3.1 Engine miss on Cyl 2 & 3
19k40rocky
07-19-2010, 09:27 PM
I have an 90 Grand Prix with a 3.1 that starts up fine and runs fine for about a minute or two then starts missing on cylinders #2 and #3. I used an induction timing light to find the missing cylinders. The bad two cylinders flashed about half as much as the good ones. I checked all the coils secondary resistance before and after startup and they had between 6 & 7 thousand resistance. I didn't get the engine vaccum checked when it was running good, but after it started missing on those two cylinders it was running about 16 inches of vaccum. My son replaced the ignition module about a year ago so am thinking that shouldn't be the problem. Any ideas? I keep thinking it has to do with something these two cylinders have in common but not sure. Any help would be greatly appreciated.
3100
07-20-2010, 02:32 AM
-dirty injectors, but I would recommend scan tool verification for misfires.
-2 and 3 don't share the same head, check injector resistances (min 11.8 and max 12.6 ohms)
-tell me what happens when O2 for AF ratio is disconnected, is engine idling any better?
135
246
-2 and 3 don't share the same head, check injector resistances (min 11.8 and max 12.6 ohms)
-tell me what happens when O2 for AF ratio is disconnected, is engine idling any better?
135
246
19k40rocky
07-20-2010, 10:57 PM
Thanks for the reply. I wasn't able to get to it tonite as ended up had to work late. Got a couple probably dumb questions though. Does the dirty injector affect the firing rate of the spark plug? I have an OTC 4000 but I'm not sure it this one is new enough to throw a misfire code. I think it is still OBD I. Also did I understand you want me to unplug the O2 sensor? let me know. Thanks again for helping with this!
3100
07-21-2010, 12:23 AM
Thanks for the reply. I wasn't able to get to it tonite as ended up had to work late. Got a couple probably dumb questions though. Does the dirty injector affect the firing rate of the spark plug? I have an OTC 4000 but I'm not sure it this one is new enough to throw a misfire code. I think it is still OBD I. Also did I understand you want me to unplug the O2 sensor? let me know. Thanks again for helping with this!
- that is correct, try disconnect O2 sensor (not the one by cat. converter)
- your vehicle is 1990 so it is OBD1
- that is correct, try disconnect O2 sensor (not the one by cat. converter)
- your vehicle is 1990 so it is OBD1
tblake
07-21-2010, 10:11 AM
I forget the 3100.
Is the plug wires for #2 and #3 going to the same coil? Try swapping the coils around to see if the problem follows.
Is the plug wires for #2 and #3 going to the same coil? Try swapping the coils around to see if the problem follows.
3100
07-21-2010, 01:47 PM
I forget the 3100.
Is the plug wires for #2 and #3 going to the same coil? Try swapping the coils around to see if the problem follows.
because of the crankshaft and DIS system for waste spark, they can only be
1/4 6/3 2/5
Is the plug wires for #2 and #3 going to the same coil? Try swapping the coils around to see if the problem follows.
because of the crankshaft and DIS system for waste spark, they can only be
1/4 6/3 2/5
19k40rocky
07-22-2010, 09:51 PM
I disconnected the O2 sensor and there was no change in the idle or the missing after it warmed up. I had the monitor hooked up to it and the 02 volts were around .45 to start with then built up to about .80 after minute or when was in open loop. Again it started and was hitting solid on all 6 cylinders but gradually after about a minute you could hear those 2 cylinders getting weaker (coincided with the increase in volts) then it went to closed loop and the volts dropped back down to around .47. I unhooked the O2 sensor at that point and it made no changes irregardless of what I did. Also I checked the vaccum at start up and it was the same as when it was missing. I checked for trouble codes and was nothing. Let me know what you think. I really appreciate your help and input on this!
tblake
07-22-2010, 11:13 PM
Try ohm checking the injectors. The should all be approx 12.7 ohms. A little more is ok. Any less and it may be a concern.
19k40rocky
07-23-2010, 10:30 PM
I checked the injectors and this is what I got: #1=10.3 #3=12.6 #5=2.7 #2=12.6 #4=12.5 #6=12.5 Am I correct to assume #1 & #5 are what is causing my engine missing after a few minutes of running? Only question I got is what was up with what looked to be #2 & #3 missing? Let me know. Thanks again for all your help on this!
tblake
07-24-2010, 10:25 AM
Yes, 1 and 5 need replacement.
And tell me again how you verified that 2 and 3 were the missfiring cylinders?
One possiblility is that the injectors on your car are batch fired. Meaning a whole bank of injectors are fired at the same time. If one injector has less resistance than the rest, all the current will travel through the lower resistance injector (or injectors) in your case rather than flowing to the other injectors in the circuit. Thus not firing other cyliners. Electricity will take the path of least resistance.
I would replace #1 and #5 injectors, all injector o-rings, and the upper intake gaskets.
And tell me again how you verified that 2 and 3 were the missfiring cylinders?
One possiblility is that the injectors on your car are batch fired. Meaning a whole bank of injectors are fired at the same time. If one injector has less resistance than the rest, all the current will travel through the lower resistance injector (or injectors) in your case rather than flowing to the other injectors in the circuit. Thus not firing other cyliners. Electricity will take the path of least resistance.
I would replace #1 and #5 injectors, all injector o-rings, and the upper intake gaskets.
19k40rocky
07-24-2010, 10:34 AM
I will replace those and let you know how it works. Barring any interuptions hopefully by the end of the day. I had checked the ignition by using a Sun inductive timing light. I hooked it onto each wire and pulled the trigger. 2 & 3 were flashing about half the pulses of the rest of the cylinders. they all flashed the same at first when it was running right.
3100
07-24-2010, 12:42 PM
then try swapping coils around to see if that will change anything.
19k40rocky
07-25-2010, 07:19 PM
I got the injectors changed and it seems to run fine now. I checked the wires all again for the heck of it and got the same response with the timing light flashes. But it seems to run fine for now. I will drive it for a few days and make sure, but that seemed to fix it. Thanks for all your help on this. Hope I can return the favor sometime.
3100
07-25-2010, 11:04 PM
I got the injectors changed and it seems to run fine now. I checked the wires all again for the heck of it and got the same response with the timing light flashes. But it seems to run fine for now. I will drive it for a few days and make sure, but that seemed to fix it. Thanks for all your help on this. Hope I can return the favor sometime.
Good work but If you did all my tests (post #2) the first time, you would have this problem solved 7 days ago :icon16:
Good work but If you did all my tests (post #2) the first time, you would have this problem solved 7 days ago :icon16:
tblake
07-26-2010, 12:35 AM
Haha good point 3100, but At least the problem got solved.
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