94 Jeep ZJ 5.2 intermittent stall after start - JeepForum.com
 
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post #1 of 9 Old 09-22-2017, 04:31 PM Thread Starter
speedbrake
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94 Jeep ZJ 5.2 intermittent Stall after Starting

After Jeep sits overnight or a few days, it sometimes fails to start. Sometimes. If engine’s been running recently I get the intermittent No Start a lot less. When I’ve been able to replicate the No Start, here’s how it goes: Turn key On. CEL comes on, then goes out. I hear the fuel pump run briefly. Fuel pressure goes to 35 psi at the fuel rail. Turn key to Start. Engine fires up, goes vroom! Fuel pressure immediately falls to 5 psi or less. Engine sputters at sub-idle and quickly dies. No significant codes thrown. All I get is 12 (battery’s been recently disconnected) and 55 (code finished signal). I’m thinking fuel pump. But before I throw a $200 Bosch at the problem and do the ‘drop the tank’ dance, I want to see what the experts think. The thing that makes me question the fuel pump being the culprit is, when this happens, it ONLY happens at Start. Never while driving. Never while loading up the engine with A/C, or sudden acceleration. Never at idle, stopping, uphill, downhill, varying amounts of gas in tank, etc. Just Start. Once I get it running, it runs until I turn the key off.

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post #2 of 9 Old 09-22-2017, 04:32 PM Thread Starter
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When the problem started a few weeks ago, I found that with key On, fuel pressure initially went to 35 psi, then would bleed off to zero in the space of a few minutes. Put new O-rings on the fuel pressure regulator, old ones were hard/inflexible, and the ‘pressure bleed off’ problem went away. It now passes the FSM fuel press regulator check with flying colors. But the original problem of No Start has still not been solved.

Last edited by speedbrake; 09-24-2017 at 09:22 AM. Reason: Nobody has responded yet.
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post #3 of 9 Old 09-22-2017, 04:33 PM Thread Starter
speedbrake
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I’ve been doing the Dirty Dozen. I do get the CEL briefly on with key ON (normal, I believe). Grounds have been located, cleaned, made shiny. Found the ‘bad caps’ write up for 93-94 ZJ PCM. Symptoms sounded similar, and I fixed two TVs by changing caps, so I replaced those 3 notorious capacitors. Didn’t help. IAC’s been cleaned. Cleaned PDC relays, battery cables, alternator connections. Resting battery voltage is 12.6V. Swapped fuel pump relay with ABS relay. They both work. Did the Kolak ignition kit. It’s got a brand new MSD coil, distr cap, rotor, plugs and wires. So that's where I'm at. Could some experts please weigh in and tell me where my problem may lie or some more troubleshooting I could do to isolate it. Thanks!

Last edited by speedbrake; 09-24-2017 at 09:24 AM. Reason: To try to get some responses :-)
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post #4 of 9 Old 09-25-2017, 08:48 AM Thread Starter
speedbrake
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Anyone? It's been three days since I posted this. 70+ people have read it. Nobody has responded. Could really use some advice. Please.
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post #5 of 9 Old 09-25-2017, 09:15 AM
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If the pressure is dropping while the fuel pump has voltage then the fuel pump is bad. The voltage can be measured at the connector by the tank.

When I replaced mine w/ the Bosch pump, I disconnected the fill hose, fed in a siphon tube, drained the fuel into gasoline cans to make handling the tank manageable.

The inexpensive fuel pumps are garbage. I had two fail. The Bosch is a strong performer.


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post #6 of 9 Old 09-25-2017, 01:17 PM
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When you cleaned your grounds/alternator connections did you also clean the ground under the alternator above/behind the coil on front of head? That should be your PCM ground with black/tan stripe wire on the eyelet.

Believe after it's been running for the day I'd let the engine cool down then connect your fuel pressure tester to it. Start it back up then just leave the fuel pressure tester connected. Then when you start it back up after sitting overnight see if you aren't getting full fuel pressure causing a no-start condition. Fuel pump then would be suspect.

Also on a no-start condition you may want to pull the coil wire and see if you can get it to arch to the distributor cap port. Also put the coil wire back in and see if pulling a plug wire to see if there's spark there? If coil wire sparks but plug wire doesn't then there a problem within cap/rotor.

The main purpose of the above test is checking to see if the crank sensor which controls spark it working correctly. I've had bad crank sensors drive me nuts where they cause a no-spark condition on first start-up while others wanted to fail after reaching normal operating temps.

While the crank sensor connector on your 94 5.2 sure isn't easy to get to there's a crank sensor resistance test in my signature which is pretty reliable. Any resistance at all between B&C and it's bad. Good luck.

96 4.0 ZJ Laredo, 2004 4.7L WJ Limited, 96 4.0 XJ (son's)


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post #7 of 9 Old 09-25-2017, 08:16 PM Thread Starter
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Thank you, gentlemen, for the responses. Uniblurb, Yes, cleaned ALL the contacts on the alternator and above/behind the coil bracket. Also the grounds on the pax side outboard of the battery. Used a wire brush and stainless steel little dremel wire wheel on the wire eyelets, threads, nuts. All grounds looked new and shiny when put back together.

