Rauch

Just got an '87 Trans Am GTA last week and it has a *supposedly* rebuilt 350 out of an '88 Vette with 3,000 Miles on the rebuild.

It is definitely running rich. The exhaust fumes smell like gas and when idling in the vehicle, I can get a whiff of it as well. I pulled out a plug and it looks fine, didn't check the others as these things are a pain in the *** to get to. The threading of the plugs had what appeared to be oil to lubricate the threads, but the tips were dry.

The car failed emissions two months ago with outrageously high readings, but I have no idea where to start to fix the issue.

On the TSI Idle test, it received an HC ppm reading of 2,123 and the standard is 220. The CO% was 7.11 and the standard is 1.20. At high idle, the HC ppm reading is 868 and the standard is 220. The CO% was 10.51 and the standard was 1.20. The MAF was replaced a few weeks ago and I haven't taken it through emissions because since I've got the car, with the new MAF it is running what smells to be VERY rich.

It also failed emissions for the gas cap gasket, but I cannot seem to find a replacement cap the fits. The replacements I've found has wider space between the threads, and mine has a thinner space between threads as well as more threads. I've tried to find one in Autozone and Pepboys that would match up, but I can't find a matching thread.

Could the bad gas cap cause it to be that much off? I don't think it can, but I am not certain.

I've thought it was perhaps the plugs, but the one that I checked was fine other than the fact that it was some Bosch +4.

Anyone have any ideas on what it could be without having the need to replace virtually every part and perhaps not even fix the issue? I'd rather not take it to a shop and spend $100's of dollars for what could be a simple fix.

90vertiroc

With that high of readings u should first ck to see if it still has the cat setup on it? You didnt say if it is running well otherwise (idle, misses, power, drivability, etc.). Beyond that there are lots of things it could be.

bad injectors
wrong injectors
FP
timing
wrong ecm (from the swap)
bad ecm
o2 sensor
cts
etc.

For the folks here to help, youll need to have a good overall understanding of the engines systems, the evident will to do it yourself, and more detailed info.

However, there is a WEALTH great of info on here. Try using the search to glean thru the post for info on issues like yours.
thats my

Rauch

Thanks for the input . I could've sworn I posted more info in it, but I guess I didn't.

The cat is still in tact nor is it hollowed out. The exhaust system appears to be new and installed very well. No exhaust leaks anywhere and cleanly put together.

At idle, the engine feels a bit strange. Every so often, as if on cue, it'll shake a bit more than normal. I'd say every 5-10 seconds it tends to shake a bit more than normal. Almost like it is missing, but I can't be too certain if it is. A miss would happen more often, I would think.

I'm not sure how much power this thing should put out as it's my first V8 haha and first domestic on top of that. But my roommate was explaining to me that this fuel issue could be wasting some power.

Driving at low RPM's and low speeds it appears to be more rough vs. driving at higher rpm's and higher speeds.

The only thing I can really think that would point to a cause would be how the engine acts during idle. It goes from what would appear normal to something more erratic for a second or too and than it will settle back down.

Overall, it's really hard for me to pinpoint the issue when driving on squared tires, blown front shocks, a rubbing header, and heat shields that love to vibrate. If it wasn't for all that, I'm sure it'd be easier to diagnose.

Rauch

Hm...

I did a little research and through another forum I found the guy I bought the car off of as well as the guy that he bought it off of who had it for numerous years.


"Black on Black, 90something Corvette 350 ported out and race prepped, with a TPI injection system on it, headers, and cat-back exhaust, WAIT NO, there is NO CAT, (not legal) but oh well. Black Bart rims with beefy BF Goodrich radials, digital gauges etc (Not running right now, need to install new fuel delivery system, pump, and sensor) but this car is REDICULOUSLY FAST...dont have any real good photo's, only these for now.. -- pics are wfrom in the garage on jackstands ...and because nobody has time to work on the BEAST, its dusty and covered in gstuff (for now)"

"also, i recently got the GTA running, ran new wires to the coil, and some distributer work, vacum lines, lotsa wiring issues too... it runs really rough, stalls and sputters too, has minimal power, the high perf. M.A.F. that was in the car was accidentally thrown out by my dad, so we might need tog et the ECM PROM re-retuned...we will see,"

Now the car has a cat as well as edelbrock shorty headers, y-pipe, and a hooker exhaust.

