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fiveoformula Member
Joined: 08 Aug 2007 Posts: 1799 Location: OR
1988 Pontiac Formula
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Posted: Fri May 07, 2010 11:07 am Post subject: School project |
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Over at PCC Im in engine performance class, we have a customer car that myself and my buddy are working on. Its an '87 Iroc TPI 5.0 automatic.
The complaint is "runs only with distributor unplugged".
We found that they were refering to the EST wire, and it stays running no problem with it unplugged but if you plug it back in and fire it up, pretty much dies once it comes down to slow idle. We've checked the IAC and the MAF, fuel pressure is also good. Just trying to come up with any other ideas so we can tackle it on monday. What would you guys check? _________________
'88 FORMULA |
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Twilightoptics Hardcore (12sec Club)
Joined: 13 Jan 2004 Posts: 9191 Location: Auburn , WA
1987 Chevrolet Camaro IROC-Z
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Posted: Fri May 07, 2010 11:28 am Post subject: |
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Try unplugging other sensors to put the car in Limp Home mode just like disconnecting the EST does.
Verify that the timing is right (why was the EST unplugged in the first place)
Then make sure the pickup coil is doing it's job.
Then I'd replaced the ignition module hoping the ECM isn't the culprit. _________________ A redline a day keeps the carbon away! |
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91RSVert Member
Joined: 16 May 2007 Posts: 2736 Location: AR
1991 Chevrolet Camaro RS
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Posted: Fri May 07, 2010 12:09 pm Post subject: |
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Not to doubt twilight, but my understanding of the pickup coil or IM system, if neither is working, it wont run period? But if you have the tools to test, test them to "eliminate" from the problem list.
I would look to see if the balancer has spun on the crank hub giving false timing readings. I saw this happen on a few v6 cars. |
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aaron_sK Member
Joined: 23 Jan 2006 Posts: 8834 Location: Back in beautiful Tacompton
1987 Chevrolet Camaro IROC-Z
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Posted: Fri May 07, 2010 3:09 pm Post subject: |
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91RSVert wrote: | Not to doubt twilight, but my understanding of the pickup coil or IM system, if neither is working, it wont run period? |
Car will run with a bad pickup, and possibly a bad module. Bad pickup will cause misfire, or late fire. Hell, Tony drove his GTA to Cows a few years back with the pickup coil that came out in pieces.
91RSVert wrote: | I would look to see if the balancer has spun on the crank hub giving false timing readings. |
Your school shop should have a dead-stop, so this would be very easy to eliminate.
In my experience it is cheaper to buy a loaded reman distributor than it is to buy a pickup coil and ignition module separately. Your school might not appreciate throwing parts at the problem, however, even if it results in less outlay of cash. |
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86toy Member
Joined: 20 Jan 2010 Posts: 61 Location: tacoma
1986 Pontiac Trans Am
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Posted: Fri May 07, 2010 3:43 pm Post subject: |
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The ecm is crap,its running in basicly test mode, which is where you adjust the base timing and idle speed if needed. _________________ 86 t/a 305 tpi 700r4 3.73 possi 4 wheel disc
245/45/17 restoring |
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chevymad Master B
Joined: 11 Jan 2004 Posts: 5474
1987 Pontiac Formula
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Posted: Fri May 07, 2010 4:29 pm Post subject: |
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A weak pickup coil will cause this too. A pickup coil is basically just a small generator. When it goes bad it sometimes can't produce enough voltage/signal to run the module and the ecm at the same time. Disconnecting the est wire drops the load requirement and allows the engine to run on the module only.
So Paul is right that it could be the problem.. maybe... LOL |
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fiveoformula Member
Joined: 08 Aug 2007 Posts: 1799 Location: OR
1988 Pontiac Formula
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Posted: Fri May 07, 2010 8:26 pm Post subject: |
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Cool that gives me some idea's, I forgot to say that we checked the pickup coil pattern on a lab scope, it had a nice consistant pattern. I did also unplug the MAF and start it. If I remember right it still died. Also i could easily grab another module from some other engine and try it. But like someone said the teacher's don't like us throwing out parts on it... _________________
'88 FORMULA |
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91RSVert Member
Joined: 16 May 2007 Posts: 2736 Location: AR
1991 Chevrolet Camaro RS
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Posted: Sat May 08, 2010 3:55 am Post subject: |
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aaron_sK wrote: |
Car will run with a bad pickup, and possibly a bad module. Bad pickup will cause misfire, or late fire. Hell, Tony drove his GTA to Cows a few years back with the pickup coil that came out in pieces.
