only work with cold temp <100* outside and it only sends a signal for 8 seconds before cutting off. There is also a fuse for the CSV located behind the DIC. There are about 3 or 4 hidden fuses there, it's a 5 amp. Now there is no way of knowing if the CSV is leaking unless you take it out and with the engine hot see if it sprays or leaks.

 

I think I should name my Vette Christine because it had this type of behavior about 2-3 weeks ago. Very dangerous when I was crossing an intersection, pfff, it just stalled when I tried to accelerate! Well, I NEVER knew it was a vacuum leak until the day I pulled the SuperRam off...

 

As a Canadian maybe I'm missing something....what is Seafoam?

 

Ed, I think you can just disconnect the cold start valve.....just in front of the second to last injector on the drivers side. There may be a post on doing away with it in the tech tips. When you ohm the injectors, and come back with those numbers we'll know more...it maybe possible you have a sticky injector or one that is stuck open. Don't mean to be sarcastic, but get your digital voltage ohm meter, and turn it to the upside down U, put the probes into the injectors, do this both cold and warm as mentioned and write down the readings and come back with them..just trying to help you through the steps, you probably already know this but one can never tell. The pickup coil can be good but have a bad connection, that's why you wiggle the wires..load has nothing to do with it, vibration does.

Ed, I'm not a rocket scientist, and like you most of the cars I messed with and built were carb cars, but when I first joined the forum everyone ranted and raved about the FSMs, like you, I didn't know if I could follow them...but low and behold, it's very simple to follow...thank God for that or I would still be lost....and spending money on good parts. Good Luck Ed, once again, I hope I didn't come across wrong.

SeaFoam is a carbon remover, fuel system cleaner etc. And I know you have it in Canada. Take a look in the general section, I think there's a current post on it, great stuff.

 

If you ohm the CSV it will only read 4-6 ohms (normal). Different than the injectors. Just a tip.

 

Ed,
Just another "for what its worth" experience
1 ran good cold ( < 160 ) then warm stumbling ( not really a miss )
2 When stumbling occured, WOT responce was still good
3 When pulled into garage rich smelling exhaust ( not overpowering )
4 02/temp sensors, and injectors were good ( no CS injector LT1 )
5 decided to seafoam ... found exhaust leak during "smoke out"
6 fixed leak and stumble gone

 

I'm going to try the Seafoam myself.

 

Today I went and got some Seafoam, and on the way home I noticed a few nice looking Corvettes in front of an auto repair shop. I stopped to investigate, and found out it was a family business, Dad, sons, daughters, wifes all work there. It's a crappy looking place in the old part of town, and I never noticed it before. The dad came out to sell me a Corvette and told me that he buys and sells cars, and is now concentrating on Corvettes, and has been in the repair business for 30 years there. I expalined my sputtering when warm problem, and all that I had done so far. He suggested a scan and felt sure he could fix anything it might be. So I said go ahead. Everything checked out, injectors held at 42 psi, Aic, Tps, no vacuum leaks. Then he took off the PVC valve and said, here's your problem, too much blow by as I saw a steady stream of smoke coming out of the valve cover, he checked the other valve cover, same story. The scan showed a rich condition, and this is why. He suggested cleaning out the crank case with a crankcase cleaner,new oil and filter (20-50 instead of 5-30), Restore additive, and Seafoam through the TPI. He had it all delivered from the parts store (I paid) and his son did it all for a $10 rack charge plus $90 for the scan. It smoked like crazy. It was worth it not to **** off my neighbors. Very nice people, and the dad really really knew his stuff.
After they were done, the blow by was gone, no smoke out the valve covers at all! Only 2 little problems:
1. The son spilled a little crankcase cleaner on the hot manifold, and it went FUMPTTT, and exploded into flame, singing his hair and eyebrows. He grabbed the dry chemical fire exinguisher and sprayed everything. I was in the waiting room and heard it. I came out to see my formerly pristine clean car covered inside and out with white powder. I was really calm I can't see any damage. They took it across the street and had it detailed, for no charge of course, did a nice job too.
2. About 2 hours later I went to the store, ran great, came out, took off, no power brakes, took both feet to stop. Now it also runs a little funny like it has a vacuum leak.. I returned to the shop and he checked it out, power booster is shot. $149 plus labor. Is this related to the Seafoam? The Fire? Dad will see it tomorrow, gone for the day.
The brakes were getting harder and harder to apply before this, maybe carbon was all that was keeping it together?
I think I'm making progress, hard to tell some days At least I didn't buy new injectors when mine work fine, so I'm still money ahead. I love my Corvette. Never boring.

 

Great...if you've ever read posts about SeaFoam...you know I highly recommend it..good stuff!! as for your brakes..SeaFoam had nothing to do with it!!!! They only used a vac. line, detached from the booster, that went directly into the engine..not backwards, and your hard brakes were a sign your booster was on it's wat out.

 

Does this mean your problem is fixed?
Even when its warmed-up?