I have a 91 Z28 with a 305 TPI. For some reason around 2500 rpm the car acts like it has a governor on it - full throttle, no power. I have replaced the plugs, plug wires, distruibutor assy, Ox sensor. The chevy place said that the timing is being retarded and giving a code 43 but that the knock sensor is good. This unit has the ESC incorperated into the ECM/EPROM. I disconnected the knock sensor wire to make it think that the sensor was good all the time. Still runs bad. It runs great for the first minute and a half then it falls apart. Chevy Service said it could be the ECM or the EPROM. This sort of symptom used to happen way up in the rpm scale when the car was going about 95 mph. Then one night my wife and I went out to dinner and by the time I got back it was running really bad. I took it to a local shop and they could find nothing wrong. They changed all the gas out and recirculated some kind of fuel system cleaner. The car really has never run right since that night. That's when about almost a years worth of changing things began. The car runs great when first started - about 1 1/2 mins. Then bad on acceleration. If I let it gradually build it seems to be ok (very gradually). If I throw the car in nuetral and rev it up it does fine - but when I load it with the road it stumbles all over itself. The plugs looked normal when I replaced them about 3 months ago. I just went out and pulled one to look at it again . It does not have much wear - there is a slight tan color begining on the end of the insulator where the center electrode comes out. There is a very slight, light power white color on the base of the other bent metal piece that connects to the threads.

I connected a voltmeter to the knock sensor and drove it down the road. When I turn the key on it goes to 12V. As I start the car it drops to about 4V until the car is started, then it goes back up to 12V. After about 15-30 sec it drops to around 1V stays there for a little while then goes back to 12V. It stays at 12V through out the RPM range and at all speeds. I shut it off to see if it would go back to 1V during that short time after it is started. It did it again, but then went back up to 12V. Haynes book says 8-10V. Is 12V too high? The car smelled like fuel when I got back. It has smelled that way alot. What is wrong with this car?I am so tired of replacing parts that are good. I'm going broke. Can somebody help me - please??

 

Check the resistance on all your fuel injectors. Mine were low and had the same kind of problem. It didn't throw any codes, but after the ignition was on for a couple of minutes, the low resistance from the injectors heated up the ecm and the car was not getting any fuel, which could cause a knock also. It didn't always happen, but it gradually got worse overtime. It also would not restart after the car had been running for a while. I am not sure if you have the same problem but is is another area to check out. If you think it is the ecm you could check the voltage coming to the fuel injectors.

Just remember, the problem has to be either fuel, spark, or compression. So start troubleshooting and good luck.

 

Well I just got a code 32 (EGR Valve) while driving home today. Can this be causing these acceleration problems or is this just another problem?

 

I would do a vacuum check on the engine. Although a vacuum leak should always affect the engine, not just a a certain time period. But anyways, it should have around 20 mmHg if it does not have any vacuum leaks, check the vacuum reading after it starts running bad. A good spot to take a reading is off the plenum where the fuel pressure regulator is connected to. Use that port. If the reading is low, disconnect and plug off your EGR port and see if that makes a difference.

 

It seems to be a lean issue from the sound of things. You could try disconnecting the wire from the EGR valve and see if that makes a difference, just a suggestion???

But do the vacuum test first, then disconnect the EGR, make sure you clear the trouble code before you start again (disconnect your battery)

 

Pellmanm - Thank you for your response. The vacuum line from the EGR valve goes to the EGR soleniod. If I disconnct that line I feel no vacuum coming from the solenion. When should there be a vacuum felt there. Is my solenoid bad or my ECM not working? I thought the EGR line should have vacuum on it anytime above idle???

 

The E.G.R. solenoid is designed to more finely control the E.G.R. valve. At Idle with the engine cold, their shouldn't be any vacuum present. When the car is warmed up though, the solenoid should not be grounded by the E.C.M., which means vacuum should be present. If the E.G.R. valves flow is limited to much, you will get spark knock. I would check the valve to make sure it isn't seized by pressing the diaphram in using the finger holes under the valve first. Sometimes they get seized, or plugged and don't work properly. I don't know of a way to test the solenoid, but that's how you can verify the state of the valve. Personally, I would change the valve, solenoid and oxygen sensor at the same time to eliminate the problem. The reason I added the oxygen sensor is because the E.G.R. valve usually wipes it out when it goes bad. The voltage reading from your knock sensor is 8-10v normally. The 12v you're getting more than likely means that it is sensing detonation. The E.G.R. system is more than likely the culprit for your spark knock, fuel odor and rough running vehicle. It sound as if your vehicle is getting the full range of problem created by the E.G.R. system. If the valve isn't seized, then your problem is centered around the solenoid. Before replacing the solenoid though, I would check your wiring to make sure you don't have any rotted wiring that's causing the solenoid to work improperly. I hope that helps you get the problem fixed.

 

I am having the same problem with the code 43 on my 92RS 305 TBI. After searching the boards I found its a common problem with many possible causes. I know if the ECM senses a runaway knock or no knock code 43 will trip and timing is retarted to save the engine. Under load or when the engine is warmed up the ECM will try to force a knock to test the system. If it can not get a knock the code 43 trips. Get it on a scaner and check the knock count and other sensor readings. Try a search with key words: code 43, knock sensor. Best of luck

 

I checked out the EGR solenoid. I disconnected the ECM wires from the solenoid and measured 12V across the wires. With no wires connected, I can blow air through the solenoid. I measured the resistance of the solenoid coil. It measures 0 ohms - I thought I read in the Haynes manual that all solenoids should be above 20 ohms. It also said that with the key in the ON position the solenoid should be energized. So, I hooked it back to the ECM, turned the key on but could still blow air through it - it should have closed then - right?. So it must be bad, or the ECM output gets loaded down when the solenoid gets hooked up. I can't check the voltage with the connector hooked up. I took the plenum off to inspect the EGR valve. I can't move it by hand but I can put a tube on it and move it with a vacuum by just sucking through the tube. the first time I did this it got stuck in the vacuum applied position and I had to tap on it with a hammer to get it unstuck. But I can move it up and down if I don't apply too much vacuum but it is sort of hard to move. Is this normal. I was going to take it off and clean it but the bolts weren't budging. I sure didn't want to break one off, so I'll let the chevy place replace it if it still runs bad after I replace the solenoid . Any thoughts????

 

Replace the valve, solenoid and oxygen sensor. Your solenoid probably went out first, which left the valve at the mercy of the exhaust gases for all that time. Now the valve is so clogged with junk that its actuation is very questionable. When the valve quit working properly, it more than likely wiped the o2 sensor. If you replace all three, your problem should be fixed. Unless the autoparts store gives you a faulty part. Don't laugh at that statement. I had to take a replacement distributor back to autozone 3 times before I got one that worked properly and fixed my problem. Hope that helps you out.

 

I believe it - I had the same problem with an Alternator. I just replaced the Ox Sensor last week. Do you think it's bad already?

 

If it's that new, I'd say you should be fine. Just get the other two problems taken care of A.S.A.P.