The computer won't signal the ignition coil to spark unless it's happy with the signals from the crankshaft position sensor and the camshaft position sensor.
Hey! Just jumping in here. I need to replace my crankshaft position sensor, but I have no pigtail. So I only have 3 exposed wires and I dont know how to wire the sensor. I am sure it matters, is there any way of knowing how to wire it without the pigtail/connector.
The ignition coil receives its +12v from the ASD (auto shut down) relay inside the power distribution center. The ASD relay is controlled by the computer and it won't energize the ASD relay until it's happy with all of its required signals like I mentioned above.
Short update.
The ignition coil isn't getting any voltage so I guess the coil itself is not the problem. The crankshaft position sensor has been replaced when the "no spark problem" appeared.
The ASD relay has been swapped with the one from the horn (same specs).
I hate to just throw parts at problems but assuming the crankshaft position sensor is good, my next suspicion would be the camshaft position sensor.
You do hear the fuel pump briefly turn on/off when you first turn the ignition on right? That will at least confirm the ASD circuit is working since the ASD relay also provides the fuel pump's power.
Thank you Jerry for trying to help.
Yes, I can hear the fuel pump and I can feel a click when I put my finger on the ASD relay when somebody else turns the ignition on.
Does the coil receive +12v during the brief time the fuel pump is on and then shut off when the fuel pump shuts off? If so, that still leads me to suspect a bad sensor.
The entire distributor unit including the camshaft sensor had been replaced two weeks ago when we worked on the bucking problem. But this is now an entire new level with no spark at all.
Yes go ahead jump plus 12 to coil and see if it starts because if it does the PCM is happy with the crank angle sensor and sending out ground pulses to coil to fire spark
I would also look at wiring diagram and work backwards from coil plus 12 to see where it drops off
Can also do a temporary jumper in place of ASD relay
No way crank or cam sensor stopping the 12 volts as that comes on before cranking when no pulses from either sensor so don't think Jerry is leading you in right direction now that we know no 12 volt positive with key on
The coil receives 12.xV for a split second and then it drops to near zero.
We've tested the camshaft sensor and it didn't show bad behavior. After the test the engine could be started, it ran for a few minutes and then died. Not starting up again since then and again no spark.
Guys, thank you so much for all the support. I very much appreciate it. Please keep the ideas coming and I'll test whatever I can.
Try a jumper replacing ASD relay main terminals not the relay magnet control but the main in and out and see if that gives a constant plus 12 to coil with key on
If it does then most likely PCM is not tripping the relay but if it does not then it is a problem else where (all assuming you had a known good relay)
Also all wranglers and especially early ones are prone to ground issues so just make sure back of block to firewall ground is intact relatively clean and tight on both ends
Try a jumper replacing ASD relay main terminals not the relay magnet control but the main in and out and see if that gives a constant plus 12 to coil with key on If it does then most likely PCM is not tripping the relay but if it does not then it is a problem else where (all assuming you had a known good relay) Also all wranglers and especially early ones are prone to ground issues so just make sure back of block to firewall ground is intact relatively clean and tight on both ends
Went out to the vehicle this morning. Without doing anything to it, I started the engine and it ran for about 3 seconds, then died.
We then cleaned all the ground contacts we could find and the main battery connectors as well.
Then started and the engine fired up within the first second and ran smoothly for 2 to 3 minutes, then all of a sudden, and without doing anything, died again.
Now it sometimes starts, mostly it doesn't.
Seems like it sparks only occasionally.
We'll try to jump the ASD relay now to see if that tells us anything.
There are two wires (green one and white one) going into the coil.
As I understand it the white wire is supposed to have 12V and the green one is the pulsing signal wire.
When I test the white one against ground there's basically no voltage (7mV). When I test it against the plus pole of the battery it shows 12.4V.
However when I test it for resistance against the ground it gives me 107kOhm.
Then I tested the green wire against ground, I only have a digital multimeter, and it gave me a reading of 10.2V only when cranking the engine.
After all that testing I tried to start the engine. It fired right up and ran smoothly. I turned it off after maybe 7 or 8 minutes. Turned it back on seconds later without any problems. Then I got the idea to drive to the next gas station. It started bucking after a ¾ mile and died 20 seconds later. Didn't get it to start up again and we had to push it home.
You have a ’98, right? If so the coil wires should be orange/dark green (may look only green) which is the battery power (+) wire & grey (may look white) which is the pulsing ground (-) wire that the PCM uses to fire the coil.
If you get 12v to the coil (+) for 2-3 seconds after turning the key on but then nothing that is normal but if you get nothing when cranking the engine (key in start position) that is not normal & it is not a fuse or relay problem. The PCM will open the ASD & fuel pump relays if it does not see a crank sensor signal when cranking. It does this by opening the ground path to the relay coils which opens the relay contacts & kills (+) power from the relay to the coil/injectors. So either the sensor is bad, a bad wire to or from sensor to PCM, or the PCM is bad.
You can try bypassing the relays as noted above but may have to do both ASD & FP relays. Try the ASD first but if no start, leave the ASD jumped & also jump the FP relay. Jump between the 30 & 87 terminals in the relay sockets. The terminal numbers should be printed on the side of the relays if they are the originals. If it starts with the jumpers the PCM is bad. There is a possible work around if that is the problem.
If the gauges are not coming up with the key on (when it is not starting) that can also indicate a PCM problem.
There's a threaded stud at the rear of the valve cover, passenger side, that is capable of rubbing through the insulation of the wiring harness that passes by right next to it. At this point I'd take a good look at that wiring harness and check for signs of damage.
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