No Acceleration

[Corvette Emma]

Just some History:
This past fall I took my corvete (1989) to Ocean City Maryland for Corvette Weekend, it was great. On the way down my car drove funky cause it didn't want to accelerate and it would fall on its face at around 3,000 rpm. I thought it was starving for fuel so I topped the tank off but it acted the same way. While we were at the ocean, we stopped at a local watering hole for a couple of hours and when we came out, the car wouldn't start. I didn't know what to do. I pumped the gas, I let it sit for like 2 hours but it still didn't start. We caught a cab to our hotel and would deal with the issue in the morning. We went back to the car in the morning and the car started. I didn't shut it off until we got back to Baltimore, Maryland. I thought the problem was the fuel filter. Today (12/22) my friend and I replaced the fuel filter. On my way to my friends garage the car ran great. This is one of those classic "INTERMITENT" problems. We replaced the fuel filter and on the way home the car ran the same way as Ocean City Maryland. The car fell on its face around 3,000 RPM and felt like the car was running on 4 of 8 cylinders.
PLEASE SOMEBODY HELP ME!
Thanks,
Lee

 

[Fast Freddie]

since you have already swapped out the fuel filter, i would suggest you get a fuel pressure test gauge on there and see if you have the right pressure. probably 40-50 lbs, im not near my reference material so you need to verify that. also, if you can safely do a fuel pressure test while driveing, make sure you have the right pressure under load. if all that checks out ok, have an exhaust shop check for a restricted exhaust. if all that fails then the car is ready to be junked out and i'll give ya $500 for it.. lol..

 

[gmjunkie]

My book says 34-39 lb fuel pressure for TPI 85-91!! Checkout the EGR valve too,there bad to get a chunk of carbon in them!

 

[Corvette Emma]

since you have already swapped out the fuel filter, i would suggest you get a fuel pressure test gauge on there and see if you have the right pressure. probably 40-50 lbs, im not near my reference material so you need to verify that. also, if you can safely do a fuel pressure test while driveing, make sure you have the right pressure under load. if all that checks out ok, have an exhaust shop check for a restricted exhaust. if all that fails then the car is ready to be junked out and i'll give ya $500 for it.. lol..

Freddie,
I would like to junk it for a C5 but I only have 18,000 miles on the OD. I will check the pressure. The car acts crazy like I am hitting a rev limiter. Thanks for the quick response. Lee

 

[tonylong]

btt
cuz i'd like to learn the answer so I'm ready when my 89 decides to get cute. If bad behavior is related to then the car warms up - check the ignition systen (esp the cap) by looking in the engine compartment in the pitch dark to chk for leetle sparksies. My cap had a hairilne crack that didn't show until everything was warmed up. Caused some weird stuff too.hnoes

 

[John Robinson]

Pull the codes. It may be that you have a bad knock sensor and the car is going into the limp home mode. Also check the knock sensor wires I hate to say this but with the age of the car and the low milage you may have had a mouse family living under the hood chewing the wires.

I am including a short article that I think explains the bad wire theory.

Knock Sensor

​

A quick look at “spark-knock” fundamentals.

For the record we will say that the knock is a non-regulated quick rise in pressure generally confined to a pocket in the combustion chamber.

Now let us see if we can find out how this “quick rise in pressure” occurs. There are a number of ways but we will only mention two. One is a hot carbon spark setting off the mixture generally in the squish area of the head before the piston reaches top dead center of compression. That is rare these days.

The second would be low octane gas that ignites spontaneously at a low compression pressure. Even in today’s world of good grades of gas there are some combustion cavity shapes that are better than others so if one got a poor tank of gas knocking could come into play.

This quick rise in pressure from a sensor standpoint produces in the sensor a quick rise in both resistance and voltage. But the voltage can’t rise beyond the fixed ratio of the number of turns in the coil between the low voltage side and the high voltage side therefore the sensor can only sense a rise in resistance.

The ECU has a program to sense the rise in resistance from normal piston motion compressing the mixture. Anything below max RPM piston velocity will not trigger the knock sensor. But if a very quick rise in pressure from a knock occurs the sensor will sense both the rise in pressure and the resistance to the spark across the spark plug gap.

Even if the knock is not audible the sensor will indicate knock has occurred.

Now a loose wire will also be sensed as higher resistance to the battery voltage to the sensor. Its only way of telling you that something is wrong is to tell you knock has occurred. If there was a loose wire program it would indicate “loose wire” but since there is no such program it can’t tell you exactly what is wrong.

With this in mind a code H43 which is a knock sensor code may not necessarily mean the sensor is bad but rather a wire is loose or broken.

Author:
Leonard A. Karber

Please let us know what you find

 

[Corvette Emma]

Leonard,
I have two quick questions:
If I'm not getting any "Check Engine" dash alarms, will there still be trouble codes.
If there are trouble codes to get, what type of trouble scanner do you recommend for the Do-It-Yourself type.

Thanks,
Lee

 

[Fast Freddie]

not sure about an 89 vehicle but SOME will store codes that dont turn on the CEL. about any auto parts store ( o'reilly, autozone, advance, etc...) will read your codes for you.

 

[WhalePirot]

There can be intermittent codes: the car 'burps' a code, but the check engine light goes off. The code remains set, until the ECM is reset.

I pull codes with a paper clip, shorting #1 and #2, I believe. I like to reset the ECM and see if they recur before going nuts on troubleshooting. Always, check the basics anyway, like arcing along the plug wires, unplugged hoses or wires, leaks, etc.

