Ignition problem

[FritzTKatt]

Back to ignition problems for me... yeah I've got a mess on my hands that all got to get cleaned up. The guys that have been here for a while probably remember when I messed up the truck last year, now I'm finally fixing it.

Had the broken clutch pushrod, fixed. Now the starter interlock works... No fuel pump, fixed. Needed a relay, the old one popped but wasn't a strong enough connection I guess. Easy fix. When I got it back the spark plugs weren't gapped right, and the plug wires were mixed up, easy fix.

Now here's the more complex problem: cranks, but no fire. Has fuel at the rail, has fuel come out the exhaust. So I'll assume the injectors work. The plug wires were new a year ago. They have all of 20 miles on them. Plugs are questionable but I inspected them and gapped to .054.

I have 12v to the hot wire at the coil pack with KOEO, and 0v at the 3 ground wires (as it should be). I pulled the wire off the coil for the middle drive plug (front/left on the coil) and held it close to the coil. It gave a spark then fired that cylinder. But it won't fire that cylinder with it plugged in... I'm lost.

Thinking that I need to get the coil pack tested as well as the ICM. I had replaced the PCM already.

 

[RonD]

Having all 3 coils in a coil pack fail would be rare, usual issue when a coil pack is failing is misfiring, not a no start.

An ignition coil generates a spark by cutting it's power, thats what the points did on the old system, when points were closed coil got power(was grounded), when points opened power(the ground) was cut and primary coil field collapsed, this sends out a spark on secondary coil(to spark plug wire).
Newer systems just use a transistor to cut the ground, so no moving parts to wear out.

On the '94 the spark is initiated by the CKP(crank position) sensor sending a pulse to the EDIS-6 module, the pulse de-notes TDC for the engine, so EDIS module knows when #1 piston is at the top of its stroke, power or exhaust stroke doesn't matter since this type of system sends spark on both strokes, a waste spark system.
Without CKP sensor pulse EDIS module doesn't know crank/engine is even turning so there would be no spark started.

On my '94 4.0l the EDIS module is located on the front of the radiator support drivers side, hard to see but looking up from under the vehicle you can see it.

CKP sensor wires run to this module and the 3 Grounds for the coil come from this module, it is also connected to the computer(PCM) for advanced timing settings and injector timing, but EDIS modules are autonomous, they can run the spark on the engine without PCM input.

EDIS module is powered by the EEC relay closing, same as coil, fuel injectors, and Fuel pump relay.

If you have an old spark plug I would test if it sparks when cranking engine, just testing the wire can be misleading since there is no "load"(spark plug) on the system.
And not just one spark, it needs to spark many times, to be sure it isn't just a "build up" spark, each one revolution of the crank = 1 spark at any chosen wire

 

[FritzTKatt]

A few of the wires did read way too much resistance, since they had been stretched to reach the wrong plugs (stupid mechanic), so I had to replace them, put new plugs in while I was at it. Verified ICM is good by checking resistance of 5-6 pins and resistance between pin 8 and all the other ones matching an ICM from the box. Verified coil to be good by checking it against a random one that a guy gave me, and a brand new one at the store (all tested the same).

CKP wires don't have ridiculous resistance but seems high (forget the numbers), I probed them at the ICM and used the pig tail at the CKP sensor. The CKP sensor is definitely new (mechanic put it on), so I'll call it good since I don't have a spec to check it against, and it's new. Only thing left I can think of is to check for a voltage pulse on the 5 or 6 pin at the ICM (probe the wire) while cranking the motor? And if that doesn't exist at at least one of them, then I suppose it's time to rebuild that section of the wiring harness?

 

[FritzTKatt]

Update: the 3 wires (yellow red/black/white) from the ICM to coil have continuity, the ICM ground (pin 9) is good. I can't readily check pin 4 (ground at the pcm), and don't know if pin 7 (shielding for CKP) is supposed to ground.

Still need to test for pulse on pin 5/6 while cranking, but need a buddy for that. I do have continuity of the wires and (I'd have to go check again, tbh) an amount of voltage with KOEO (it made me think that the wiring was good).

I just don't know what can really be wrong anymore. All of the system seems to work fine less the check for CKP pulse which I honestly think is there. What should I do if there is pulse but still no fire? And if the pulse doesn't exist, and I test the CKP to a new one or whatever, and the CKP is good, then what?

 

[FritzTKatt]

Major update. I finally had it. I couldn't stare at this thing for any longer.

Pulled the harness, and sure as stink on chevy, the ckp wires are messed up. You might ask "well fritz, how messed up are they?" To that I'd say, some idiot that did my motor swap, cut the wires, and nipped them off at the sensor plug. Twisted new wire in there, and taped it all over. So it would match the rest. Maybe I'll post pictures later.

So now, off to Napa for a $15 plug and grab some extra odd and ends. I'll fix this with some real crimp connections, new wire, new shielding, heat shrink, the whole mess. Continuity existed, but not enough to send full signal.

 

[FritzTKatt]

Rebuilt it... again... waiting for light and the liquid tape to dry. Instead of 5-6 ohms over the circuit it's 0-1 ohms. In all of my genius I forgot to grab a upper intake gasket. Can you permatex an upper intake? I have lots of red, black, copper, and maybe some grey. I can get whole caulk tubes of red at work.

 

[RonD]

Yes, you can "make a gasket" for the upper intake

 

[FritzTKatt]

Would you recommend spacers like a washer to mimic a gasket? Or just do a small bead to seal?

 

[RonD]

Just the "sealer", and just a little of it, you are only compensating for rough surfaces.

 

[FritzTKatt]

Sweet. I already made the smart choice to stuff papertowel in the intake ports so no junk gets in there. Eventually I'll end up pulling it again and put real gaskets.

The connectors that napa sells fit the ckp, and injectors, they're about $15 just so everyone knows. These have a metal spring clip instead of stupid plastic ears, actually designed to be removed.