Would simply upgrading to back to a high-performance MAF fix the issue? Or would I be better off grabbing a new ECU for the car?

When looking for an MAF, should I be looking for a TA one, or perhaps one that would match the Vette? I'm not sure of the exact year it came from other than what I've been told/read.

However, I do know the casting marks if that helps... (All I've found was it was 86-up, 2 or 4 main cap bolts, Canadian) Perhaps someone has greater knowledge and can pick out exactly what it is.

Block Casting - 10054727
Head Casting - 14102193

90vertiroc

90+ should not have the maf system, they used map (speed density) system until sometime after 92.

I believe all oe 86-89 tpi mafs are the same if not someone correct me.

If u knew the make n model of the old maf u mite luck out and the prev owners prom "tuning" could still b in line. But the maf is not going to b the sole fix for your probs.

If the prev owners hav been tuning the prom there is no telling where your at on any of the systems, unless your big into prom burning.

Rauch

I ended up messaging the guy on the forums and am awaiting his response to try and find a fix for it. From my understanding, he didn't have it tuned, but the original owner did.

I may just end up buying a inspection sticker and say forget emissions. I just want this car to run smoothly . But at the same time, I'm trying to learn what I can. I just wish fixing it was as simple as replacing plugs or an MAF. Maybe it is, who knows. I'll find out this weekend but am in search of others opinions as well

Rauch

I pulled a plug today and it appeared to have oil, or perhaps unburnt fuel on the threads. I'm not too positive what it could be nor am I sure why it could be happening.

There is, indeed, a misfire occurring. I cannot tell what cylinder it is coming from, but it exists.

That, with the smoke from the exhaust and the rich smell of the exhaust is leading me to believe there could be major engine issues. =/ Ones that I'm willing to fix, but I just don't have the time or money to do it.

I'm thinking it could be either the injectors (I felt them and they were all pulsating the same way, so I don't think it is them.), a head gasket, valve guides, or something else.

Now, if this car was tuned, as I believe it is, it could be looking for things that aren't there, causing the rough running of the engine. Maybe I'll try replacing the ECU along with a tuneup to see if that helps.

I'm just really worried about the oil and/or fuel on the plug threads. I also notice a faint gas aroma in the oil.

Rod Behring

I'm pretty sure those heads are TBI swirl-port. An 88 vette would have aluminum 113 casting heads. F-body TPI 350's had cast iron #083 heads.

Rod Behring

If those are TBI heads your timing might be over-advanced because TPI are set at 6BTDC and TBI engines are set at 0BTDC. The heads are the reason for the different base timing settings , not the induction. This could be causing pre-ignition which would make the ECM go into limp-mode which would cause it to add fuel and run like crap.

rvega022

Have you tried replacing coolant temp censer? I was having a similar problem with a 305 TPI engine. It was always running rich. I replaced the censer now the car runs great. with a bad censer the ECU thinks the engine is cold all the time and the part only costs about $15.

90vertiroc

Rod's info could explain alot, back off that timing and see.
The CTS might be a contributing factor if bad, the ECM will richen a cold motor, but not to the levels your seeing. You can check the CTS with a vom. Here is the chart: https://www.thirdgen.org/forums/atta...mp-tempse1.gif

Rauch

Hm, I'll check that out right now vert. I was planning on adding a new CTS but they were out of stock the other night. I do know that the engine is running quite cold, around 160-170*. The fans are permanently grounded to the point they run in auxiliary. I think perhaps even the tstat could be one of those failsafes and stuck open. Will definitely check it out this weekend when I try to find some headers for it in the junkyard... Hopefully I'll find a T/A, most likely not though. I may try and get them used on the forums if worse comes to worse. The passenger side one if big to the point it's rubbing and vibrating against the chassis.

Rod, That could be a possibility. Would I have to chip the ECU to fix that, or is there a simple way that I can adjust it?

I also realized there is no O2 sensor in the vehicle which could also potentially cause this to happen. I have to get one of those Bung's and have someone weld it and see if it helps.

Shadygrady

iTrader: (3)

If the car has edelbrock headers it should already have an O2 bung on them.Driver side in the collector.

burnout88

Is the check engine light on and what codes are you getting?

InjectorsPlus

iTrader: (1)

All good points. Also, the temp sensor on the front of the maniflold will create a rich condition if defective and there's no code for that.

InjectorsPlus

iTrader: (1)

Maybe it never leaves closed loop. Possible he needs a heated O2 sensor.

