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'94 Grand Am 3.1L Backfire DTC 77 History #4844629 08/19/18 01:37 PM
Joined: Jan 2004
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benjamming Offline OP
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'94 Grand Am 3.1L with ~ 240k miles. Car was running fine (for a 24 year old car anyway) until immediately after the following general maintenance which happened at one sitting:
Changed engine oil & oil filter
Drained & refilled coolant 6qt
Add cooling system seal tablets
Changed PCV valve
Drained & refilled transmission oil with 6qt ATF & filter
Changed spark plugs Iridium TT

It backfires, stumbles, & has severe lack of power. It stalled a couple times yesterday. Finally got a scan tool with ALDL adapter (don't have a Tech 1) that would read '94 GM OBD1.5 codes (paper clip won't work on this vehicle unfortunately) & DTC 77 was in the history. This is for EGR solenoid #3 malfunction. I could replace the EGR valve which I did at 186k miles with the same code. However, timing seems to suggest something else potentially.

I swapped back to the previous spark plugs which didn't help.
I've pulled all 3 ignition coils & checked secondary resitance which were ~6k & that's within spec according to this data sheet.
It could be the intake plenum is dirty but odd that it would show up right after general maintenance.
Low coolant light is on even though I refilled to full. I've done much more than ever done previously to get out any trapped air if that's an issue.

I would appreciate any insight for what may be causing this problem all of a sudden.

Thanks!

Re: '94 Grand Am 3.1L Backfire DTC 77 History [Re: benjamming] #4844682 08/19/18 02:42 PM
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Blkstanger Offline
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The only system that you touched that could possibly cause this would be the ignition. I'd go back through everything you did changing the plugs. I changed plugs in my Jeep once and had bad misfire. Ended up the little coil spring contacts in the coils had disintegrated.


99 Jeep WJ 4.7 200,000mi. Maxlife 10w30, Fram Ultra.
15 Ford Escape S 2.5
Re: '94 Grand Am 3.1L Backfire DTC 77 History [Re: benjamming] #4844686 08/19/18 02:46 PM
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Nitronoise Offline
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do you have the firing order correct on the coil packs


07 Ford Freestyle 135K
06 Honda Acord EX 115K
04 Hyundai Sonata 290K sold
03 Hyundai Santa Fe 165K
02 Ford Tarus 98K
00 Buick Regal SC 135K
95 Goldwing 28K

Re: '94 Grand Am 3.1L Backfire DTC 77 History [Re: benjamming] #4844687 08/19/18 02:46 PM
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eljefino Offline
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If the "quad drivers" on those primitive ECMs go bad you might not have the power to run the EGR solenoid. Something else could be shorted-- cooling fan relay, etc. Might have a pinched wire. Check that the +5V (or whatever) regulated power from the computer is satisfactory at all the connections you can find.

Re: '94 Grand Am 3.1L Backfire DTC 77 History [Re: benjamming] #4844693 08/19/18 03:03 PM
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dishdude Offline
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Did you pull the plugs one at a time? Agree with previous poster to check firing order. It's also possible one of the wires was damaged when removed from the old plugs.


2018 Challenger SRT 392 PUP 0w-40 Wix 57899XP
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Re: '94 Grand Am 3.1L Backfire DTC 77 History [Re: benjamming] #4844699 08/19/18 03:12 PM
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benjamming Offline OP
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Yes plugs are correct on the coil packs & the correct location there. I didn't touch those until after the problem arose.
I was concerned about plug wire damage but I had changed them 30k miles ago.
I did however, get to thinking after writing all the above, that perhaps I didn't double check the plug wires. I had assumed that I only took 1 off at a time, which I did, but didn't put them back on right away. So, sure enough, #2 & #4 were swapped (first two that I checked - easy ones on the front side thankfully).

Re: '94 Grand Am 3.1L Backfire DTC 77 History [Re: benjamming] #4844703 08/19/18 03:18 PM
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BigD1 Offline
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About the low coolant light. My 92 3.1 has bleeder valves. Did you bleed the cooling system at the thermostat?

The after market low level coolant sensors are junk. I finally said the heck with it, and just unplugged mine, so I did not have to stare at the idiot light.



1992 Toyota Pickup--AmazonBasics Conventional--10W-30--Toyota 90915YZZD1
Re: '94 Grand Am 3.1L Backfire DTC 77 History [Re: benjamming] #4844797 08/19/18 05:58 PM
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BrocLuno Offline
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I'd be checking wiring. As long as you are into this that many years, you know there is plenty of crevice corrosion at all points of contact...

The first thing I'd do is make myself a crimped and soldered ground cable. One lug at the battery negative, one to the engine block, one to teh firewall at a good availbale bolt. Never-Sieze them all and see what happens.

If the ECU can't see a real ground (0v), it can't get correct readings from the sensors. Put everything on new common ground and see what happens ...


Formerly in marine engineering. In an earlier life I owned my own petroleum tank truck, and hauled for the majors and independent's.
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