Stumble/Backfire at WOT

[mtbraun]

So I'm out with the car after a month or so break, and after an hour of highway and light cruising decide to mash it from a slow (5mph) roll. The car stumbled, backfired a couple times, then took off, backfired a couple times, then took off again. Alarmed I checked for KR - nothing. All scanmaster numbers look decent besides a slight lean condition at idle (BLM 142) I've been battling for awhile. Nothing has changed in my setup since last cruise or since I was last working on the BLM issue.

Took it out a few days later and did the same thing. No stumble when going WOT from a fast roll.

I think the gas is in good shape as I'm currently mixing 50-50 110 with 91 pump. Using Delco 43s gapped at .032. New plug wires.

Could this be the coil?

If so, and I go with the Highway Stars coil, any reason to go with the high output coil they offer?

 

[mtbraun]

Anyone?

 

[Nick Micale]

The dealer-method to troubleshoot issues like yours was to visit the parts room and change items until the problen was solved. Worked well under warranty, but not so much now unless you have a spare parts room?

Your issue sounds like an electrical item, but which one?

With a scan tool you could check some values of components.

A MAF reading would be erratic as would the RPM if the crank sensor is faulty. Coil/module can be checked if you have the Casper's coil tester, or just swap a known good one. A bad wire you can find with an ohm meter.

Too bad you are not closer Matt, but this is the best I can do for now, sorry.

 

[TurboBuRick]

What cam sensor? Stock or something else? Same question on crank sensor?

 

[mtbraun]

What cam sensor? Stock or something else? Same question on crank sensor?

Stock crank sensor. Caspers cam sensor cap, rest is stock.

If it were one of these two items, I'd like to understand why it would cut out at this point and not at others. I get that stuff fails now and then but why in only a small portion of the rpm range?

 

[mtbraun]

The dealer-method to troubleshoot issues like yours was to visit the parts room and change items until the problen was solved. Worked well under warranty, but not so much now unless you have a spare parts room?

Your issue sounds like an electrical item, but which one?

With a scan tool you could check some values of components.

A MAF reading would be erratic as would the RPM if the crank sensor is faulty. Coil/module can be checked if you have the Casper's coil tester, or just swap a known good one. A bad wire you can find with an ohm meter.

Too bad you are not closer Matt, but this is the best I can do for now, sorry.

I'll check AF. RPMS are smooth and steady...of course except for when it cuts out. Don't have a coil tester but is there an alternative way of doing this?

 

[TurboBuRick]

Bingo!

Throw the caspers cap in the garbage and put the stock one back on. Problem solved.

Rick

 

[84BuickGNYorkPA]

Any update?

Chuck

 

[mtbraun]

Nothing yet. Hoping to get out tomorrow after a couple changes. Will post soon.

 

[mtbraun]

Bingo!

Throw the caspers cap in the garbage and put the stock one back on. Problem solved.

Rick

Thanks for the suggestion. I will try that. Can you explain why this would possibly cause the stumble?

 

[TurboDave]

Bingo!

Throw the caspers cap in the garbage and put the stock one back on. Problem solved.

Rick

Why is that?? Mine's been going strong for several years.

 

[TurboBuRick]

I can't tell you how many cars I've fixed by removing the caspers cam sensor cap. I don't know what the problem is but know what fixes it. Stock ones go bad too and start to cause the same condition but the l.e.d. caps have a much worse track record IMO.


RL

 

[mtbraun]

When pulling the coil to change injectors I noticed this on the coil harness plug. It might be hard to tell from the pics but there are two plug recepticles that are pushed back into the plug. Perhaps this might be part of the problem...either way it should be corrected. Is there a way to extract the receptacles so they are flush with the end of the harness plug? Is there a way to get them to stay put in the harness plug so when reattaching they don't just push back into the plug?

 

[trbojo]

i'm looking at the 3rd from the right and how spread it is....you can slide them all the way out, use a small pick to tighten up the spread ones and pull the retaining tang out that holds them in the connector body....looks like you may have found your problem....

 

[mtbraun]

That worked - thanks much.

 

[trbojo]

That worked - thanks much.

np...glad you found it fairly easy...