Misfire/surge under load - need opinions - Long Help

[QKRNYRS]

Ok, you know how it is, whenever you are working on your own stuff,. nothing seems to go right. Well, that is sooooo true here.

My GN with a Speed-Pro 72 lb injectors, champion heads, houston headers, 3.5" DP etc... etc... has a problem.

It misses and pops through the exhaust on full throttle acceleration. It seems to have gotten alot worse lately. Here is the history..... It seemed to have a slight miss/surge at the top end 5500 RPM+ ........ I then had a cam sensor failure that caused some MAJOR backfires.... after fixing that, I decided to test my coil/module with the Caspers tester. I had a breakup at higher rpm, I swapped the coil wires around at the module and dertermined that it was a module failure. At this point I decided to go and switch to the Type II ignition.

Well, things after this are just down hill. With NEW GM module, MSD coils, new plug wires, plugs, just for a tune-up and the new cam sensor, it misses and pops through the exhaust worse than ever.

So, ok, possibly an intermittant crank sensor? Put a new one on. No change. Checked fuel pressure, seems to hold under acceleration. Dropped timing back, no change. Excessivly richened up the map, no change. Leaned it out, no change. Then I talked to Lonnie Diers about the situation. He said to try Valvesprings, sounded like valvefloat. New tool-steel valve springs, possibly better, now seems like a surge but then the more I drive the car the worse it gets. I''s not the same everytime I get on it. Sometimes it's a clean 1st gear and then sputters slightly in 2nd. Sometimes it's just a miss or two followed by a sputter.... and depending on how pissed I am will depend on how long I stay in it.


Questions:

Injectors? Possobly faulty under a load?

Speed Pro ECM has anyone ever experianced a failure?

Fuel problem that doesn't show up on a gauge? I have a Walbro 340m with a bosch external. What about cavitation?

I'm searching for any help.

Thanks!!

Pat

 

[bobc455]

Pat-

What is your timing, VE, RPM, MAP, actual A/F & target A/F when this happens?

Have you played with things like AE vs. MAP?

-Bob Cunningham

 

[QKRNYRS]

Bob,

I can send you a log file if you want to look at it... I haven't tried AE vs. Map though. Just the base map.

Pat

 

[1985BuickGN]

Pat, you would'nt happen to be from Mishawaka/South Bend area? Anyway, I know a guy (Chris) who had almost the same problem with almost the same set-up as yours. He never figured it out, I don't think, but I know it was a timing issue. I think the more timing he ran, the better it got. Hope that helps. Paul.

 

[Chuck Leeper]

Surge?

You said:
"Fuel problem that doesn't show up on a gauge? I have a Walbro 340m with a bosch external. What about cavitation? "

Does the fuel press remain steady under boost? IF so, what is the baseline and what does the FP gauge read at WFO??
Depending on the output of the fuel pumps, you can have a problem in that one pump will out produce the other.
IE:
A. The 340 is weaker than the Bosch, thus the Bosch is put in a "lack of supply" situation, and goes to cavitating.
B. The Walbro is doing a better job than the Bosch, and the Bosch becomes a restriction.
Without knowing more about the combo, and your goals, it's hard to tell if you even need both. The 340/72# inj's should take you to hi 10's.
I doubt an injector would be the culprit. I flow and clean allot of them, and rarely see that.
Bad grounds can be a problem, low voltage can, bad plugs or excessive gap on them, YAdda, yadda.
What does the data log tell you about the O2 correction when this happens?
Do you see any volts drop on the logs??

I'd send Bob your logs and athe GCT file and he can see if he can find a problem...

 

[Reggie West]

Try these 2 little tricks.

Change the plug gap to .025 you probably have them set at .035.
You did not say which turbo you have but for 72 lb/hr injectors you are probably running a 70 or something close. It is possible to blow out the spark in the cylinder with bigger turbos. We did that on a dyno once and picked up 60 HP.

EDIT: Just saw your sig PT 70.


It sounds like you have a ground problem ( typical Buick) , you can run a ground wire from the back of coil pack to the firewall and see if that helps.

If it is still doing it, I might suggest a MSD box.

Chuck can tell you all about missing at higher rpms.

 

[Craig Smith]

I miss a lot when I'm loaded too.

I agree with the notion that this is an ignition problem. If closing the plug gap helps, you are blowing the spark out and you can work at it from there.

 

[ULUZ2A6]

I am replying on Pat's behalf, as his ISP is down.

We put new plugs in this weekend gapped them to .028 and made two "runs" through second gear, popping and all. We then took it directly to the garage and puled the plugs. All looked okay except for # 2. It looked lean, almost white. We then ohmed the injectors and all were at 2.7 or 2.8. We then tested each injector
with an OTC tester. Pulsed each for 50 times at 10ms each. Fuel pressure dropped from 45 psi to 13 psi on each injector. We also checked the resistance and terminal tightness of the injector harness and had .40 ohm's resisitance on each wire which lead us to believe that it is good.

When we gapped plugs closer we went noticed the miss changed from a hard hard misfire to a more of surge or a light mis fire.

This happens at 15 psi of boost.

Could this be injector spray pattern?

Could this be an internal injector driver?



Chuck, yes we know Chris. In fact just sold him some wheels. Chris has a stock ECU, Pat has a FAST.

Thanks for all replies and help. Keep them coming.

 

[Craig Smith]

If tightening the plug gap helped the problem, the ignition is weak. I don't know of another problem that closing the gaps would help. I think you have found it.

 

[Craig Smith]

P.S. ULUZ2A6, I remember seeing a TB with that plate on it at the 1995 US nationals as we were leaving Sunday night. That sticks in my head cuz we got to stare at it all night in the traffic jam. Would that have been you?

 

[1985BuickGN]

ULUZ2A6, that was not Chuck, that was me 1985BuickGN, and the Chris I'm referring to has a light blue 86 or 87 Camaro, with an 87 GN engine, with a FAST system, not stock, believe me, I know alot about this car. Probably a different Chris.

 

[Russ Merritt]

Are they MSD super conductor wires? I had all kinds of problems running those.

 

[QKRNYRS]

I'm back...

Well, like Chip (ULUZ2A6) said, though the plugs were mostly dark after just a couple of short bursts really. Except #2. Which was white..... While I have to agree with Craid that by closing the gap the miss did get better and would seem to be ignition.. A lean mixture is also harder to light off than a rich mixture. So, in theory, by closing the gap I could be just "lighting it off" and making some power out of that cyl.

The one thing that I didn't mention that I forgot to have Chip post, is thtat EGT's are OFF THE MAP!! I mean like on a 1st and 2nd gear pull with the miss occuring, 1900°. No lie.. What does that indicate? Real lean? Or could an overly rich mixture (or a misfire) be burning fuel in the exhaust?

So what gives? Yes, they are MSD super conductor's. I did assemble them myself, but used the MSD Crimpers. I am gonna try the ground from the coil bracket to the ground block next, and anymore suggestions are GReatly appreciated Thanks!!

Pat

 

[Chuck Leeper]

1900!!

Holy CRAP!! 1900*??
What is the O2 correction saying??? If that's the case, you have some kind of a fuel shortage...

Do you have any data logs?? Can I see them?? I run the fast on my car, and can maybe see an idea or two... send me the GCT that matches to 1900* egt and the logs

codymotorsports@usa.net.