Hookdbyvettes

Hi, I have a few problems that started a month after I got my '86 Corvette auto(4 months now). Hard starts, a huge bog or total loss of power from a dead stop & ugly surge in power at 1/3 to 1/2 throttle from 1600-2200 RPM, the last 2 problems start as the engine heats up & is hot. All these problems started at the same time & have increased in severity together. I have found each problem listed apart, but not all at once. Each seems to have it's own possible cause & fix. Today I Googled the problems without putting '86 Corvette in front of it. I know I'm not supposed to lead the doctor, several sites suggested the O2 sensor as one of the most plausable causes for the 2 main power issues. Then I looked up most likely problem with a failing O2 sensor, which listed no throttle power on take off & surging power issues. I have read about the 9th injector & hard starts, though that problem did start with the rest of them. I'm about to throw a part at the problem, I ordered a Delphi O2 sensor. I tried to test voltage of the sensor, but never got it tested(that's a hot area). I have replaced the plugs & wires, checked the cap & rotor, followed all vacuum lines multiple times for cracks or disconnections & checked all the electrical connections I could reach (unplugging & plugging each one). If anyone sees anything obvious I've missed, please let me know. Thanks. (P.S. The car has 79,000.)

Kevova

Codes? I would be sure MAF is operating correctly. Do you have FSM? Google is not a service manual.

Hookdbyvettes

I don't have the funds for a manual now, but I can use the wire on A&B to find what's stored. The CEL light has not been on except when I start the car. I am replacing the master cylinder today, so I'll do both then. I'm not a young guy and I get winded quick in the Alabama heat, it's been running in the high 90's, as has the humidity. I'm soaked head to toe in 15 minutes. I'll do my best to pull some info so the experienced can give an opinion. Thanks.

Hookdbyvettes

So I used the A to B method & a code 12 was all I got. As I had said, the SES light never comes on except during starting, however never during the acceleration or surging problems.

Hookdbyvettes

Have a Delphi O2 sensor on it's way.

aklim

Try a run with the MAF disconnected and see if that cures the problem.

FASTAZU

You may also want to check your cats if your still running them, make sure they are not stopped up.

Hookdbyvettes

Ok, The SES light came on when I unplugged the MAF. I got back & read the codes: 22-Low TPS Voltage, 33 MAF Problems, & finally 36 MAF Burn Off.

Hookdbyvettes

I plugged the MAF sensor back in and pulled the ground to erase the codes. They did not come back, but my power problem never changed. I had a fellow that sold C4 parts only on wee bay, he suggested unplugging the TPS and see if the problem disappeared. It did not, but it didn't turn of the SES light either. I'm still convinced it's the O2 sensor, but keep the suggestions coming. I picked up a 7/8s sensor socket today. If the O2 sensor doesn't fix it either, the cats could very well be the problem. I'll have to remove all the felines from my exhaust.

aklim

Without a scanner, it is harder to see why you got a low TPS voltage. You will have to probe the 3 wires to the TPS. One will be 0 voltage, one will be 5V and the third will be variable from 0.54 to 4+ depending on how far you push the throttle in. That doesn't tell me what the ECM sees but that is the only way if you don't have a scanner.

IIRC, and I don't have MAF, there are 2 relays so swap them and see if the code changes after you erase the codes again.

Hookdbyvettes

aklim, I can go out and test voltages on the TPS if you think it will help but, it was unplugging the MAF that caused the codes to begin with. I have plugged the MAF back in, erased the codes and none have returned after driving it last night & today. I still have the same acceleration and hesitation problems. I will test the TPS wires, recording the voltage, it might reveal something else. Before I do though, my O2 sensor arrived in the mail and I've got to know if it had any part in these problems. If successful, this shouldn't change TPS voltage right? I don't know if it is important to note that it appears the O2 sensor has been replaced in the past. I've got to go the parts store, the tiny packet of anti-seize that the instructions said were included was missing. By the way, do I test the voltage of the TPS wires while the engine is running or just the ignition on?

aklim

It's possible the O2 is responsible somehow but I'm not seeing how. It could affect short and long term fuel trim but I thought it would not be considered when you do a WOT run? Some of the codes that came with the MAF removal are to be expected. Erase them and go scan later to see if they come back. The O2 generates its own current so I'm not seeing how it can affect the TPS.

What I am looking to see is if there is a dead spot somewhere. IF I have a scanner, I would see that the TPS rises evenly with no dead spots. No, it doesn't care when you test it. When the key is on in run mode, 1 should have 0 volts, one should have 5 and one should have 0.54V. I THINK your system has an adjustment but we'll talk about it later. Mine doesn't but I am a 91 and speed density.

aklim

After which, it might be a good thing to check the fuel pressure when the key is in run, how long it holds after shutdown and what it is at idle with the hose to the fuel pressure regulator off and finally, with the hose off and the nipple you took it off from capped and doing a WOT.

Hookdbyvettes

I checked again and still no codes after driving 30 miles round trip yesterday. I meant to tell you I'm not having WOT problems except, lots of pinging. Otherwise WOT is strong, it's accelerating from 1600-2200RPMs at or close to 1/3 pedal. At a dead stop(it's usually a big dead throttle) or 30mph(which is generally surging), those RPMs are my problem area and the WOT pinging is loud enough to tell it's doing harm well before it's heard, I can hear the damage (Pistons melting)!

Hookdbyvettes

Oh, I'm going to have to buy a fuel pressure gauge too.

aklim

First thing that bothers me is why you are having pinging. Knock sensor should have retarded timing. Is your timing correct? Using 93 octane? Is it running ridiculously lean? Are you having air leaks?

Hookdbyvettes

I purchased a fuel pressure gauge, idling in gear I've got 30psi. In my trouble spots 1600-2200rpm under part throttle situations it's fluctuating a lot but, it reads somewhere in the high 20's. Also I'm not having WOT acceleration problems, except the pinging and the power is way down at WOT, so the timing may be retarding, just not enough.

Hookdbyvettes

One of my headlights stopped cutting off when it hit the bottom, so I used a piece of advise I found here, pulling the **** out a tiny bit after the headlight closed, cutting the motor off. I found the headlight motor running on one day last week when I came out to go to work. Look at the pretty bolt that passes through the headlight frame. Of course this is for another post, but it's why I've been working on other issues rather than putting in time on the engine. Brass is king! Back to engine problems.

JrRifleCoach

^^ This^^

If the FPR is leaking fuel, then fuel pressure will not increase when the engine needs more fuel to accelerate.
This will be noted when the vacuum hose is pulled of the FPR and fuel is present.
Simple check requires no tools. Just be careful as those plastic lines are fragile after all the years of enduring heat.

Hookdbyvettes

My fuel pressure starts at 30psi, but fluctuates wildly when you step on the throttle lightly or full. It fluctuates, but I'm certain the pressure is not climbing. If anything it's dropping. I pulled the vacuum line from the FPR and there was no raw fuel in the line, however it does smell of fuel. How do I test it? I have a Mighty Vac hand pump to put vacuum to it if that would expose anything? I'd also say the dead spots are getting worse. A local mechanic said it sounds like an O2 sensor(I didn't tell him I thought the same), but I now believe the FPR has something to do with it too. Does anyone think both may be happening to fail at the same time? It could explain why there is no one simple answer to explain the symptoms.