98 Wrangler, No Spark, No Codes...

[tardis454]

Ok.. My wifes 98 Wrangler (2.5L Auto) has been stalling on occasion for a few months, but always restarts fine.
Except for this morning when wifey backed onto the road, drove about 10ft & it died. No restart.

So far I tested...

Fuel pressure at the rail, got 50lbs, its fine.
I got cam/crank signal & injector pulse, (didn't check if the cam/crank are in sync).
Tested the coil, it's perfectly in range both ways.
I checked all of the grounds & the engine bay fuse box/fuses, they are ok.
Car has fresh tune-up too...

I'm using a Snap-On 2500 series Scanner.
The diagnostics index says "No Spark, No Codes" indicates a fault in the ignition module built into the PCM, but also states the ignition module rarely fails(yeah right).

As stated there is no codes & no spark...
I've sold a few 98-up Jeep PCM's at the junkyard I work at, but the most common issue I've seen with Jeeps are bad crank sensors.

Any ideas???

[dieselgeek]

Re: 98 Wrangler, No Spark, No Codes...

If it's the crank position sensor, you can confirm by watching fuel pressure when cranking. At key on, rail pressure should go up (fuel pump primes for 2 seconds). Once you start cranking, fuel pump should come back on again as the PCM sees RPM. If the pump isnt' coming back on when cranking, it's a giveaway that the PCM isnt' seeing RPM.

If you have a scanner that can read OBD live data, you can crank the starter and look for RPM in the live data. No RPM, mean crank sensor problem... I'd see if you can nail it down this way first before swapping a PCM,


-scott

[HoosierGTA]

Re: 98 Wrangler, No Spark, No Codes...

I'd work backward. Make sure your rotor isn't coroded(mine was) check the control module in the distrib.Auto zone/advance auto will do for free(have them test it 6-7 times to ge it good and hot. If not there you may as well test the pick up coil. I say test if your smart with the electricial diagrams in the back of shop manuals. (I'm not so I replace them) Still cheapper than a real mechanic! Good luck !!

[SpiderGearsMan]

Re: 98 Wrangler, No Spark, No Codes...

pain in the ass crank sensor
it is easier on wranglers than cheerykees

[tardis454]

Re: 98 Wrangler, No Spark, No Codes...

Read through the Mitchell procedures, & determined the PCM is bad :c(
The coil, wiring & sensors test fine, the PCM isn't sending juice to the coil at all.
My guess is the ignition module in the PCM crapped out.
I'm ordering a PCM on Monday so we shall see...
Thanks for your help guys, I'll keep you posted.

Edit, I might sneak a crank sensor in first just to be sure!

[dieselgeek]

Re: 98 Wrangler, No Spark, No Codes...

Read through the Mitchell procedures, & determined the PCM is bad :c(
The coil, wiring & sensors test fine, the PCM isn't sending juice to the coil at all.
My guess is the ignition module in the PCM crapped out.
I'm ordering a PCM on Monday so we shall see...
Thanks for your help guys, I'll keep you posted.

Edit, I might sneak a crank sensor in first just to be sure!

You might want to double check that crank sensor. There would be *no* "juice" to the coil without a valid RPM signal during cranking. And the only juice would be a super tiny 5v pulse that you aren't going to see with a voltmeter - an oscilloscope would work, does your snap on scanner have a scope/trace function?

Or you could go the TC route and just start swapping shit out and proclaim yourself awesome when it starts working again ;)

[tardis454]

Re: 98 Wrangler, No Spark, No Codes...

Read through the Mitchell procedures, & determined the PCM is bad :c(
The coil, wiring & sensors test fine, the PCM isn't sending juice to the coil at all.
My guess is the ignition module in the PCM crapped out.
I'm ordering a PCM on Monday so we shall see...
Thanks for your help guys, I'll keep you posted.

Edit, I might sneak a crank sensor in first just to be sure!

You might want to double check that crank sensor. There would be *no* "juice" to the coil without a valid RPM signal during cranking. And the only juice would be a super tiny 5v pulse that you aren't going to see with a voltmeter - an oscilloscope would work, does your snap on scanner have a scope/trace function?

