OK guys. My 87 GTA (350 TPI/700R4) is driving my nuts. Here's the deal... I was driving along just fine and all of a sudden I noticed it felt like it was surging while under normal acceleration. At the next light I noticed the idle was lower than usual and rough (it is rough both cold and hot, BTW). The exhaust smells rich. When accelerating, the car shakes. I have not gassed up lately so it can't be that I got bad fuel. Here is where my diagnostics are at:

NO CODES

We did some data logging and nothing seemed out of the ordinary. As far as the ECM is concerned all is good, although the software did see a "32" twice during the logging period. Again, no codes were set.

I have changed the plugs, rotor, and pickup coil. The ignition module was tested and is good. The cap is virtually new, as are the wires. The timing is rock solid 7*. Injectors test good (ohm'd out between 16.8 and 17.1) - also when the car is running I pulled each one and they all affected the idle, so they are all apparently working fine. Replaced the coil, and the EGR valve and solenoid. I unplugged the MAF and it didn't help matters. I can't find any kind of vacuum leak.

If anyone has any other suggestions, I am all ears. Since there are no codes it has to be something fundamental like a dead (or dying) cylinder, but killing off one by one (via injector and plug wire) only makes things worse.

Please help!!!

TIA

Eric

 

Rough running and rich exhaust are consistent with a fuel leak. Check the FPR to make sure there is no fuel leaking through the vacuum line to the plenum.

Is your oxygen sensor active?

 

Hmm... that's an interesting thought. When I pulled the plenum off to change out the EGR valve, there was a very strong smell of gas in there. I thought that was unusual. Actually, there is a smell of fuel just generally permeating the engine compartment, something I haven't had before.

What is the best way to check the FPR? I mean other than just looking at the vacuum line?

I was also thinking about the evaporative fuel canister setup - could a problem there manifest itself in the types of issues I am having?

The O2 sensor is working fine, according to the datamaster logging.

Thanks Vader!

 

OK, I finally got around to doing some more work on this thing. I got a fuel pressure guage and found:

Key on (not running) = 43-44 pounds
Running (idle) = 36 pounds
Stab the throttle and it jumps momentarily up over 40, may 44
Pull the FPR vacuum hose (idle) = 44 pounds
Turn key off = 43 pounds - holds pressure for a long time

The vacuum hose to the FPR smells like gas.

The symptoms again:

Rough idle, smelly exhaust, surging on normal acceleration, shaking under hard acceleration.

Replaced plugs, ignition pick-up coil, rotor, cap, wires, EGR solenoid, tested ignition module, swapped EGR valves, swapped igition coil.

No codes. Datamaster scanning reports all sensors, including O2, working optimally.

So, am I looking at a bad FPR???

I am at my wits end here! Please help!!!

 

Your fuel pressure readings seem very normal. If you remove the vacuum line from the FPR with the engine running, any leakage through the regulator should be readily apparent.

The fact that the pessure holds after shut down would seem to indicate that neither the regulator nor the injectors are leaking, however. I'd be looking at the oxygen sensor again, and make sure there are no air leaks in the exhaust either ahead of or near the O², and that the AIR pump and valving are not supplying air to the exhaust manifolds once the engine is warmed and in closed loop mode. Any extra air admitted there will tend to make the O² readings artificially lean, and the ECM would attempt to compensate with more fuel until the O² is satisfied. That, of course, would make for a rich condition in the real world, why the O² would only be reporting a normal EGO level to the ECM.

 

There is no obvious gas leak from the FPR with the hose off, engine running.

Well, the 02 sensor readings are good - it's switching like crazy. But that only means that things "may" be OK in the left exhaust. It is possible I suppose that the right (passenger) side may be giving me grief. Mind you, if that were the case the ECM wouldn't know to change anything.

The AIR system was removed long ago. The headers have the AIR tubes on them, however, and I had to cap them off. It could be that the method I used finally packed it in and it is sucking air into the header on the passenger side. All I did to cap the air tube was use a chunk of heater hose, clamp it on the AIR tube, and plug the end of the hose with a big bolt (hose clamped on). It has been (or seems to have been) fine for a few years, but who knows?

I will check it out tonight.

Thanks

 

Valid theory. Air leaks can dilute the exhaust gas and create an artificail lean condition.

Another thing to consider is the condition of the O² sensor. The typical failure mode of a zirconia oxygen sensor is to produce a decreasing signal as it nears the end of its life. Provided the signal is within the acceptable range allowed by the ECM, the ECM will rely on the data and adjust mixture accordingly rich until the sensor produces the correct signal. If your sensor is more than 30,000 miles old, or has been contaminated by oil, antifreeze, lead, incompatible RTV gasket sealants, or some other fuel additives, that may be part or all of the problem.

 

Well, the AIR tubes on the headers are capped off as good as ever - no trouble there. The O2 sensor is quite new, with only 2000 kms on it. All sensor readings look good, and of course there are no codes. I guess I could pull it off and have a look at it to see if it is munged up.

Failing that, I have no idea what to do. Do you think it could be a problem with the distributor? If I had weak spark that would cause a rich exhaust, no? I know the coil is good, as is the ignition module, pick up coil, cap and rotor, but could the dist itself be crapping out? I noticed when I had it apart to change out the pickup coil that one of the little magnet pieces on the "star wheel" was broken so I glued it back on. I can't know if I broke it (trying to get the rotor off) or if it was broken before I pulled the dist.

I am ready to set this thing on fire.....

Sigh.....