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Discussion Starter · #1 ·
Engine misfire after dealer installs new injectors - 1984 GN
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OK so here i am again, hat in hand and praying for help!

I had an extreme rough idle and yet car still performed well at WOT- took 84 GN to a respected GM dealer in a town close to Ottawa, Canada, with a shop foreman who has a great reputation (built a very cool rat rod).

Car diagnosed with a need to replace 29 year old injectors and 29 year old IAC motor.

OK that done and now the car has a misfire (I believe). Idle is better. Car sounds like it is running on four or five cylinders and car shakes from 0-130 kph. If you drive gently the shake/shudder/misfire is most prominent around 75kph when she drops down into overdrive and labours when getting up to speed.

Dealership seems to be at a loss to figure this out and I am frankly getting very discouraged. Car is back in my hands for two weeks before it goes back to the dealer.

Your thoughts and suggestion will be most appreciated.
 

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I'm not an expert with the "84, but it sounds like you have an ignition or electrical issue. Have the coil pack and module looked at. I had similar issues as you and it was the coil pack that went bad. Check your ignition wires as well - make sure each boot is firmly attached to each plug. I hope you find your problem
 

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Discussion Starter · #3 ·
Coil pacs and wires test as OK. All plug wires secure. Car starts, runs and can get from 120 to 140 in no time but car is stuttering from 0 130????????
 

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Discussion Starter · #5 ·
Update

This AM a buddy with 32 years GM experience as driveability guy, and I started to do elimination diagnostics.

Check coils - 11,000 ohms aprox for all three coils
Sparc - used an ST125 to test spark on all all wires - plenty of spark around plug electrodes.
Inserted nails into each coil boot and and shorted out each one in turn - the engine has a stumble to start with and the stumble got worse on 1,2,4,5,and 6 - no worse on #3 - aha moment - number 3 has dead fault.
ECM - brown/purple wires (pin 15 and 16 I think)- 12v key on dropped to zero when tested as is should be for #3 which failed the "stumble" test.
No compression tester handy - adjourned until tomorrow morning.

Looking like no/low compression or a bad injector out of the box.

Update to follow.

Thanx Joe - I had replaced the MAF with a back up I had and drove a few kms with no change at all.
 

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Hope you fond what the problem is. It's a bummer not being able to drive you car.
Just in case, when was your timing chain changed or checked?
 

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Discussion Starter · #7 ·
Duh!!!!!!!!!!!

Sometimes the toughest fault to find is the oine in front off your nose.

Connector to injector on number 1 had broken palstic housing and injector had backed off causing bad misfire.

Fixed now - YEA! - can wash it and drive it again.

:cheers:
 
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