Author Topic: Question about a 3.8L  (Read 722 times)

DeCaff2007

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Question about a 3.8L
« on: September 15, 2018, 08:05:30 PM »
Gents, I've been chasing a no spark issue on my 96 Firebird for a long time now, and finally found the issue the other night.  It turns out that the 14-pin connector to the ignition control module was bad.  A friggin hairline crack was causing an intermittent connection, hence no spark.

Ok so I ordered another connector from rock auto (to the tune of $77   :shock: :shock:!@$#%).  I soldered it on, wire for wire and double and triple checked my work.  I even performed continuity tests on each wire.  There's NOTHING wrong with my soldering job, the wiring, nor the connector, yet......

.... when I started the car to do a test drive, it was hard to start, stumbled, then revved to 6K rpm and stayed there!  WTF???

Guys, I've been through every bit of wiring that I can see under the hood.  What in the HELL would make an engine rev that high, just sitting there?

If anyone has any suggestions, I'm open to them. 

On another note, scroll to Figure 8 in the following link:

https://www.autozone.com/repairguides/GM-Lumina-Silhouette-Transport-APVs-1990-1999-Repair-Guide/Electronic-Engine-Controls/Crankshaft-Position-Sensor/_/P-0900c152801dba4b

I have noted that pins L, M, and P of the ICM all have continuity together.  Seems to me that shouldn't be but what do I know...



1976 T/A 400, 4-speed swap.... 

Check out my resto thread:  http://transamcountry.com/community/index.php?topic=48626.0

It's all trial and error until something lines up...

hakitup

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Re: Question about a 3.8L
« Reply #1 on: September 16, 2018, 09:58:50 AM »
Throttle position sensor or maybe the idle air bypass might be something to look at.

Tom H
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firebirdparts

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Re: Question about a 3.8L
« Reply #2 on: September 16, 2018, 01:06:06 PM »
It takes air for the engine to run, so the throttle is open, or you've got a big hole open somewhere, like a PCV return hole or something like that.

An engine can't run 6000 rpm just due to sensors or any kind of computer mistake, unless the computer can control the throttle directly.  It needs air and fuel to run that fast.
I want to be like Paul Kenny when I grow up
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1977 Y82 4-speed (red interior)
1978 Skybird 350
1978 Redbird 305
1979 Redbird 301 4-speed
1992 Lincoln Mark VII LSC/SE (red)
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1953 Chevy pickup (converted 4x4)
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hakitup

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Re: Question about a 3.8L
« Reply #3 on: September 16, 2018, 05:24:08 PM »
Yeah, I guess it would flood if those sensors were reading wrong and no extra air was given.

Tom H
"I don't know what you call it, I only know the sound it makes when it lies!!"

DeCaff2007

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Re: Question about a 3.8L
« Reply #4 on: September 16, 2018, 06:42:22 PM »
It takes air for the engine to run, so the throttle is open, or you've got a big hole open somewhere, like a PCV return hole or something like that.

An engine can't run 6000 rpm just due to sensors or any kind of computer mistake, unless the computer can control the throttle directly.  It needs air and fuel to run that fast.

^^This.  My first though was where is the engine getting enough air to do this?

I had seriously thought that the throttle was stuck open somehow.  It moves back and forth freely (as in not stuck open lol), though, so how the HELL is the engine getting enough air to rev to WOT?

The computer has no direct control over the throttle.  I only have a TPS, IAC, and MAF.  I had unplugged each one individually and tested the RPMs.  The only one that made a difference was the MAF sensor. 

Upon unplugging, it was difficult to start, then idled almost perfectly for about 3 seconds before acting like WOT again.  Then, however, it idled perfectly, WOT, idle, WOT... you get the picture.

Also, the MAF is cracked and I can see the leads inside the plastic housing.  I'll find another and replace it, but I don't think that's the issue.

As for a big hole somewhere... I'm at a loss. 

Again, all I did was solder on a new ICM harness connector.  Nothing has been the same since.

I did not, however, disconnect the battery while doing that.  Is it possible I've fried the PCM somehow?

Keep the replies coming.  They do help!
1976 T/A 400, 4-speed swap.... 

Check out my resto thread:  http://transamcountry.com/community/index.php?topic=48626.0

It's all trial and error until something lines up...

Re: Question about a 3.8L
« Reply #4 on: September 16, 2018, 06:42:22 PM »

DeCaff2007

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Re: Question about a 3.8L
« Reply #5 on: September 18, 2018, 10:51:57 AM »
Ok, not to double post and bump my own thread, but I have a small update on this.

