V6 Ignition Guru Needed

[COPO TOM]

I have an 87 GN that I can not get to start because I have no spark at the plugs. This started about 4 months ago with the car running all-right around town, but the car would shut-off if you had your foot in the gas when it reached about 12# of boost ( if you let off the gas the car came right back to running and was fine as long as you were just driving normal. I tried it a couple of times and held the gas pedal to the floor and the car came back once and was pulling hard but I let off immediately ). Then the car started having alot of rich black exhaust smoke all the time. This went on for about a 3 or 4 day period in which the car was driven very little. Next the car would not start at all. I have put a timing light on all of the plug wires an I only get a blink every once in awhile or not at all. When I do get a blink all the plugs must get one because you can hear a difference in they way the engine is cranking, like it wants to start. I have swapped out the ignition module coil pack assembly, computer, cam and crank sensors. I have tried to follow the service manual and have voltage where it says I should, but I still have no spark. I have checked the engines compression and it has 140# to 145#'s. Before the car quit running, but was shutting down, I changed the injectors for 009's and a new chip, and also swapped out the oil pressure switch. I have checked the fuses in the main fuse block that have ignition or fuel pressure listed by them and they are all OK. I though it might be the factory security system, but in checking that on another GN, it only stops the starter from working, and the starter is working fine on the car that won't run. I am open to any and all help and opinons. If you know of any fuses anywhere else, have had a problem like mine, anything that might get me going please reply.

 

[FJM568]

Check the cam sensor and crank sensor wiring harnesses...As someone is cranking the motor over, wiggle the harnesses and see if that helps it any...I had basically the same problem on my 85 GN...engine would torque over and the motor would shut off...When I would finally get it running, with it idling, I would wiggle various wiring harnesses and connectors until I found the one that made the car stall...Fixing it was as simple as ordering a new ign module harness with new pigtails for the cam and crank sensors from John Spina @ Casper's Electronics and splicing it in...

Hope this helps...

 

[COPO TOM]

Thanks, I have tried wiggling the 14-pin ignition connection while trying to start the car, but when it quits raining I will try the other two.

 

[V6 Beast]

Also make sure your Orange ECM(by the battery) wire hasn't come loose or broken.

Sully

 

[COPO TOM]

I tried wiggling the wires today. The orange wire and the cam sensor didn't make any difference. When I wiggled the crank sensor wires the car acted like it was going to start, but didn't. Then no mater where I wiggled the crank sensor wires it never tried to start again. I don't know if wiggling the wires made the difference or if it was just another caes of it trying to start on it's own. The timing light does blink sometimes when trying to start the car on it's own. Thanks for all the help. Does anybody think I need to go ahead and replace the wiring with the kit from Casper?

 

[UNGN]

Originally posted by COPO TOM
I tried wiggling the wires today. The orange wire and the cam sensor didn't make any difference. When I wiggled the crank sensor wires the car acted like it was going to start, but didn't. Then no mater where I wiggled the crank sensor wires it never tried to start again. I don't know if wiggling the wires made the difference or if it was just another caes of it trying to start on it's own. The timing light does blink sometimes when trying to start the car on it's own. Thanks for all the help. Does anybody think I need to go ahead and replace the wiring with the kit from Casper?

Sounds like a crank sensor.

 

[V8 KILR]

I agree with UNGN...check the crank sensor and make sure the clearance is at least .020" on either side of the reluctor ring on the balancer. Also, I think the sensors being made now only work when the reluctor ring passes through the slot in the sensor that's farthest from the electrical connector...I think. Someone please correct me if it's the other slot.

Make sure the sensor is getting proper voltage and that the ground to the sensor is good. You can check both with the key ON, at the sensor harness terminal. If both are good, reconnect the sensor, and monitor the voltage the sensor is sending to the ECM while the engine is cranking with a voltmeter. Check this at the ECM terminals. You should see at least 6 or more volts at terminals B5(crank sensor reference signal) and A11(cam sensor signal) while cranking. Less than this can make the car difficult or impossible to start.

Don't give up. I had a no start condition for about three weeks once and it was due to a failed aftermarket (KEM brand) crank sensor that was only two months old. I did the test above and it pinpointed the problem. Sure wish I did it first! Good luck and let us know what happens.

 

[COPO TOM]

Thanks again for all of your help! I am sure the gap is set at .020 on each side on the crank sensor, as I have a special plastic feeler gauge with twin blades just for setting these. Checking voltage is where I REALLY need help. I did check the voltage at the crank sensor like it said in the service manual, and I did have the voltage it called for, with the engine cranking. But how do I check the ground at the sensor harness? Also, when I check the voltage at the ECM, does the harness need to be disconnected from the ECM, or do I need to probe the wire terminal while it is connected?

