1989 Jeep Wrangler no spark

Tiny
ROBERT THE ROBOT
  • MEMBER
  • 1989 JEEP WRANGLER
  • 2.5L
  • 4 CYL
  • 4WD
  • MANUAL
My pastors jeep got towed to me I know somewhat about cars i'm an old school tec. I'm not getting spark out of coil? Tried crank shaft sensor no start coil getting 12 v with key on not sure what to try next? Don't want to keep throwing parts at it? Im not getting a check Eng light when key on I have to ask him if he knows if it use to come on? Or SOME ONE SAID IT COULD BE IN THE DIST? How do I test that? Thanking you in advance Robert
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Saturday, June 20th, 2015 AT 1:24 PM

4 Replies

Tiny
CARADIODOC
  • EXPERT
The most likely suspect is the ignition module.

You also have to check if the fuel pump runs during engine cranking. The majority of "cranks / no-starts" are caused by a loss of spark and fuel pressure, but the fuel pressure can be misleading because the fuel pump will still run for one or two seconds when the ignition switch is turned on.
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Saturday, June 20th, 2015 AT 7:40 PM
Tiny
ROBERT THE ROBOT
  • MEMBER
Thank you so much I will take the ign module out of the dist and have it tested. As far as FUE LThe 1st thing I did was put some carb cleaner in intake and no start then I checked for spark no spark Thanks again Robert
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Sunday, June 21st, 2015 AT 1:34 PM
Tiny
ROBERT THE ROBOT
  • MEMBER
Please help on that 2.5 wrangler is the icm under dist cap or is it a box on the firewall somewhere? Looking at pic's of the part it looks like a box? Thanks
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Sunday, June 21st, 2015 AT 5:26 PM
Tiny
CARADIODOC
  • EXPERT
Yup, it's a box. I use the Rock Auto web site a lot for reference. They will show what it looks like.

I'm REAL familiar with Chrysler product Jeeps, but yours is still full of AMC stuff. It DOES have a very tough Chrysler transmission but I think the ignition system is Ford's. Your generator is a holdover of GM's very nice '86 and older version. Luckily it's not the '87 and newer redesigned pile.

The best I can do is describe how the Chrysler system works. You'll have to substitute some terminology to suit your vehicle. The Engine Computer turns the automatic shutdown, (ASD) relay on for one second when the ignition switch is turned on. That is to run the fuel pump to insure fuel pressure is up for starting in case it bled down over a few days. After that, the relay is turned on again when the computer sees engine rotation, (cranking or running). It knows that by the pulses it receives from the crankshaft position sensor and the camshaft position sensor. Your cam sensor is inside the distributor.

The ASD relay sends current to the ignition coil, (or coil pack on newer vehicles), injectors, fuel pump or pump relay, oxygen sensor heaters, and alternator field. You can monitor that voltage at any of those places. On Chryslers, that is the dark green / orange wire. If yours is different, just look for the wire color that is the same at the ignition coil and all the injectors. You can use a digital voltmeter, but most of them respond too slowly to pick up that initial one-second pulse. A test light works better for this. You should see 12 volts on any of those points for one second when you turn on the ignition switch, then it will go away. If you see that, the 12 volt feed circuit and relay are okay, and the computer has control of that relay.

Most of the time you do get that one-second pulse, but next, the 12 volts must come back during cranking. That is what's missing about 95 percent of the time. This is almost always due to missing signal from the cam or crank sensor. If that voltage DOES come back during cranking, that's when you have to determine if you're missing spark OR fuel pressure. On Chryslers, that is usually a dead fuel pump. The clue there is it also won't run for that initial one second so you will have 0 psi on the fuel rail test port. You will have spark yet.

Missing spark is the cause of no-starts about one percent of the time, but since you have a separate ignition module, I'm not familiar with its record for reliability. I suspect those don't cost very much, so this is one of the few times I would be willing to just try a new one, and put it on the shelf for future use if it doesn't solve the no-spark.
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Sunday, June 21st, 2015 AT 8:57 PM

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