Vette70coupe

Hello Everyone.

This is my very first posting, so if my format is wrong, I apologize in advance. I have a 1987 Corvette Coupe with 39,000 miles. I bought the car in 2001 with 22,000, and in 16 years, I have only put 17,000+ miles on the car.

I have been having an erratic idle problem that comes and goes. There is no way to tell just when the car is going to act up on me. When it does, I loose all power, and the car runs poorly, it even backfires. If I put my foot all the way down on the accelerator when this is happening, it feels like I am running at 25% of power or less. I can drive the car for 30 miles and not have an issue, then all of a sudden, I will feel the engine running rough, and I either stall, of have to limp to the side of the road. This problem has happened to me when the car is ice cold or after its been running at normal operating temperature. I am not throwing off any engine codes when this happens.

At first, I thought that it could be dirty fuel-injectors. I tried a can of BG44K, the problem seemed to go away. Then out of no where, it happened again. A friend told me to change the ETC (Engine Temperature Control) Switch. I did and again, the problem came back. Next I had a Service Station look the car over, and they suggested a new computer. We did that, and again the problem came back. The Service Station also ran a fuel pressure test, and determined that my fuel pressure and pump were good.

I spoke with a cousin of mine that had a similar problem with a Jeep. He told me that one bad fuel injector can cause this kind of problem. He also had the issue of the problem coming and going. I took the car home with me this weekend, and dumped a can of BG44K in the fuel, hoping to drive the fuel injector clean.

Does anyone out there have an ideas on what could be causing this nagging issue?

Thank you in advance for reading my post.

Sincerely,
Bob K

Racecarfan17

Ohm your injectors. Should be somewhere around 16.5 give or take. These injectors are prone to shorting out. I found on my 89 2 injectors 5 and 7 shorted. With both on the same bank I believe it shuts down the injector driver on that bank and it ran just like that. Age more than mileage may be the culprit here

aklim

Lets leave it alone for now unless you want to just clean the TB. You will have to take the IAC off, take the top plate off and the housing. Clean all passages. At this time, it might be good to do the heater bypass so you don't have one more attachment to take off. Won't hurt

As far as I am concerned, the ECM is primitive and a code means something is FUBAR. I rely more on the ECM output to make a decision.

You have tried the snake oils, aka cleaner in a can, throwing parts at it randomly, etc. So lets try something along the line of diagnostics. We don't know what is going on so lets forget everything. Here is what you need to run that engine. Fuel, Air and spark. You have air so lets get the fuel and spark down. When you turn the car to run, it pressurizes for 2 seconds. It won't repressurize the next few times if you tried so lets be quick. Buy 3 things. Spark plug wire, spark tester and a fuel pressure gauge. Check fuel pressure by turning it on and seeing that the pressure rises and then turn the key off. See how fast it drops. Take the car for a Wide Open Throttle run. See how the fuel pressure holds up during the run. Put the plug wire with the tester on and run the car in a dark garage. It will run like crap but see if you get a blue flame.

First off, the snake oil may or may not clean anything. It is like cleaning a room in the dark. You don't really know what is clean and what isn't. You cannot clean a bad injector good. Do you know if the injectors are multec injectors or not? See attached pic.

When it is hot, see if it will light up in the dark garage if you spray a fine mist of water around the plugs. This tests for plug wires.

aklim

Problem with Multecs, if what I am reading is right, is that the ethanol eats the windings of the coils and they short out. They are too "high maintenance" for my liking having to make sure you never get any ethanol in the gas. There is only 1 place for a Multec injector. The trashcan.

Racecarfan17

aklim, That is my understanding also. Ohming only takes 10 minutes or so and either rules out a short or pinpoints one. I do agree quit throwing parts and diagnose.

antfarmer2

Mine did that on my 94 changed the front two O2s runs like a raped ape.

Bwbob

The MAF could very well be a problem. They can develope cracks in the circuit boards and can make for intermittant problems.

whalepirot

This can be a bugger; ask me how I know. My initial suspect was on the fuel side, with such low mileage, but your shop (hopefully competant) okayed that.
I believe the '87 is 'bank fire', which complicates electrical troubleshooting as a pinched wire affects one whole side of injectors intermittantly, and can be a bear to find. tis best to be able to check when the problem actually exists, of course.

