JamesRS

Help.......

I have a problem with my 84 cutting out at constant speed and under hard acceleration. In attempts to correct this problem I have replaced and tested several sensors and other items and I don’t want to just keep throwing money at it.

The car starts fine and idles well. The problem starts when I accelerate. Whether I accelerate gradually or aggressively the car will miss and stumble all the way up to the 5000rpm shift points, but the missing tells me there is definitely something wrong.

My troubleshooting method was to visually check, test, and then replace the items listed below one at a time. Here is a list of what I have replaced and tested so far.

New Cap and Rotor. (Tried a completely different distributor, same problem)
New plug wires and plugs (Plug wires routed correctly to avoid arcing and crossfire)
New TPS, adjusted to .525, then .540 – same problem
New MAP sensor
New O2 sensor
New ESC Module (Only code ever thrown was 42, so I changed this module)
Throttle bodies re-bushed and synch’d (this really made the idle smooth)
Knock sensor tested and unplugged – same problem
Replaced ECM prom with performance prom – same problem re-installed factory prom
Replaced all vacuum hoses
Valves adjusted and re-adjusted (desperation setting in)
New Fuel pump and filter (Pump from 85, set to 14PSI)


I don't know where to look next. Help please......

hugie82

Thats funny I was just doing a search on TPS sensor because my 82 crossfire is doing the same thing!!!
Now if the TPS is good theirs only one place to go I think-----the distributor, I have had older cars with alot of miles and the bearings in the distributor ware out and mess up the points gap from the shaft moving from side to side. I know we don't have points but we have pick up sensors for spark and injection pulse. I just don't know how to test the dist. without replacing it and we're talking $200+ for a new one!!! SOMEBODY KNOW HOW TO TEST???

CFI-EFI

Besides points, your distributor doesn't have any bearings, either. Just for yuks, both of you guys, try pilling the vacuum hose off the EGR valve and plugging the hose. Then go for a ride. Any better?

For the TPS, other than the closed throttle setting, make sure it goes to something over 4 volts at W.O.T. and check that the voltage climbs slowly and smoothly as you slowly open the throttle.

RACE ON!!!

JamesRS

Thanks for the replies guys,

CFI-EFI, I will pull the EGR vacuum on Saturday and let you know the results.

hugie82, I tried a new distributor on my 84 to see if it would correct this problem, but it did not. I have since put the original back in. My car only has 61,380 miles on it so the distributor is in pretty good shape. (in terms of bushing wear.)

corvette_bob

Sorry you're having so much trouble. While I'll NEVER be accused of being a good trouble shooter, try looking for loose/broken/shorting wires coming to/from the distributor. Also, try looking in the distributor for any sign of loose, shorting components. ( It's worth a try, and FREE).
Next, go to the injectors themselves. I know the throttle bodies were massaged, but what about the injectors themselves? Try taking them out and having them manually cleaned. I'm not sure where you live, but I go to a diesel injection service to get injectors cleaned, both for TPI and when I had my TBI truck. While you're in there, give a good look at the connections to the injectors and their harnesses. Look for any loose connections and/or bare/shorting wires. For cleaning the connectors under the hood, try going to Radio Shack for some "tuner cleaner". It's pretty much just alcohol in an aerosol can, usually with a tube for direct spraying. Personal experience has shown this stuff to work WELL for cleaning electrical connections.
These electrical gremlins can drive anyone crazy, if not to the poorhouse. Be patient, and when you find it, most likely it'll be something stupidly simple to fix. Again, personal experience.
Best of luck.

hugie82

Thats what I meant to say (DUH). My vette has @100k miles and I'll try the EGR test. I tested the EGR by pushing up on it when running and it spuddered then stopped once I let go. I'm going to put a voltmeter to my TPS later today.

CFI-EFI

As a word of explanation for the test, my EGR valve return spring became weak over the years. When The ECM signaled to open the EGR, it opened, too far, too soon. At low speed cruise, I had a lean misfire. You could feel the engine miss. It's a free test, so if it isn't the problem it isn't like throwing money at it.

RACE ON!!!

samsonb

I'll have to look into this. My 89 Vette drives ok. But I've noticed when I've been on the freeway going 70-80mph, and I hit the gas pedal, there will be a brief rumble from the engine. I can hear it and feel it. Does that sound like a miss?

CFI-EFI

I don't know from that discription. A rumble?

RACE ON!!!

JamesRS

Problem solved.

I tried the disconnecting the EGR like CFI-EFI suggested, but unfortunately that didn't correct the problem. I was going to hook up the computer and do some more logging but decided to look into the injectors first. The injectors looked clean at the filters and seemed to be working fine, but the car seemed to be running a bit rich. I checked fuel pressure, and it was set to 14PSI. I reduced fuel pressure to 11PSI and that corrected the problem.

I ran several tests on the car after reducing the fuel pressure and the results were that it idles smoother, accelerates without stumbling and doesn't have the overly rich smell at idle. Took the car for a 80 mile drive today and it ran flawlessly.

corvette_bob

Congrats

samsonb

I guess I could call it a vibration. I can hear it and feel it. When I'm going top speed and I hit the gas, I get a vibration from the engine.

I figured it might be missing briefly when I hit the gas at high speed? I plan on changing the spark plugs, so I'll see if that does anything.

ineVETTEable

Is that a stick or an auto?

samsonb

auto

ineVETTEable

I would take it out of OD and just leave it in DRIVE and give her. I suspect the trani is not down shifting as quickly as it should. This could cause the engine to rumble a bit as it trys to build R's, then down shifts and takes off. I have a simular problem with my Stang. This may also help eliminate the trani as suspect.

samsonb

Ok, I went out on the freeway in D, and it didn't do it. I traveled back in OD and it did it.

So, what does this mean with the tranny? Is it on it's way out? Would a flush fix this? Or maybe an adjustment?