Rod Behring

Setting the base timing is done by turning the distributor with the EST wire disconnected. Under technical articles on this site is a good write up on setting the timing.
I had a car fail emissions badly because someone put a 160 t-stat and the engine didn't warm up enough to go into closed loop. If your fans are wired to come on with ignition this could be a contributing factor. Like the others have said, a bad CTS could do this as well.

It might be a combination of things, but hang in there you will get it. There is a ton of info on this site and a lot of knowledgeable people to help you.

Rauch

Ah okay, I found it, I just saw this metal wrapping welded around the header with a circle for it, so I just figured it didn't have one. But, once again, I was wrong haha.

No, there's no check engine light on. Just that stupid system check telling me somethings wrong with the right lamp when it works fine.

Ah okay, I'll check the resistance and see if anything is outta whatck with that. Which temp sensor are you referring to though, I'm assuming the CTS?

Hm, perhaps that's it. I'd say the O2 Sensor is approximately two feet from the headers. I'll have to read into open/closed loops and see if anything comes up.

Alrighty. I always thought turning the Distributor was for Carb'd engines only haha.

burnout88

Check the ECM for codes.

InjectorsPlus

iTrader: (1)

Two feet off the header, I'd say it's never hitting closed loop. That's pretty far. No code for that.

Rauch

Lately, it's been running a lot worse. In Neutral/Park, after warming up for a few minutes, the RPM will raise and lower from about 750 to 100RPM and will tend to stall after a few minutes. (Of course it does it during the emission test, which I still ended up drastically failing!) In gear, it'll do the same but not as drastically. With my foot slightly on the brake I'll feel it start pulling me forward for a second followed by a quick cease, and than it'll start pulling and stop.

While driving the other day, I'd get an SES light on for a few seconds and than it will go away. But the way it runs combined with the codes it's throwing doesn't quite add up.

It's throwing:

12 - No Distributor Pulses (Which is normal in ACCY)
13 - Oxygen Sensor (Guess it's not entering closed loop? Haven't installed the heated O2 yet)
15 - Coolant Temperature Sensor Circuit - Low Temp Indicated
34 - MAF Sensor Circuit - GM/Sec Low
44 - Oxygen Sensor Circuit - Lean Exhaust Indicated

Now, I'm not sure when all these occured, but I just pulled them. I left the car in accy mode for a few minutes while I tried to find a paperclip, so I'm not sure if any of those codes occured due to leaving it in accy for a short time.

The MAF sensor was replaced in September by the previous owner. I just replaced the CTS on the intake manifold last week.

Now, the symptoms don't seem to add up. Especially the code 44. A lean exhaust code, yet my car failed emissions by ten fold and it's running richer than anything imaginable. The unburnt gas fumes can be easily smelled behind the car when it's running as well as while stopped at a stop light. As well as the scent lingering for a few moments after turning the vehicle off.

This car is really becoming a pain in the ***, but I'm not giving up yet... Just cannot find out how to fix it and where to start!

hdis2002

iTrader: (1)

If the prev owner replaced the injectors with a higher flow model, that will cause a rich problem if the ecm isn't retuned.

MaxpowerTA

With that combinition of trouble codes and the history of that car (you dont know what the previous owner has done) It will be practically impossible to diagnose and fix this thing without using a scan tool. Running the trouble codes with a paperclip only gives you half the picture at best, you need to see realtime data to find out what is going on. With it you could look at the crosscounts to see if the o2 sensor is working correctly, you could look at the ignition advance to see if it is being corrected by the ecu, and all sorts of other things that will help you to sort it all out. You mention the fans come on as soon as you turn on the key? If that is the case, your car is in limp home mode and the ecu isnt controlling anything that will make it run like crap and deffinately will make it fail emmisions. You NEED to get a scan tool on it.

Rauch

That makes sense. Guess I'm going to have to see the snap-on guy at school and drop some money on an ethos. I've been meaning to get one for a while, and those things make everything easy.

As far as the fans go, that is correct. I haven't traced the wires back from the relay yet to see if they were permanently grounded, assuming it's a ground sided switch. But if that was the case, wouldn't they always be running if it was bypassing the switch?

IF it's in limp home mode, would no sensor readings would show up, or would they just be very far out of wack? I'm guessing that if it is in limp home mode, I'd need to replace the ECU.. But as far as limp home mode goes, why wouldn't an ECU failure code be thrown?