Getting stumped on stumble, missfire?

S

SMV6LOL

Member
Joined
Aug 3, 2012
Hey guys so ive been fixing problems since I bought the car, first was cooling issue, now its a stumble or missfire?

When I bought the car it had a really tough time idling, would stall at stop lights or when I would release throttle. At WOT it would stumble or missfire. Scanmaster was telling me a few things, MAF wasnt working smoothly, IAC and TPS needed adjusting. Figured id hit everything at once....

Here is what I did this weekend....
Racetronix 460LPH with 8an Feed and 6an return, PTFE of course
Hotwire, also grounded the battery to frame
New stock MAF (yes im going with LS1 but this is temporary, im building a custom intake)
New E3 Plugs ( gap seems high on these but seems like alot of happy E85 guys like them)
New Coil and ignition module
02 Sensor
TT 5.7 E85 chip.

Here is what it fixed:
I can start the car without throttling the pedal
Idle is smooth
Can give it gas in park and RPMs are very smooth(unlike the choppieness before)
Runs like a rapped ape when it doesnt stumble
My AF on scanmaster will hit 255 before it was 230

Here is what im still dealing with:
WOT it will stumble, missfire, buck.... it will happen once or twice during the WOT run. It feels like 100% power then boom 0% in .5 seconds. No codes but will light up check engine light for that second.
-Knock only seems to happen when it shifts?(6 is the highest, for a brief second)
-02 reading are high 780-850
-Out side of that problem she runs freaking awesome..... but this is a problem to me and i dont want to move further until corrected.

Some things to point out:
-When installing the new chip, I couldnt find the orange ecm wire near the battery to disconnect. So i just unplugged both ecm connectors at the ecm and took the cables of the battery. This should have reset the ECM correct?
- I tried adjusting a few things on my chip through the scanmaster and it doesnt seem to stay, basicly when I enter, for example WOT Fuel all gears, the BLM stays at 128 even though i changed it to 137.
-15lbs of boost now hasnt changed since ive owned the car, dont want to up it til i figure the problem out.


Thanks for reading my novel and thanks for the help in advance.
 
Nobody... I cant find the orange ecm wire anywhere by the battery and pictures or better guidance?
 
Trace the orange wire off the positive battery cable. It comes right off the battery pos lead. Also make sure connections are clean and tight. Run your fingers down the positive cable make sure it's not touching the exhaust header.

Rick
 
There are only two cables coming off of my battery (positive side) both are 0-2 gauge. Dont see a little one
 
I had almost same thing turned out to be bad ECM . It would only do it at wot and not all the time. Keep throwing parts at it and Finley browed my buddy's ECM and and ran better than it ever had.

Shaun
 
I have seen some orange wires hooked to the starter. The connector would then be around the air box area.

Trace that positive cable down to the starter. Make sure the cable insulation is not melted and shorted to the header. It's common problem that will cause the ce light to come on and stumble at wot.
 
Yes stainless steel filter, ECM is about the only computer/ignition part i haven't changed.

Im gonna look for that wire, but the ecm can be reseted without unplugging that right? Unhooking thr battery and unplugging the connection to the ecm?
 
A couple of random thoughts...

1. Regarding the ECM orange wire - mine passes under the coolant overflow bottle on its way to the battery. It might help you to remove the coolant overflow bottle screws (two of them) and lift it up.

2. The most important thing you said is that the CEL comes one when your car stumbles. That tells me for sure that this is an electrical problem of some sort - not fuel filter or anything else mechanical. Some things I would check:
a. Are both the battery cables on the battery good and tight? I've been personally burned by this one...
b. Check both the positive and negative battery cables. Are either touching something they shouldn't? Especially the positive battery cable - very common for those to touch the passenger side header under acceleration.
c. Check the positive batter cable connection at the starter - good and tight? How about the negative battery cable connection at the turbo "J" bracket - good and tight?
d. Double-check the connections to the ECU - any bent pins, corroded connectors, etc.?
e. Check the grounds on the back of the passenger side head. Are they all tightly connected to the head? Any of the wires break-off at the ring terminal?
f. Possibly a bad ECU - can you swap it with a known good one?
g. A bit of a long shot - you could be experiencing MAF drop-out. I ran into this problem when my car started to run 11's with the stock MAF. I have several DirectScan file logs of it, so I know it's a real event. Basically, if the MAF sends a signal to the ECU that is low enough frequency (which could happen under very high air flow, well over 255 g/s), the ECU experiences a hardware-related overflow, and the ECU resets itself. When it would happen in my car, the DirectScan file would show the air flow going to near-zero, fuel injector PW going to near zero, etc., but for only one frame (about 1/18th of a second). In the next frame, the ECU would be running fine. This would happen maybe 3 or 4 times in a 1/4-mile run. Each time it happens, I would feel a stumble and get a pop out the exhaust. This is a hardware problem between the MAF and ECU - it cannot be fixed with a chip change. When I upgraded to a Translator+ and 3-inch LT1 MAF, I never had the problem again. Do a search for "MAF dropout", and you should find some more information on it. This would only happen at WOT, so if your stumbling also occurs at part throttle, it's definitely not MAF drop-out. Honestly, this is probably a longshot, but if you exhaust all other options, maybe consider this.