 

[V8 KILR]

The black wire of the three making up the crank sensor harness is the ground wire. Hook a test light to the positive terminal of the battery and after you've disconnected the connector from the sensor, touch the light to the black wire's terminal and it should light if the ground is good. If it doesn't light, the wire could be broken somewhere in the harness.

You can leave the harness connected at the ECM while checking terminals B5 and A11. Good luck once again. Keep us informed.

 

[COPO TOM]

Thanks V8KILR! I'll try and check this this afternoon.

 

[COPO TOM]

I checked which slot the reluctor ring went through and it was the one fartherest from the electrical connection. The test light did light when I touched it to the center (black) wire in the crank sensor harness. The lime green wire showed 9.5 v. and the other wire showed 6.75 v. I checked the battery and it only showed 11.75 v. which any bring these other readings down some. I am only showing 4.3 volts on the B5 terminal while cranking the enging. I have 7.2 volts on the A11 terminal. The reading on B5 and A11 were done with booster cables attached from another running auto. Does this wire (from terminal B5) need to be replaced or is there a connection in it somewhere? Again thanks for all your help.

 

[COPO TOM]

Anyone out there that has had this problem before please let me know how you fixed yours. Please! This wiring stuff drives me crazy.

 

[V8 KILR]

Hmmm.....

The voltage on B5 seems a bit low, but I know that the voltage reading will be lower when the vane on the balancer passes through the switch.

The wire that runs from the B5 terminal on the ECM runs directly to the ignition module terminal C, or the third wire on the module harness from the firewall (purple w/ the white stripe).

I would check and make sure the wires aren't broken somewhere by disconnecting both the ignition module harness and the crank sensor harness. Looking at the ignition module harness, terminals F,G, and H (the 6th,7th, and 8th wire from the firewall) are the ones that go to the crank sensor. Attach one end of a wire to the ground on the battery (or any good ground point) and insert the other end into one of the crank harness connector terminals. Then, take a test light hooked to 12V and touch the respective terminal in the ignition harness. Do this for all three wires and wiggle the wires as you go. If the light flickers or doesn't light at all, you've found a culprit.

I know this kind of thing gets frustrating in a hurry, but hang in there. We're rooting for you! Good luck.

 

[COPO TOM]

Thanks again V8 KILR. I won't get a chance to check this for a few days but I will post back what I find out. Also I will turn the engine with a wrench to make sure of the voltage at B5 with the vane both in and out of the crank sensor.

 

[COPO TOM]

Sorry it has been a few days since I last got to work on the GN, but I did get back to it today, and this is what I found. Using a test light I checked Ingnition module terminal [IMT] "C" to ECM terminal "B5" and IMT "D" to ECM "B3", and they checked out alright. I disconnected the crank sensor and checked the wires back to the 14 pin IMT, and they checked out alright. I next disconnected the cam position sensor and checked out the wires back to the IMT, and they checked out alright. Next I checked out IMT "J" to ECM terminal "A-11", and I could not get the test light to light. I tried several more times with someone wiggling the test lead at the ECM while I was at the IMT "J", and never did get it to check OK. This is the same terminal that checked low voltage (4.3 volts) when I was cranking the engine over in a test I run before. This is the cam sensor terminal at the ECM, so does this sound like the problem, and if so how would you go about fixing it? Thanks for all of your help!

 

[Darrell Jackson]

If you are checking for continuity between the 2 terminals and you did not get the test light to come on, what I'd suggest is to get a digital multimeter and measure the actual resistance between the 2 points. By looking at the schematic the wires go from point to point so the resistance should be close to 0 ohms. Disconnect the terminals and take the check. If you get an "open", then get the test light and probe into the insulation on the wiring (tip should be a hard point) with the other end of the test light to one of the connections on the terminal. Do this until you find where the conductor is broken inside the insulation.

Darrell
Stock '87 GN

 

[COPO TOM]

I was checking continuity between the terminals. Using the digital volt meter, what scale should I use to check the resistance. If the resistance is high, does this mean there is corrosion inside the insulation, and the wire will need to be replaced? Thanks again for everyones help!

 

[Darrell Jackson]

Use a low scale. If you are checking from point to point first and you are getting an "open", the problem could be a bad connection at the connector pin with the wire going into it. That's why if you are getting an open at the connector pins then you can probe into the insulation before the wire gets to the connector pins and measure continuity. If you have good continuity when doing this, then this would prove that there is a problem with the connector pin and wiring in the connector pin.

Darrell

 

[COPO TOM]

Thanks! I will try to check this when I get home from work tomorrow.

 

[COPO TOM]

I tried checking the continuity [with an inline digital meter] on the wire that run from the ignition module terminal "J" to ECM "A-11", and the digital meter showed only 0.01 volts. Next I checked resistance on the same circuit and got a constant 1., which I think means an open circuit. I will try and back-probe this wire from the ignition module to the ECM when I get some time next monday. Does this sound like the way to go about checking this problem at this time? Thanks again for all the help!