1990 Trofeo - 3.8L

Hi guys,

I was listening to the sweet exhaust sounds coming from the Trofeo today when I noticed that it seemed to be backfiring a lot. The car accelerates smoothly, but on some rare occasions there seems to be a miss or hesitation while accelerating slowly. Also if i jam on the accelerator while in park there seems to be a slight hesitation before it revs. Also as stated in another post, I am getting ECM codes - throttle position sensor (voltage too low) and cam sensor circuit. I don't know if these things are connected in any way, but hopefully someone knows.

Thanks,

Barry

We can't really tell if you're overreacting or not unless you can get a sound clip of the exhaust and post it.....

TOC Admin
Brando

Ok Brando, here's the clip:

"Glug, glug, glug, glug, pop, glug, glug, pop, glug, pop, pop, glug, pop!"

Is the "pop" really loud? Does the engine idle drop when it pops?

TOC Admin
Brando

Since when did u get the TPS voltage to low code? maybe ur tps is bad or needs readjusting measure the voltages i believe it should be around 0.4 volts at idle and at WOT it should read 4.25 volts minimum. voltages higher than 4.25volts indicate WOT to the ecu i believe.

you dont have to turn on the car to read this, u can do it with the ignition in the on position.

If your TPS is giving codes, your computer is in open loop mode! You cant expect the machine to run properly when it's crying for mommy!!! Eliminate those codes and you might find a difference.

Also, take your plugs out and look at their color. How are your wires? I've had enough problems with wires and the like to not mention it in misfiring cases

Hey guys,
I apparently have a little backfire on my delta 88 too.
When I was cleaning the snow off the car today...
I got in the car after I was done (it was warmed up) and I pressed the gas down to listen to it.

When it idles, it goes: glug, glug, glug, glug, glug, glug
It sounds fine...although on warmer days, the thing idles really bad...still haven't figured out that rough idle problem on it.

Now, when I step on the gas and then let go: *press gas* glugglugglugglugglugglug *let go* glug glug glug pop pop *idle* glug, glug, glug

The pops aren't too loud...but it definately doesn't sound normal. It doesn't pop at all during acceleration...none that I can hear anyways.

Any ideas? I have a PCMCIA Serial card on the way, because I think that Serial to USB converter was messing up my ALDL readings.

TOC Admin
Brando

ops:

brando... Just get used to the rough idle thing... I havent seen a way around it. Mine has always idled rougly, and I am not sure that anything can be done.

Swap for a 3800 series 2

NOT THE ANSWER I WAS LOOKING FOR!!!!!



TOC Admin
Brando

the explaination I was given was that GM added a "balance shaft" starting with the 3800 series 1. Our engine is the old lazy 3.8L. I've talked with many people who have the same idle problem as we do.



I forgot exactly what the balance shaft was connected to, or what exactly it balanced, but aparently it works! Maybe someone else here can explain what that balance shaft did.

Hi all,

The V6 is, by nature, unbalanced and it took untold Millions of dollars in research to make it work as well as it does. All to save a little underhood space.


The concept is to attach another out of balance shaft to it and turn it the opposite direction. Theoretically, the interaction of the harmonics will make it run smooth.

Regards, Norm

this is why most newer V6's are of the 60* v6 design as it doesnt require split rod journals on the crank and no more semi even fire spark pattern (Norm you remember the old 3.8/4.1L buick v6's with the odd fire (common rod journals)-man did those things shake!)

the seriesI/II 3800's have the balance shaft in the lifter valley and is driven by a gear on the back of the cam timing chain gear even the 4.3L v6 has a balance shaft.
anyway good luck brando
have you sprayed the wires etc with soappy water and looked for voltage leakage? some ignition cables can induce a spark in an adjacent wire if they are routed too close together/touching.
the other possibility is if it's worse with a cold engine one of the injectors might not be misting the fuel but spraying a stream which doesnt vaporize fast enough and cause something very similar to a missfire (technicly a lean missfire as the mixture isnt evenly distributed) most of the time a good fuel system cleaner will help but sometimes you acually have to have them taken out and cleaned/reverse flowed to clean em properly.

to check this you can disable the spark (make sure you do!-unplug the coils!) and pull the inj rail and injectors and watch the spray pattern with the engine cranking.

the other thing you can do to see what cylinder is contributing the least is to take the coil wires off (on DIS this works great) and put a short piece of rubber vacum line over the coil terminal and place the wires over these, then use a test light or ground wire with the engine running to "cancel" (ground) each cylinders spark and see which one gets rid of the missfire/poping.
hope this can help ya some more!
good luck brando! James

Wow, lots of good things to try out there.
First off, soapy water to test voltage leaks? Never heard of that one before...gas pipe leaks, but voltage?

I'll have to try the pulling the injector rail and see what it does (making sure to disconnect the ICM ). So it should just be a nice misting?

Thanks,
TOC Admin
Brando