Good Luck,
 
That maf drop out sounds like it could be it. Basically i lose power for a split second. Makes sense if the ecm is resetting itself? Im going to take a good hard look at all my positive and ground connections then if nothing look into a upgraded maf
 
i dont run e85,but from what your saying it sounds too loaded up with fuel for 15psi of boost,you could try bringing the gap down on the plugs, i gap real tight on all my motors but again i dont use e85..if your going to get the bigger maf and translator you could give that a shot but the stock maf went into the 10's on my car with no issues.i would contact eric and see what he thinks.a wideband o2 and pulling plugs can really help you dial the car in
 
SMV6LOL said:
Hey guys so ive been fixing problems since I bought the car, first was cooling issue, now its a stumble or missfire?

When I bought the car it had a really tough time idling, would stall at stop lights or when I would release throttle. At WOT it would stumble or missfire. Scanmaster was telling me a few things, MAF wasnt working smoothly, IAC and TPS needed adjusting. Figured id hit everything at once....

Here is what I did this weekend....
Racetronix 460LPH with 8an Feed and 6an return, PTFE of course
Hotwire, also grounded the battery to frame
New stock MAF (yes im going with LS1 but this is temporary, im building a custom intake)
New E3 Plugs ( gap seems high on these but seems like alot of happy E85 guys like them)
New Coil and ignition module
02 Sensor
TT 5.7 E85 chip.

Here is what it fixed:
I can start the car without throttling the pedal
Idle is smooth
Can give it gas in park and RPMs are very smooth(unlike the choppieness before)
Runs like a rapped ape when it doesnt stumble
My AF on scanmaster will hit 255 before it was 230

Here is what im still dealing with:
WOT it will stumble, missfire, buck.... it will happen once or twice during the WOT run. It feels like 100% power then boom 0% in .5 seconds. No codes but will light up check engine light for that second.
-Knock only seems to happen when it shifts?(6 is the highest, for a brief second)
-02 reading are high 780-850
-Out side of that problem she runs freaking awesome..... but this is a problem to me and i dont want to move further until corrected.

Some things to point out:
-When installing the new chip, I couldnt find the orange ecm wire near the battery to disconnect. So i just unplugged both ecm connectors at the ecm and took the cables of the battery. This should have reset the ECM correct?
- I tried adjusting a few things on my chip through the scanmaster and it doesnt seem to stay, basicly when I enter, for example WOT Fuel all gears, the BLM stays at 128 even though i changed it to 137.
-15lbs of boost now hasnt changed since ive owned the car, dont want to up it til i figure the problem out.

Thanks for reading my novel and thanks for the help in advance.
Click to expand...

Sent you a pm

Sent from my iPhone using Turbo Buick
 
Have u noticed if it does it if u hit a bump in the road or turning left or right?
 
Bad spark plugs, fuel filter, and too much fuel have all been mentioned. I don't believe any of those would cause the CEL to go on for a second and then go off. They could all make the car run poorly, but not turn the CEL light on for a split second.

Most people with stock MAFs that I've known don't have a problem with MAF drop out. I was one of the unlucky who did. It's a long shot that your problem is being caused by this, but possible, something to be aware of. I would check the previously mentioned electrical stuff first.

Sent from my SCH-I535 using Turbo Buick
 
Check the orange ecm feed wire real close...common for the wire to be broke internally by the black little block. I had mine doing a very similar thing and the wire had broke internally and looked fine on the outside but the strands inside were all broken right next to the block. Had same issue on 2 other turbo regals
 
Well ive got to find that the orange ECM wire first to inspect it..... this is why i hate buying previous owners car, who dont know how to work on cars

I agree with Mike because ( as I probably labeled this thread wrong) its not a sputter its a complete lose of power for a split second... which tells me its not a misfire its something in the computer wigging out. Like the MAF dropout.
 
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