1997 Grand Cherokee ZJ 4.0 206,000 miles
Chasing down a crank - no start/no spark
THE GOOD AND KNOWN:
Battrery-new and good, Interstate 800cca.
Jeep is in great shape, with what appears to be un-touched wiring by a P.O.
Battery cable ends are new, crimp-on, bolted to military terminals. done by me.
All grounds cleaned and good. Alternator cables removed and cleaned.
All fuses checked and good. Never had a blown fuse.
Relays are new and functioning.
All connectors and visible wiring looks good.
Pcm's pull appropriate codes eg. with disconnected MAP / TPS / IAC sensors.
Get no ckp , cmp or any other error codes.
I do have 12v to coil at Key-on and when cranking (ASD relay good).
I get fuel pump. Pulled the FP relay so I don't get gas during many cranking sessions.( plugs are out)
Fuel injectors activate.
Starter draws 139 amps at crank. This is good with the plugs out. New starter
Fuel and volt guages, and all instrument cluster functions work.
Distributor points rotor to #1 (5 oclock) at TDC compression stroke..
My CKP and CMP sensors have 5v/0v triggering on the 5v signal line when hand cranking indicating they are functioning. (CKP sees the 12 reluctor sections) (CMP sees the pulse ring)
Have 2 identical PCM's (406AC). Both act identically.
Now for the problem description: THE BAD:
I have good 5.18v reference at appropriate sensors and at pcm pin 17 at Key-on, HOWEVER--
when I crank with starter the 5v jumps to roughly 10.9v. ( double checked with 2nd DVOM)
Everything I have seen says the 5v ref should remain constant, even at crank.
Spark is being tested at the coil. 6500 Ohms on 12 inch coil wire.
( I have 3 coils, 2 are new, same results from all coils)
When cranking by hand, Key-on, get no spark. However, I do get one lone spark every two revolutions of the crankshaft, always at the same crank position, not TDC ( I marked it on the vibration damper)
Fuel injectors and relays click.
When cranking with starter, I get one, sometimes two sparks but only after key is relaxed back to KO.
It appears these 1-2 sparks are with engine "coasting" (all 6 plugs are out)
Occasionally I will get one lone spark at beginning of a crank session.
I'm thinking either a short to power or ground in wiring harness.
Or - a bad pcm is giving the jump to 10v on 5v signal line when cranking with starter.
(I doubt the PCM possibility - get identical results with second PCM however a slim possibility that both PCM's are identically bad)
A bit of history and possilbly relevant information:
I bought this ZJ 8 years ago. Ran flawlessly, put about 1000 miles on and decided to change oil.
Looking in the oil fill hole, saw LOTS of sludge. Pulled Valve cover, completely sludged up.
Could even see rocker arm impressions in the mostly dried out sludge. May explain the clicking
that came from that area.
Drove it into an old shed, pulled the oil pan and scraped and vacummed out what I could.
Flushed/sprayed solvent thru engine in an attempt to de-sludge it as good as possible.
Pulled it into my garage. decided to replace oil pump, rear main seal and rod bearings. They
needed .001 to get back to clearance spec. 206,000 miles on it. Planned on driving
this ZJ for as long as I could and didn't want to have to remove oil pan again.
Not fun, remove engine mounts, jack engine up a bit to get clearance to remove pan.
Primed oil pump and put distributor back in. Yes, Correctly.
I show oil pressure and hear the lifters draining. ( New oil pump must be working)
Wanted to start it before putting it back together ( radiator, bumpers etc. still off)
This is when I got the No Spark response. Put the project on hold till I had time to focus on it.
Well, now, 8 years later with it stored in house garage (no mice) it was time to get back to it.
Recently retired and now have some time. Spent the last 4 months educating myself on
automotive electronics via forums, videos, and whatever I could find to help me diagnose this
problem. No expert yet but comfortable with meters, power probe, obdII scanner, bore scope. etc.
Lots of new toys to play with.
After various stages of testing, I found this "10v surge at crank on the 5v reference circuit."
Reaching out to a certified mechanic: "I used to see this in the shop and what we used to find was where the main engine wiring harness takes a 90 degree turn at rear of cylinder head - wires would rub and short to ground causing a no start like this -- it is at least worth an inspection."
Maybe when I lifted the engine for oil pan clearance, some harness wires got compromised.
That is the direction I will take but I wanted to reach out to this excellent forum group to
get other ideas and input and maybe help with another persons problem.
Sure would like to get spark so I can drain the old gas and put it all back together and drive it.
This is my first thread post, ever, on any forum. Hope I'm doing it right.
Thanks for reading, got a little long but I felt it necessary to include all relavent information.