I am wondering if the cat might be plugged with the RPM limitation. If that mileage is true, it is more likely a fuel filter issue. Did you change both filters?

 

[Corvette Emma]

There can be intermittent codes: the car 'burps' a code, but the check engine light goes off. The code remains set, until the ECM is reset.

I pull codes with a paper clip, shorting #1 and #2, I believe. I like to reset the ECM and see if they recur before going nuts on troubleshooting. Always, check the basics anyway, like arcing along the plug wires, unplugged hoses or wires, leaks, etc.

I am wondering if the cat might be plugged with the RPM limitation. If that mileage is true, it is more likely a fuel filter issue. Did you change both filters?

Great, I didn't know the car had two filters. I changed the one filter behind the passenger front wheel. Where is the other?
On my way to my friends house the car ran great, after the filter rplacement, the car ran like sh**! I never noticed before but when I put my hand by the exhaust pipe, one was blowing out and the other one had nothing. I don't know if this has anything to do with it or not because I've never noticed the exhaust thing before. Just to make it clear, the driver side and the passenger side exhaust is blowing out but each inboard pipe has nothing coming out. I didn't see anything in the manual about this as if it is something like at wide open throttle the other exhaust pipe kicks in. Does this exhaust issue sound normal?
When my neighborhood mechanic opens after the holiday, I was going to have him pull the codes but until then I will check whatever you guys can think of.
Thanks,
Have a Happy Holiday,
Lee

 

[gw962]

Lee,
I'm not sure on an '89 but my '90 only had one working outlet on each muffler. I think this was a GM fix for noise and resonance, so you may not have an issue there.
Pulling codes is relatively easy if you don't want to wait. Do a search and I'm sure you'll find a diagram showing the ALDL connector and which terminals to jumper.
The suggestion to go to AutoZone or Advance is also good for a quick check.
Good luck and Merry Christmas.

 

[WhalePirot]

The exhaust is normal and a few threads here talk of the 4 outlets, two real, mufflers.

The second filter is in the gas tank, on the inlet to the fuel pump. It is a screen type and is found when the fuel pump is pulled; not a terribly difficult exercise. I recall the bolts on the collar, which mounts the fuel pump assembly to the tank, as 10mm. The pump comes out through the fuel filler door.

To illustrate how difficult (not) this is, I did this once, in a parking lot at DMV, after my car would not stay running due to a broken hose inside the tank.

 

[Corvette Emma]

Lee,
I'm not sure on an '89 but my '90 only had one working outlet on each muffler. I think this was a GM fix for noise and resonance, so you may not have an issue there.
Pulling codes is relatively easy if you don't want to wait. Do a search and I'm sure you'll find a diagram showing the ALDL connector and which terminals to jumper.
The suggestion to go to AutoZone or Advance is also good for a quick check.
Good luck and Merry Christmas.

I checked the Engine Codes and came up with only the 12 code which is normal. I will see if the neighborhood mechanic can check the fuel pressure for me. I'm getting close to throwing in the towel and either letting a real mechanic look at it or just dropping a crate LS7 in (lol).
My wife thinks I'm crazy playing with my baby this late on Christmas Eve but what can I say, I love my VETTE!
Merry Christmas,
Lee

 

[jmccloud]

Poor high rev performance

Your symptoms sound like either a plugged fuel filter (but you've already replaced it) or a plugged cat. My experience is that a plugged fuel filter is steady bad performance but a plugged cat gives very sporadic performance. Sometimes great, sometimes poor at higher revs (like 3000+) and other times the car won't even start.
So I'd bet on plugged cat(s). My diagnosis was to take it off, gut it, put it back on and car ran great. Bought a new one to pass emissions. Lot of work.
A more sophisticated diagnosis can be done with a vacuum gauge if you know how (Poor vacuum at high revs and partial/full throttle) but it's a little tricky if you don't know what 'normal' vacuum at a particular rpm/throttle setting should be.
Hope this helps

 

[Corvette Emma]

Your symptoms sound like either a plugged fuel filter (but you've already replaced it) or a plugged cat. My experience is that a plugged fuel filter is steady bad performance but a plugged cat gives very sporadic performance. Sometimes great, sometimes poor at higher revs (like 3000+) and other times the car won't even start.
So I'd bet on plugged cat(s). My diagnosis was to take it off, gut it, put it back on and car ran great. Bought a new one to pass emissions. Lot of work.
A more sophisticated diagnosis can be done with a vacuum gauge if you know how (Poor vacuum at high revs and partial/full throttle) but it's a little tricky if you don't know what 'normal' vacuum at a particular rpm/throttle setting should be.
Hope this helps

I will look into the catalytic converter as being the problem based on what you (jmccloud) are saying and my experience today. It just so happens that my car was due for emissions testing before Jan. 08. I started the car this morning (Friday, 12-28), let it warm up and melt the ice on the windows, and take it for a spin to see how it was going to run. As I was idling through the neighborhood I could tell by the exhaust sound and throttle response that it was going to run like crap at wide open throttle. Getting through the neighborhood and to a nice straight away I punched it. At first it kind of stumbled then poof, ran like a bat out of hell. I was keeping my fingers crossed that it would hold up for the emissions test. It passed the emissions test so this has bought me some time to decide what kind of exhaust system to go with. I will explain to the exhaust shop about the issues with how the car has been acting to see if they agree with cat problem. I will keep you all informed on how this turns out. I hope this fixes the problem, if not I'll have a nice new exhaust system but still have a corvette that won't break the 3,000 rpm barrier.
Thanks everybody for great conversation and if you have any exhaust preferences, please reply.
Lee