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1990 Pontiac Grand Am misses

Tiny
EDKINCH
  • MEMBER
  • 1990 PONTIAC GRAND AM
  • 4 CYL
  • FWD
  • MANUAL
  • 45,000 MILES
I have a 1990 pontiac grand am with a 2.3 HO Quad 4 (vin A) engine. Recently after driving it I shut it off and went in a store. When I came out and restarted it, it seemed as if it were running on only 2 or 3 cylinders. I took it home and found a loose spark plug and cracked boot retainer. I replaced the spark plug caps & boots. Put it back together and it ran fine. Drove it about 5 or 6 miles, shut it off, and when restarted it, did same thing. Replaced plugs thinking one maybe had a crack (had new coils & alternator last year). Drove fine until I shut it off, but when restarted, did same thing. Thinking might be ignition module getting hot causes problem (only thing left up there to replace), but even after it cools down it misses until I pull everything apart and then put it back together. Pulled the IDI cover and grounded all plugs while in boots and all seem to fire fine. Exhaust fine, new fuel filter. Totally confused, but I am sure it is ignition related.
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Tuesday, August 12th, 2008 AT 11:34 AM

8 Replies

Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
Check compression and injector for thoses cylinders
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Tuesday, August 12th, 2008 AT 11:38 AM
Tiny
EDKINCH
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  • 4 POSTS
Compression fine. Checked injectors - fine also. Cylinders 1 & 4 both missing (exhaust manifold not getting hot). Switched coils from 2 & 3, no effect. Plugs dry. Obviously not getting fuel to those two cylinders, which leads me to believe no electrical impulse to injectors (haven't got to checking that far yet). How/Where do I go now?
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Tuesday, August 19th, 2008 AT 9:51 PM
Tiny
RASMATAZ
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If you got power at 1/4 injector harness gray wire and its not pulsing-you have a problem with the injector driver in the computer-see below


http://www.2carpros.com/forum/automotive_pictures/12900_injector_1.jpg



Good Luck
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Tuesday, August 19th, 2008 AT 10:04 PM
Tiny
EDKINCH
  • MEMBER
  • 4 POSTS
Here's the latest. Pulled out my GM service manual and went through series of tests. At three pin connector from ecm test light blinks for both blue and green wires when grounded to gray. Checked resistance of injectors (should be under 3 ohms). One was 2.7 and other was 1.3, so should be okay. Grounded gray wire with test at each injector connector. Test light blinked on #4, but not on # 1. While checking for electrical pulse to # 1 connector, noticed engine ran smoother and # 4 was now firing (exhaust manifold getting hot). When I re-connected # 1 injector connector, both cylinders now misfired. Other series of tests tended to point to faulty ecm. Maybe a short to # 1? Why would connecting # 1 cause # 4 to stop firing, but # 4 fine with # 1 disconnected? This problem has made me lose sleep!
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Wednesday, August 20th, 2008 AT 10:26 AM
Tiny
RASMATAZ
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Sounds as though between injector 1/4 its dragging down the other-


http://www.2carpros.com/forum/automotive_pictures/12900_injector_2.jpg

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Wednesday, August 20th, 2008 AT 10:37 AM
Tiny
EDKINCH
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That may be true, but if they are connected in parallel (which I assume they are) then the equivalent resistance would be 2 ohms, which is what is expected as per your chart. I am going to check for a short or discontinuity in injector # 1 connector, but I still don't see how that would affect # 4 to the point of misfiring.
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Wednesday, August 20th, 2008 AT 11:12 AM
Tiny
RASMATAZ
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In a parallel circuit the resistances are always less than what they are-

Disconnect the injector harness and the PCM connector and check the wiring for short and open-no wirng problem its between the injector and computer
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Wednesday, August 20th, 2008 AT 12:25 PM
Tiny
EDKINCH
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No shorts or opens. Swapped out #1 & #2 injectors. Now #2 & #3 aren't firing. Think I found the problem. According to the manual, as long as the injector had no more than 3 ohms resistance but not zero, it should be okay. All other injectors have about 2.6 ohms, and the 'bad' one has 1.5. I wouldn't think too much current would make it now fire, but that seems to be the case. I am going to pick up a new injector and pray for the best!
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Wednesday, August 20th, 2008 AT 2:14 PM

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