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1991 "no start" case

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PGP1991

New member
Hi all! I'm new here and I live in Finland, so I hope you'll understand my grammatical mistakes..! :D

The reason why I have to ask you about, is that I don’t actually know what to do next. My car is 1991 Pontiac Grand Prix 3.1 VIN:T and engine doesn’t run at all.
Couple weeks ago I think that I have to replace new spark plugs because this is new car for me and I don’t know previous service history. I put a new plugs and that was the beginning for the problems. Before that it runs really good! I’m a car mechanic so I think that I know something about this. :)(Since then, I have already changed the second one spark plugs.)

So the engine won’t fire up anymore. At this moment it cranks good but won’t start. Sometimes when I try to crank it, the engine hit back like ignition timing would be too early. And sometimes it popping into the intake manifold. Exhaust gas smell like really rich mixture and smoke is gray-black.

Things what has been replaced:
-Repl. new crank position sensor. (there is only one for it)
-Repl. new coolant temperature sensor.
-Repl. new ignition module and also all coils.
-Repl. new fuel pump relay
-Repl. new spark plugs and also tried to new spark plug wire
-Repl. new battery

Things what has been done:
-Cleaned EGR valve.
-Cleaned throttle body.
-Checked all vacuum lines
-Checked timing mark
-Checked injectors resistance, one had to be replaced. Resistance was 5.1 ohm.
-Checked wire harness from ecm to injectors, map.. etc..
-Tested sparks (for all plugs)
-Checked fuel pressue
-Tested 5volt system
-Tested ICM ground and also main power socket (the driver side one socket)
-Tested TPS
-And many little things..

Any idea what to do next? We have sparks. We have fuel pressue. We have power to crank the engine and I have tired to try! :th_scratchhead: All ideas are very welcome! So if you know something, please let me know!

Many thanks,
J-P
 


Today I double check all wires from ECM to injectors. Those are 100% OK. Then I plugged back all socket on right position (except for the injectors) and test injectors battery +. It was OK. Then I tested the injectors connection to the ground and that connection should not be have. Still I found about 80 KOhms resistanse for it. If there is a connection, service manual says: Replace ECM.

But then I found this one:

91gpse said:
does it sound like its backfiring? or is there a popping sound in the intake? because thats what my 91 3.1 mpfi did until it stopped running. it stalled one day when it got to operating temp and wouldnt refire then the next day when it was cool it fired right up. until it finally just wouldnt start anymore and it sounded like it was backfiring. check for black soot in your air filter. Edit: i replaced everything that monzaman mentioned and more until i figured out it was a twisted camshaft. so im rebuilding it right now
Click to expand...

It sounds like exactly same problem! I have to check this before I order a new ECM. Timing mark is still OK, but if it is twisted.. Is it possible to happen?
Interesting!
 
OK, little update..

My camshaft is OK. I took front valve cover off and turn timing mark correct place. So then I can calculate that the 6th cylinder should be have just end of the induction stroke. And it has.

So, I must to order new ECM and hope best! Let see!
 
OK.. In my case the problem was faulty (new) ignition coil module. And also MAP went broken because it backfire so much. What does we learn from this? Also new parts may be broken.

Anyway, the engine runs very well at this moment.
 
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