3500 problems

[asylummotorsports]

I'm having an issue with my car in that it will run just fine at WOT (14.19 thru the exhaust) but in the shut down area the tach jumps up and down like hell and it's missing and stalling.

Takes several attempts to go from Neutral to Drive without stalling.

And while cruising home it's fine under load, but back off even a little and the missing and backfires start again. Put it neutral, rev it, and it will clear and I can put it back in gear and continue driving.

NO CODES!

Pulled the UIM, injectors test good with the meter.

Oil pressure good as ever.

Looking for ideas!

Thanx

[Joseph Upson]

Possibly your ignition module, jumpy tach and misfiring.

[Superdave]

has it always done this?

i agree.. could be the ICM or a bad engine ground. Check out the IAC motor too...

[asylummotorsports]

No this is new Dave.

Rodney was down today and hooked up his laptop/Tuner Pro and eliminated the IAC/TPS possibility.

They are perfect.

Vaccuum is 20# and consistent. (Is that ok??)

The MAP seems to be an issue or perhaps the FPR.

Pulled the vaccuum from the FPR and nothing changed! ???

And the MAP has some connection issues.

I also pulled the plugs. WHAT A FUCKING MESS! Chris, I will shoot you!

OK my bad for not looking before this but it was running fine.

Delco 3100 regulars gapped between 25 and 40 and Venture Van heat range!

New Delco Irridiums I have had for a year are now in.

It also FINALLY threw a code. O2 sensor. (With the headers it was only reading one bank.)

Rodney disconnected that and hard-wired my wideband that is downstream in the collector into the ECU and that helped it alot.

So I'm buying a new MAP tomorrow and putting a gauge on the fuel pressure.

From there we will see.

[robertisaar]

if you pull the FPR and nothing changed then i'd say its bad.... it should go noticeably rich, like in the area of 5-10% minimum...

[SappySE107]

not really that much. Easier to check the pressure itself and put a vacuum tester on the FPR.

[3400-95-Modified]

Delco 3100 regulars gapped between 25 and 40 and Venture Van heat range!

I don't see whats wrong with running those plugs...

Granted the 25-40 gap range doesn't help, but whats wrong with a Venture heat range? 41-101 vs the 41-105? I don't see the huge issue... I'm going to TR6's to support my nitrous next year.

[IsaacHayes]

Any 3x00 plug should run fine as long as it's in spec.

[AaronGTR]

What ECU are you using that allowed you to use a wideband signal?

[robertisaar]

there are wideband to narrowband translators out there...

i know TGP code and probably 8D as well have been refined to use a WB for main fueling as well...

[asylummotorsports]

The plugs I took out are R44LTSM and are a mess. The porceline an 5 of them is loose and there is ample evidence of leakage.

There is only about 4000 MILES on this swap, so those plugs were NOT new, IMHO!

A testiment, I suppose, to just how good the GM ignition system is that the car ran as well as it did.

New 3500 Delco Irridiums are in. (Just watch! The damn thing will run slower!)

As far as the O2 and that stuff goes, it threw an O2 sensor code and Rodney just disconnected it and hard wired the PLX wide band into the ECU.

Seems ALOT happier. And does explain the symptoms.

Ran great at WOT (O2 is ignored) and ran like crap everytime I backed off at all.

I'm taking it for a good ride tomorrow before I commit to this weekend at St Thomas.

Thanx everyone!!

[asylummotorsports]

What ECU are you using that allowed you to use a wideband signal?

It's the stock '92 ECU that Rodney has been messing with for about two years or more.

To be honest, this is all beyond me, and I really can't answer your question intelligently, but I'm sure someone will pipe up.

[3400beretta]

The wideband has a narrowband output.

And Eric, the more I think about it, the car may have benefited from running a colder plug, so it infact may be slower!

[asylummotorsports]

And Eric, the more I think about it, the car may have benefited from running a colder plug, so it infact may be slower!

PERFECT!! It just gets better doesn't it?

LOL!

[pocket-rocket]

You need to read your title to your car. BTW, I like that title, lol. I wish more people on here followed it. I liked St. Thomas. We had our 60v6 meet there years ago. Nice country, nice people (Franz and his family rock), big junkyards. I enjoyed it there.