Chasing down a crank - no start/no spark
THE GOOD AND KNOWN:
Battrery-new and good, Interstate 800cca.
Jeep is in great shape, with what appears to be un-touched wiring by a P.O.
Battery cable ends are new, crimp-on, bolted to military terminals. done by me.
All grounds cleaned and good. Alternator cables removed and cleaned.
All fuses checked and good. Never had a blown fuse.
Relays are new and functioning.
All connectors and visible wiring looks good.
Pcm's pull appropriate codes eg. with disconnected MAP / TPS / IAC sensors.
Get no ckp , cmp or any other error codes.
I do have 12v to coil at Key-on and when cranking (ASD relay good).
I get fuel pump. Pulled the FP relay so I don't get gas during many cranking sessions.( plugs are out)
Fuel injectors activate.
Starter draws 139 amps at crank. This is good with the plugs out. New starter
Fuel and volt guages, and all instrument cluster functions work.
Distributor points rotor to #1 (5 oclock) at TDC compression stroke..
My CKP and CMP sensors have 5v/0v triggering on the 5v signal line when hand cranking indicating they are functioning. (CKP sees the 12 reluctor sections) (CMP sees the pulse ring)
Have 2 identical PCM's (406AC). Both act identically.
Now for the problem description: THE BAD:
I have good 5.18v reference at appropriate sensors and at pcm pin 17 at Key-on, HOWEVER--
when I crank with starter the 5v jumps to roughly 10.9v. ( double checked with 2nd DVOM)
Everything I have seen says the 5v ref should remain constant, even at crank.
Spark is being tested at the coil. 6500 Ohms on 12 inch coil wire.
( I have 3 coils, 2 are new, same results from all coils)
When cranking by hand, Key-on, get no spark. However, I do get one lone spark every two revolutions of the crankshaft, always at the same crank position, not TDC ( I marked it on the vibration damper)
Fuel injectors and relays click.
When cranking with starter, I get one, sometimes two sparks but only after key is relaxed back to KO.
It appears these 1-2 sparks are with engine "coasting" (all 6 plugs are out)
Occasionally I will get one lone spark at beginning of a crank session.
I'm thinking either a short to power or ground in wiring harness.
Or - a bad pcm is giving the jump to 10v on 5v signal line when cranking with starter.
(I doubt the PCM possibility - get identical results with second PCM however a slim possibility that both PCM's are identically bad)
A bit of history and possilbly relevant information:
I bought this ZJ 8 years ago. Ran flawlessly, put about 1000 miles on and decided to change oil.
Looking in the oil fill hole, saw LOTS of sludge. Pulled Valve cover, completely sludged up.
Could even see rocker arm impressions in the mostly dried out sludge. May explain the clicking
that came from that area.
Drove it into an old shed, pulled the oil pan and scraped and vacummed out what I could.
Flushed/sprayed solvent thru engine in an attempt to de-sludge it as good as possible.
Pulled it into my garage. decided to replace oil pump, rear main seal and rod bearings. They
needed .001 to get back to clearance spec. 206,000 miles on it. Planned on driving
this ZJ for as long as I could and didn't want to have to remove oil pan again.
Not fun, remove engine mounts, jack engine up a bit to get clearance to remove pan.
Primed oil pump and put distributor back in. Yes, Correctly.
I show oil pressure and hear the lifters draining. ( New oil pump must be working)
Wanted to start it before putting it back together ( radiator, bumpers etc. still off)
This is when I got the No Spark response. Put the project on hold till I had time to focus on it.
Well, now, 8 years later with it stored in house garage (no mice) it was time to get back to it.
Recently retired and now have some time. Spent the last 4 months educating myself on
automotive electronics via forums, videos, and whatever I could find to help me diagnose this
problem. No expert yet but comfortable with meters, power probe, obdII scanner, bore scope. etc.
Lots of new toys to play with.
After various stages of testing, I found this "10v surge at crank on the 5v reference circuit."
Reaching out to a certified mechanic: "I used to see this in the shop and what we used to find was where the main engine wiring harness takes a 90 degree turn at rear of cylinder head - wires would rub and short to ground causing a no start like this -- it is at least worth an inspection."
Maybe when I lifted the engine for oil pan clearance, some harness wires got compromised.
That is the direction I will take but I wanted to reach out to this excellent forum group to
get other ideas and input and maybe help with another persons problem.
Sure would like to get spark so I can drain the old gas and put it all back together and drive it.
This is my first thread post, ever, on any forum. Hope I'm doing it right.
Thanks for reading, got a little long but I felt it necessary to include all relavent information.