Some chain parts stores rent test kits, like noid lights, to check injectors' firing properly and/or spark strength gizmos.

Heat-related might indicate a failing ignition module and good ones are harder to to find. I bought 3 for that reason.

Old school shops replace too many ECMs becasue they aren't current, don't understand new cars and the unknown is suspect in their mind.

Vacuum leaks from old hoses affect control device actuation. Are any cracked or poorly connected? When the engine is warmed up, all those sensors and activators control the engine, unlike when cold.

Are there any codes? What is the vacuum level and how do the plugs look? Those simple things, on an unmolested engine still apply. Corrosion of relatively delicate connectors is an issue, especially in wet and/or salty climates. DeOx can be your best friend to clean them, ensuring proper (low) current flow.

Absolutely>> diagnose, don't throw parts! It sounds complicated but much of the process is simple with some understanding of how it works and a logical approach. Is it spark or is it fuel, for starters.

Vette70coupe

Thank you to everyone that responded to my first question!!!

I failed to mention in my posting that I cleaned the Throttle Body (twice) and replaced the Idle Air Controller. I also reset the Throttle Position sensor, and the problem continued. I also put a new set of Champion Platinum Spark Plugs in.

I was fortunate enough to be in the area once when the car was acting up, and I was able to get it to the Mechanic that replaced the Temperature Control Switch and the Computer. He cleaned the Mass Airflow Sensor, but that didn't affect the way the engine was running one bit.

This theory of the Fuel Injectors shorting out sounds interesting. Where do I attach the OHM meter? Would I actually see any arcing if one or more of the fuel injectors was shorting???

aklim

How did you clean it? Did you take all the pieces off? IAC, IAC housing, TB top plate and TB off the manifold? Did you clean all the IAC passages and with the reassembly, use fresh gaskets? How did you adjust? What specific tools?

That sounds unfortunate that a mechanic replaced parts and didn't solve the issue. Hope you didn't have to pay for it. I'd be pissed.

If you are going there, unplug the plug going into the injector and run the DVOM on the terminals of the injector. Although I must warn you that this will give you an unreliable answer. IF the thing is out of spec, the injector is shot. IF it is within spec, the coil is good but the pintle could be blocked or partially clogged. Also the voltage is so low, you won't see arcing or sparks.

Railroadman

Is that what you meant to say? As written it means you are positive he would see arcing.

aklim

Whoops. My bad. To be corrected in 2 mins or less

Railroadman

aklim

Enough of that. Probably had one too many "cheer" last night and paying for it today

Edson Calegari

[QUOTE = Racecarfan17; 1594536907] Ohm seus injetores. Deve ser algo em torno de 16,5 mais ou menos. Esses injetores estão sujeitos a curto-circuito. Encontrei em meus 89 2 injetores 5 e 7 em curto. Com os dois na mesma margem, acredito que desligou o driver do injetor naquela margem e funcionou exatamente assim. Idade mais de quilometragem pode ser o culpado aqui [/ QUOTE]

Hi! my C4 has the same problem. managed to solve? how it was?

zeus_24

Hello,
I have an 89 with same issue, was you able to figure out the issue?

Thanks

altownsend

1990 C4 101K miles, Automatic

I have what I believe this problem as of today, May 2, 2022. The conversation dropped and I did not read what the fix was. Has anyone fixed the issue with losing power and can you post it here to give the rest of us a possible solution - thanks

altownsend

Possible solution:

I took a good look around under the hood on Monday. I checked the spark plug wires, vacuum lines, and anything that might look out of place. I was going to pull the plugs to see if any were burning 'funny'. During my troubleshooting exercise, I noticed, after turning it, that my distributor was loose. I was going to take the distributor cap off and have a look-see under it. I was able to easily turn the distributor with little resistance.

After guesstimating the timing, I tightened the distributor down. We used to guesstimate the timing by letting the engine run while slightly adjusting the distributor until the engine runs just right. Check the starting to ensure that the engine starts as expected.

I noticed three things after this exercise

1) No more hesitating or loss of power when driving/accelerating
2) The car ran better, overall, again, with no hesitation, no more loosing power while driving. that loosing power thing felt like the car had gone into limp mode.
3) Noticeable increase in performance. The car was sputtering when cold, and it was not performing strongly. After adjusting the timing, the car gets out of a dead stop stronger and faster and with more torque. The car idles more smoothly.