I'm getting close to having the car finally run, but something's still not right. Ater replacing the ECM harness (stand alone Painless), upgrading to new Opti and timing set, and a few other things, I'm running out of ideas.

We've done all of the standard engine checks and it appears that the build up was good - compression is ok, I think the vacuum issues are gone, valves are adjusted (again), etc.

It's a vast improvement over when I started last week, but it's still searching for idle, stalling, and smoking a bit (mostly gray, some black).

I'm looking at eliminating all variables that could be adding up to contribute to this condition. Here are my thoughts:

Spark plug heat range (I currently have cheap-O Champions because it's been fouling them quickly)
Spark plug wires (http://forums.corvetteforum.com/show...post1554559216)
Gas - should I need to run 100 octane with my set up? It's not THAT extreme, is it? The tank is full of 93 pump gas.

What else?

Specs below in sig.

 

How about a link to your last post and what has been done since then.It is hard to remember what you did.

As far as plugs a hotter one will draw heat slower from the cylinder and colder one will actually pull it faster.
Here is a good link
http://www.ngksparkplugs.com/techinf...s/techtips.asp

 

Ditto on the link. I'm guessing you don't need more than 93 octane. Mine has no issues w/ it and I'm currently at 11.3:1 SCR.

 

The sig doesn't say anything about a tune or the compression ratio. Where does the 100 octane notion come from? If you haven't addressed them previously, I would suspect the 30# FMS injectors could have something to do with it.

RACE ON!!!

 

Right -

Tune by Alvin at PCMforless.

Compression is stock, maybe slightly higher due to more airflow. No changes were made to head gasket or bottom end to change it.

What's the theory on the injectors? Too much fuel causing the computer to advance timing to lean things out?

I went to the bigger injectors after the car had a miss when we first turned the key. After discussion here on CF the determination was that the car may not be aggressive enough to "require" bigger injectors, but that they would not hurt. I did have a bad stock injector, so the miss went away, but that doesn't mean the 30's are necessary. I can try some stock ones to see if it leans out. Anyone have any lying around?

The higher octane thought is a result of the detonation (manifested in audible spark knock). I was thinking higher octane may burn more completely and prevent ECM from advancing timing.

 

Not sure that the links would help, I started chasing it as a timing issue, then a computer issue, then a vacuum leak, then replaced the ECM wiring harness (which seemed to do the most good).

Vacuum issue - not fully resolved but getting better. No leaks evident so I think low vacuum casused by other issues. Measured around -12 in/hg yesterday. Posts:

http://forums.corvetteforum.com/show....php?t=1336271
http://forums.corvetteforum.com/show...88&forum_id=48

Timing issue - did everything possible to fix timing, so all mechanicals are good. New Opti ('95 version), new timing gear set, all realigned. Post:

http://forums.corvetteforum.com/show...64&forum_id=48

There are older ones but I think they've been closed.

I think it's turning into a combination of things that are confusing the computer and causing it to try and advance timing and mess with fuel delivery to compensate.

 

Post which lead to changing injectors:

http://forums.corvetteforum.com/show...m_id=48&arch=1

As stated above, swap fixed vibration but not rough condition.

 

Are you sure the vacuum issues are fixed?
Is your TPS and IACV set correctly?

Do you have a cable and scan/datalogging software?

 

Fouled plugs and black smoke are obviously signs that it is running pig rich. Once the plugs start to foul, the car will run like crap (ask me how I know )

If the car isn't going into closed loop (which is something you should verify), the ECM has no feedback from the O2 sensor(s) and really doesn't know that it is running too rich. You can decrease your fuel pressure (what is it set to now?) in order to lean it out a bit in open loop, but it sounds like there will be more to it than that.

I don't know much about programming for a '93, but 30 lb injectors are pretty big. If the tune is not set up for them, you'll have big time fueling problems.

 

We didn't really "fix" anything on the vacuum. I checked everywhere for leaks and there are none, at least not that substantial. I think that the low vacuum is a result, not the cause of the problem.

Define "set correctly." What are some checks? TPS seems fine, throttle response is normal, but that doesn't mean it's OK. IACV could be bad, but wouldn't the car at least idle fine without it?

Datalogging...sore subject. New harness allows communication with diagnostic tools, but still can't get TTS Datamaster to communicate. This one infuriates me becasue there is no reason I can fathom that would prevent communication now. Spent more than 45 min trying yesterday, will continue tomorrow.

 

I know how you know, mine does it I am using cheap plugs now because it fouls them so quickly. Will switch to good ones once I figure this out.

OK, two things -

I'll check closed loop, I can do this now that the shop tool will communicate. Good idea.

Fuel pressure - about where it should be, 47-49 psi. I did not add an AFPR, do I need one?

You're the second to suggest injectors, maybe that's one of the reasons. BTW, I added them after the tune.

 

47-49 psi / stock FPR is fine for right now. I just thought if you did have an adjustable, you could lean it out a bit.

Bingo - If Alvin programmed your chip for the stock injectors (and you now have 30s), there is a LOT of extra fuel being dumped in each time the injector fires, and during open loop, the ECM doesn't know it. Plugs will foul, it'll run like crap, backfire, and will frustrate you to no end. Contact Alvin to confirm, but you will likely need a new chip with the correct injector constant (size) programmed.

Such a pain in the @ss, right?

 

I agree with Byebye You don't mention an afpr in your sig and you will definately need one with those injectors.What did Alvin tune it for the 30# OR stock injectors.Too much fuel will foul the plugs pretty fast and changing the heat range will not help.If you have an Afpr turn it down if not get one I would start at 38psi and go down from there if your tune is not for those injectors and/or get a new tune from Alvin for them.

 

Wow, I'll third/fourth whatever injectors, if you added them, and it's tuned for stock injectors it will run like azz!

 

Injectors vs tune makes sense, but I did talk to Alvin about it before putting them on. He didn't seem to think it would require a re-tune.

I'll contact him and see what he thinks.

Suggestions for a good AFPR? Seems like a good idea regardless of whether or not it's contributing to this particular issue.

Why do you suggest lowering FP, to compensate for the injectors? In other words, if I get the tune adjusted, do I still want to lower the FP?

 

Did you get a piggyback chip from Alvin? IF YOU DID MAKE DAMN SURE YOU PUT IT IN THE ECM RIGHT. Pull it out and check it out.

 

It would compensate it, but there might be a point where you couldn't comp. enough (based on partially what you are saying and the combination you have). FP would also effect it globally. Mine can only permit it do go down to approx. 39# at the rail w/vac. off. It sounds as though a chat w/ Alvin would do some good as well as asking where the FP should be set at based on the tune.

 

I had suggested lowering the fuel pressure to somewhat compensate for the large injectors. Given the same injector pulse width, a lower pressure would result in less fuel being injected. It's one of the ways to fine tune fuel delivery during open loop, but there is only so much you can do. Too low and the fuel will not spray properly from the injector. If it is the tune that winds up needing the adjustment, and you get it adjusted, you may not need to lower the fuel pressure at all.

As I am finding out with my car, a wide band A/F meter is KEY (along with data logging) in helping to dial in the best possible tune.

Re: AFPRs - Summit Racing would probably have something decent at a good price.

 

Yeah it is possible to put em in backwards.

ask me how I know?

 

I thought the FP was supposed to be 41-47, does sound like your on the high side. And you're the first member I've heard going to 30#
injectors , I think I've read where some members had to adjust
just going to Fords Suv 24#.