Looks like my next step should be: try to replicate the No Start with fuel pressure tester (which I've done) but this time simultaneously use a multimeter to check fuel pump voltage at the tank. I'll report back on that. If I can keep it No Starting, then I'll do the two spark checks you described.

I've read about the crankshaft position sensor in a bunch of threads. Even found it. As you know, it's a bear to even touch, let alone replace. The wire connector for it was a little easier to get to so I did the crankshaft position sensor resistance test from the FSM. But I'm confused about what it says. FSM says "Ohmmeter should be set to 1K-10K scale for this test. The meter reading should be open (no resistance). Replace sensor if a low resistance is indicated." Can you clarify the "open (no resistance)" part of? It seems like those two things are opposites. To me, "no resistance" means a reading of zero. To me ,"open" means infinite resistance. No resistance means that current can flow through that item very easily. i.e. if you touch the metal leads of the ohmmeter together, it shows 0.000 because there is no resistance between the two. But if I put both ohmmeter leads on a piece of rubber (not a conductor), the meter will show "0L". In other words, 'out of limit' or in this case infinite resistance. So which do they mean by "open (no resistance)"? Do they mean a reading of zero? Or do they mean a reading of 0L? FWIW, on my CKS, when I did the resistance test mine showed "0L" between terminals B & C.
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post #8 of 9 Old 09-25-2017, 10:23 PM
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The pass condition of open, no resistance, means infinite resistance, or OL on your meter.

Low resistance doesn't have to mean zero ohms. With the FSM limits as-described I would be very suspicious of a part that measures less than 100kOhms.

My experience is that lowering the rear of the transmission / transfer case creates enough room to reach the CPS for replacement. (Remove the muffler, transfer case linkage and disconnect the transmission cross member.)





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post #9 of 9 Old 09-26-2017, 01:15 AM
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Quote:
Originally Posted by speedbrake View Post
Thank you, gentlemen, for the responses. Uniblurb, Yes, cleaned ALL the contacts on the alternator and above/behind the coil bracket. Also the grounds on the pax side outboard of the battery. Used a wire brush and stainless steel little dremel wire wheel on the wire eyelets, threads, nuts. All grounds looked new and shiny when put back together.

Looks like my next step should be: try to replicate the No Start with fuel pressure tester (which I've done) but this time simultaneously use a multimeter to check fuel pump voltage at the tank. I'll report back on that. If I can keep it No Starting, then I'll do the two spark checks you described.

I've read about the crankshaft position sensor in a bunch of threads. Even found it. As you know, it's a bear to even touch, let alone replace. The wire connector for it was a little easier to get to so I did the crankshaft position sensor resistance test from the FSM. But I'm confused about what it says. FSM says "Ohmmeter should be set to 1K-10K scale for this test. The meter reading should be open (no resistance). Replace sensor if a low resistance is indicated." Can you clarify the "open (no resistance)" part of? It seems like those two things are opposites. To me, "no resistance" means a reading of zero. To me ,"open" means infinite resistance. No resistance means that current can flow through that item very easily. i.e. if you touch the metal leads of the ohmmeter together, it shows 0.000 because there is no resistance between the two. But if I put both ohmmeter leads on a piece of rubber (not a conductor), the meter will show "0L". In other words, 'out of limit' or in this case infinite resistance. So which do they mean by "open (no resistance)"? Do they mean a reading of zero? Or do they mean a reading of 0L? FWIW, on my CKS, when I did the resistance test mine showed "0L" between terminals B & C.
Rather than getting into a technical discussion on electronic terms I wrote my crank sensor test wording in that post in layman's terms to be more easily understood. And as you know what it says on your ohm meter setting readout can differ from meter to meter. And many meters don't have an 'OL' reading like on a Fluke.

That's the reason in the first paragraph of that test I said the readings between B&C should be "open", the same as if the meter probes weren't touching anything.

Quote:
Originally Posted by Uniblurb View Post
Agree on checking the crank sensor with a multimeter on the disconnected female connector/plug to the sensor itself. With the meter set to one of the lowest ohm settings, and locking tab on the connector up, make sure you place the black probe on the middle B pin (ground cavity) and red probe on the right C pin (power). The reading should be "open", same as if the probes weren't touching anything, and any resistance at all indicates you have a bad crank sensor.
You're more than welcome to write-up your own crank sensor test while explaining infinite resistance for those trying to figure out how to use the ohm setting on their meter. Good luck.

PS. below is even a better crank sensor test where you're checking for crank sensor signal. Pull the fuel pump relay and remove the whole coil wire altogether since you're turning the engine over by hand. Note the 93-95 crank sensor uses 8V of power rather than 5V for the 96-98. This is for a no-spark no-start condition only.

http://troubleshootmyvehicle.com/chr...-sensor-test-1

96 4.0 ZJ Laredo, 2004 4.7L WJ Limited, 96 4.0 XJ (son's)


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