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Wow, didnt know it would run. I know when the module overheats, it wont run. I had to make a 23 mile trip stopping every 3 miles and letting it cool off. |
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Xophertony Rodeo Queen
Joined: 13 Oct 2005 Posts: 5304 Location: Portland, Oregon.
1988 Pontiac GTA
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Posted: Sat May 08, 2010 9:24 am Post subject: |
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aaron_sK wrote: | Hell, Tony drove his GTA to Cows a few years back with the pickup coil that came out in pieces. |
sigged
and i would also like to say...
_________________ 86' firebird (Junked in 2015). 88' GTA (sold in 2020).
aaron_sK wrote: | Hell, Tony drove his GTA to Cows a few years back with the pickup coil that came out in pieces. |
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83Z28BlackBetty Bam-Ba-Lam
Joined: 13 Mar 2006 Posts: 2083 Location: Aloha
1983 Chevrolet Camaro Z/28
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Posted: Sat May 08, 2010 8:13 pm Post subject: |
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HAHAHAHAHAHA As soon as I forget all about that picture Tony never fails to post it up again!
~JAKE _________________ 1983 Z-28 5.7 LT1, T56, Headman headers, BW 9 Bolt Posi Disc, WS6 suspension
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aaron_sK Member
Joined: 23 Jan 2006 Posts: 8834 Location: Back in beautiful Tacompton
1987 Chevrolet Camaro IROC-Z
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Posted: Sat May 08, 2010 8:25 pm Post subject: |
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83Z28BlackBetty wrote: | HAHAHAHAHAHA As soon as I forget all about that picture Tony never fails to post it up again!
~JAKE |
Frikkin' eh! |
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fiveoformula Member
Joined: 08 Aug 2007 Posts: 1799 Location: OR
1988 Pontiac Formula
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Posted: Thu May 13, 2010 5:50 pm Post subject: |
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Thought you guys might like to know, we figured this thing out last week. Nobody believed me when I said I thought the problem was the module.... But sure enough it was after we were chasing other things- checking injectors, and the MAF, and the customer even had a spare computer we tried.
The really wierd thing was that the first module we tried, it fired up and took a little bit of running to start running good but eventually it smoothed out really nicely. We figured it's all fixed, and our instructor wants to order a new module for it since the one we put in was just one that we had lying around (GM brand), so we get an aftermarket unit from Baxters and through it in.... Runs crappy, dies ten seconds after start, Tach freaks out, hestitates in higher RPM's too. Just like it did before.
Rip that one out, install the used GM one again and boom, Runs good.
So we found that this Iroc only likes GM modules for some reason... the one we originally pulled also happened to be an aftermarket...
Anyone else have a problem with aftermarket ign. modules? _________________
'88 FORMULA |
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Twilightoptics Hardcore (12sec Club)
Joined: 13 Jan 2004 Posts: 9191 Location: Auburn , WA
1987 Chevrolet Camaro IROC-Z
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Posted: Thu May 13, 2010 5:59 pm Post subject: |
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Lots of aftermarket ignition modules and electronic components suck ass _________________ A redline a day keeps the carbon away! |
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aaron_sK Member
Joined: 23 Jan 2006 Posts: 8834 Location: Back in beautiful Tacompton
1987 Chevrolet Camaro IROC-Z
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Posted: Thu May 13, 2010 8:17 pm Post subject: |
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Twilightoptics wrote: | Lots of aftermarket ignition modules and electronic components suck ass |
Lost a TFI module in the Thunderbird a few years ago (common problem on those cars, Ford got sued over it too ). Bought a new one at Baxters, all was well. Few months later starts doing it again. Went to Pull-A-Part and bought a Motorcraft unit that had 110K on, nary a problem since.
This is especially an issue if you do what I did and buy the crappy 'Standard' made in China brand. |
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Xophertony Rodeo Queen
Joined: 13 Oct 2005 Posts: 5304 Location: Portland, Oregon.
1988 Pontiac GTA
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Posted: Sun May 16, 2010 11:17 pm Post subject: |
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83Z28BlackBetty wrote: | HAHAHAHAHAHA As soon as I forget all about that picture Tony never fails to post it up again!
~JAKE |
i do what i can when i can. |
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fiveoformula Member
Joined: 08 Aug 2007 Posts: 1799 Location: OR
1988 Pontiac Formula
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Posted: Tue May 18, 2010 9:46 pm Post subject: |
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Tony, your ARE the MOST random person I've ever met. lol |
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