Or you could go the TC route and just start swapping shit out and proclaim yourself awesome when it starts working again ;)

I don't own a scanner, my friend brought his over. Snap-On 2500 (Red Brick)
We hooked it up & ran it through 5, 10 second crank cycles,
These are the scanner results...

No Codes
Shows RPM, has injector pulse, good fuel pressure
Crank & Cam sensors functioning (scanner detects movement)
I do not recall if the cam/crank sensors were sync'd.

Other...

Replaced cap & rotor, old cap & rotor were burnt, charred, corroded (bad pick up coil?)
Inspected pick up coil, appears normal, terminals were slightly corroded
Tested spark to plugs & coil. spark is very weak & dies
Coil tests fine both ways, wire from PCM to coil tests fine
Tested crank sensor, shows infinite resistance
Inspected fuse box, wiring to fuse box
Inspected PCM connectors & terminals

Still have, no spark, no codes...

Anyone know how to test a PCM? lol

[TC]

Re: 98 Wrangler, No Spark, No Codes...

If you have a very weak spark then the coil is getting a signal(because it's sparking), it's just not putting out the voltage. Make sure the coil is getting the correct voltage to it and if that checks out ok, I'll put my money on the coil being bad.

[dieselgeek]

Re: 98 Wrangler, No Spark, No Codes...

The details above show that your crank/cam sensing is working fine.

If the ignitor is "built in" to the PCM, that sucks! at this point I am starting to agree that the ignitor is bad (sometimes called power transistor, or Ignition Control module).

Can you manually trigger the coil and get a nice hot spark? (power to one side, and SHORT tap to ground on the other, should produce a nice hot spark at the end of the coil wire)

Ignitors are easily killed with bad cap & rotor, so, you are definitely on the right track.

[IRONHEAD]

Re: 98 Wrangler, No Spark, No Codes...

The details above show that your crank/cam sensing is working fine.

If the ignitor is "built in" to the PCM, that sucks!

The wonders of E.F.I..

[dieselgeek]

Re: 98 Wrangler, No Spark, No Codes...

The details above show that your crank/cam sensing is working fine.

If the ignitor is "built in" to the PCM, that sucks!

The wonders of E.F.I..

awesome since it's not the "E.F.I." causing any problems. Don't you have a truck to unload or something?

[IRONHEAD]

Re: 98 Wrangler, No Spark, No Codes...

The details above show that your crank/cam sensing is working fine.

If the ignitor is "built in" to the PCM, that sucks!

The wonders of E.F.I..

awesome since it's not the "E.F.I." causing any problems. Don't you have a truck to unload or something?

nope, but it's still electronic controls..
and the EFI is the reason the spark control is part of the brain(ecu)
working on a cad. engineering project..

[dieselgeek]

Re: 98 Wrangler, No Spark, No Codes...

nope, but it's still electronic controls..
and the EFI is the reason the spark control is part of the brain(ecu)
working on a cad. engineering project..

carbureted 4.0s and iron dukes had "electronic controlled" ignition for YEARS before they became EFI. How about picking a different thread to shit up, and let us help this guy without comments from the Peanut Gallery

[IRONHEAD]

Re: 98 Wrangler, No Spark, No Codes...

nope, but it's still electronic controls..
and the EFI is the reason the spark control is part of the brain(ecu)
working on a cad. engineering project..

carbureted 4.0s and iron dukes had "electronic controlled" ignition for YEARS before they became EFI. How about picking a different thread to shit up, and let us help this guy without comments from the Peanut Gallery

hei module isn't in the computer now is it..
mopars used halls, and don't believe the spark control was in the ecu.. but might be wrong..
peanut gallery,, said sorry..
I'm out the might all knowing d/g has spoken

[SpiderGearsMan]

Re: 98 Wrangler, No Spark, No Codes...

the 4.0 has a hall effect cam sensor in the distributor that also cause no starts
the old hei modules would tell you they are going bad by dying HOT - then restarting cold
used to get bad pickup coils - losing magentic field after about 20 years , you can't argue the reliability of hei in the primitive electronics years
well tested [mag pulse] on all those trans am camaros and L88 corvettes tearing up bridgehampton , mosport, lime rock , elkhart lake and watkins glen