I taped a piece of cardboard over the throttle body.  Turned the key and would not start, period.  Ok, it's starved for air.

So I gave it half cardboard, lol.  It BARELY started and guess what....  the idle went to 3500 - 4000 RPMs.  Hey, better than the 6K+ it was at.

I tore the throttle body off at this point.  Aside from a lot of carbon buildup, there was nothing out of the ordinary - but the throttle body gasket came off in 17 pieces.  The darn thing is special order.  Grrrr.

I need a new MAF sensor, anyway, so I'm about to head off the junkyard.  The throttle body is proprietary to 96 - 98 F-bodies, but the MAF sensor fits many, many vehicles.

Otherwise, the woman and I are out of here for a few days.  I'll post back once we return and I get a chance to actually put this thing back together.
1976 T/A 400, 4-speed swap.... 

Check out my resto thread:  http://transamcountry.com/community/index.php?topic=48626.0

It's all trial and error until something lines up...

FormTA

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Re: Question about a 3.8L
« Reply #6 on: September 18, 2018, 11:30:17 AM »
I think you are on to something. Good luck!
79 Trans am 301 (work in progress) LS swap n progress
79 Formula 301 (Work in progress)
67 RS Camaro (Work in progress)
See the recurring theme???

DeCaff2007

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Re: Question about a 3.8L
« Reply #7 on: September 18, 2018, 09:16:04 PM »
I think you are on to something. Good luck!

Sure, great, but what would have caused this problem?  All I did was replace one darn connector.

Gah....  I have many other things to focus on right now than this.

1976 T/A 400, 4-speed swap.... 

Check out my resto thread:  http://transamcountry.com/community/index.php?topic=48626.0

It's all trial and error until something lines up...

FormTA

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Re: Question about a 3.8L
« Reply #8 on: September 19, 2018, 04:57:07 AM »
This may sound dumb but could you possibly have leaned on it causing it to move enough to loosen the casket and create an air leak?
79 Trans am 301 (work in progress) LS swap n progress
79 Formula 301 (Work in progress)
67 RS Camaro (Work in progress)
See the recurring theme???

DeCaff2007

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Re: Question about a 3.8L
« Reply #9 on: September 19, 2018, 05:38:20 AM »
This may sound dumb but could you possibly have leaned on it causing it to move enough to loosen the casket and create an air leak?

Casket?  LOL!!

Anything is possible at this point, I guess.

Maybe this poor thing is trying to tell me to swap a V8 in there......
1976 T/A 400, 4-speed swap.... 

Check out my resto thread:  http://transamcountry.com/community/index.php?topic=48626.0

It's all trial and error until something lines up...

DeCaff2007

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Re: Question about a 3.8L
« Reply #10 on: September 20, 2018, 05:37:30 AM »
Gents,

I've found the problem!  I would have never guessed it if I didn't have the foggiest idea where to look, either.

So, I took the throttle off with the intent of checking the throttle plate, gasket, and cleaning the crap out of it.

I did all that, and all was well, but then when I was putting the throttle back on (yes, even without a gasket), I noticed the bracket that holds both the throttle and cruise control cables was giving me a fight going on.  It was almost like the cables were jamming somehow.

Sure enough, the cruise control cable was damaged right around the spot where the ICM is.  That's also the last place I was working.  It was damaged such that it was making the cable a half in shorter at the throttle, thereby pulling it open. 

So, I simply left that cable off until I can get a new one (IF I get a new one).  I put the rest of the intake back together and fired it up. 

Now the idle is right around 1K.  Still a bit high, but that's probably due to the lack of a throttle body gasket.

Now, the woman and I can go on vay-cay and this won't be on my mind :-)
1976 T/A 400, 4-speed swap.... 

Check out my resto thread:  http://transamcountry.com/community/index.php?topic=48626.0

It's all trial and error until something lines up...

79GoldnTan

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Re: Question about a 3.8L
« Reply #11 on: September 20, 2018, 02:21:19 PM »
ENJOY!!!!!
79 solar gold    
461.   Factory 4 speed
PTFB SFC
PTFB 1LE
3.08 rear  for now
Lots O Fun

DeCaff2007

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Re: Question about a 3.8L
« Reply #12 on: September 20, 2018, 05:54:16 PM »
Oh I will.  Also, since I've solved this problem, I went ahead and bought the front struts that it so desperately needs.
1976 T/A 400, 4-speed swap.... 

Check out my resto thread:  http://transamcountry.com/community/index.php?topic=48626.0

It's all trial and error until something lines up...

Re: Question about a 3.8L
« Reply #12 on: September 20, 2018, 05:54:16 PM »
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