post #1 of Old 02-12-2015, 09:11 AM Thread Starter
cowteets
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97 ZJ 5.2L cold engine no start

Any insight guys?

5.2L ZJ running in to starting problems this winter.

If temp was below 40 degrees, it took 5-10min of turning key to accessory mode, letting comp cycle and fuel rails prime. Eventually it would start. Once the engine warms up, I can cut it off and start it up again no problem. It is only when engine is completely cold that I run in to this issue.
Now its not starting at all without starter fluid. If its warm enough outside (yesterday it was 45) and I spray a few squirts in to intake, it will stay running after a few tries. I let it run for 30min. Shut if off, started right back up etc. Even after a few hours. It will start up fine until engine is completely cold.

This morning its 28 out and no dice after 10min of trying and spraying starter fluid. Will rev but then die.

There is no test port on the rail for fuel pressure test. The FSM states that some builds do not have one. However, because it will start and stay running under the right conditions, it does not seem to be fuel pump related. Something tells me it has to do with the PCM and the startup protocols it runs though. Would a bad coolant temp sensor do this? Crankshaft Position Sensor? Intake Manifold Air Temp Sensor? It clearly has to do with temperature.

I cleaned the Throttle Position Sensor, bought new spark plugs (3 of the old plugs on right side had thick sludge around the nut, but not below the thread. Need new valve cover gaskets maybe? thats besides the point!

Here's what FSM says about startup procedure, which makes me think its PCM-related:

ENGINE START-UP MODE
This is an Open Loop mode. The following actions occur when the starter motor is engaged. The power train control module (PCM) receives inputs from:
Battery Voltage
Engine Coolant Temperature Sensor
Crankshaft Position Sensor
Intake Manifold Air Temperature Sensor
Manifold absolute pressure (MAP) sensor
Throtle Position Sensor (TPS)
Starter Motor Relay
Camshaft Position Sensor Signal
The PCM monitors the crankshaft position sensor. If the PCM does not receive a crankshaft position sensor signal within 3 seconds of cranking the engine, it will shut down the fuel injection system
The fuel pump is activated by the PCM through the fuel pump relay.
Voltage is applied to the fuel injectors with the ASD realty via the PCM. The PCM will then control the injection sequence and injector pulse width by turning the ground circuit to each individual injector on and off.

The PCM determines the proper ignition timing according to input received from the crankshaft position sensor

ENGINE WARM-UP MODE
This is an Open Loop mode. During engine warm-up, the power train control module (PCM) receives inputs from:
Battery voltage
Crankshaft position sensor
engine coolant temperature sensor
intake manifold air temperature sensor
manifold absolute pressure (MAP) sensor
throttle position sensor (TPS)
Camshaft position sensor signal (in the distributor)
Park/Neutral switch
Air condition select signal
Air condition request signal

Based on these inputs the following occurs:
Voltage is applied to the fuel injectors with the ASD relay via the PCM. The PCM will then control the injection sequence and injector pulse width by turning the ground circuit to each individual injector on and off
The PCM adjusts engine idle speed through the idle air control (IAC) motor and adjusts ignition timing
The PCM operates the a/c compressor clutch through the clutch realay
When the engine has reached operating temperature, the PCM will begin monitoring the O2S sensor input. The system will then leave warm-up mode and go into closed loop operation

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post #2 of Old 02-13-2015, 06:14 AM
ZeeJay1997
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It's most likely the fuel pump.

When it will not start do the gauges and warning lights work okay? Does the check engine light cycle for 3 seconds when the key is moved to the on position?

try using a heat pad around the PCM over night. A common "oh, my back" pad will work.
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post #3 of Old 02-14-2015, 09:23 AM Thread Starter
cowteets
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Why would it be the fuel Pump when it seems temperature related? If it were the fuel pump, that would suggest the fuel pump is only necessary when starting the vehicle. Is this the case?
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post #4 of Old 02-14-2015, 11:10 AM
ZeeJay1997
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because electric motors have temperature related issues too. not only does the engine warm up, so does the fuel pump. when it is not wanting to run, get under there and whack the lowest part of the tank with a rubber hammer and see if it starts picking up.
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post #5 of Old 02-14-2015, 11:13 AM Thread Starter
cowteets
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Hmmm but it stays running after it starts, even when engine is cold. Yhe problem is getting it to start, not keeping it running. Make sense? Do those factors still point you to fuel pump? Appreciate the insight!
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post #6 of Old 02-14-2015, 11:27 AM
ZeeJay1997
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the multiple key cycle thing is a classic symptom of a failing fuel pump.

a failing PCM can mimic this symptom. this is more common on the earlier models, but the laters models are not immune. it could be bad caps in the pcm. this is why you need to heat the pcm up (without running the pump) and see if it still does it.
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post #7 of Old 02-14-2015, 11:40 AM
a70eliminator
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I had a similar issue when my battery was low from the cold, problem was it took so much current to crank the cold engine that it caused a voltage drop that would set off the anti theft circuit, in anti theft the engine will start but die withing a second or two, you can maybe even get in a quick rev before it cuts the ignition. A new battery solved it.
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post #8 of Old 02-15-2015, 12:47 PM Thread Starter
cowteets
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great insight guys. i'll run a blow dryer on the PCM for 10min and see if that helps.
then i'll try jumping it from a running vehicle and see if the voltage diff has any impact.
Will also do some voltage testing. Im great with mechanics, but terrible w/ electric so was trying to avoid this

Fuel pump test questions:
How do you test the fuel pressure if there is no test valve on the rails? Do I have to pull the line off of the rail and test from that? Also, should I be able to hear the fuel pump if I lay under the tank while someone turns the key on to accessory? Is that clicking and movement in the dash when the accessory is turned on, the pump priming the rails?

Thanks again
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post #9 of Old 02-15-2015, 01:04 PM
ZeeJay1997
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Quote:
Originally Posted by cowteets View Post
How do you test the fuel pressure if there is no test valve on the rails? Do I have to pull the line off of the rail and test from that?
yes, depressurize rail, clean the fitting, squeeze tabs on bottom and pull straight up on the clip. then you have to figure out how to hook a gauge up

Quote:
Originally Posted by cowteets View Post
Also, should I be able to hear the fuel pump if I lay under the tank while someone turns the key on to accessory?
yes, but turn the switch to ON


Quote:
Originally Posted by cowteets View Post
Is that clicking and movement in the dash when the accessory is turned on, the pump priming the rails?
not sure what you're hearing, but you the rails priming should not make noise
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post #10 of Old 02-15-2015, 02:58 PM
wkbear
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Quote:
Originally Posted by ZeeJay1997 View Post
not sure what you're hearing, but you the rails priming should not make noise
I know I need a fuel pump, but when mine primes after sitting for a day or over night it makes a groaning noise. Almost like muffled cracking or pooping. Cranks fine after it's warm and runs fine otherwise. Not asking for advice, just giving input.

1995 Grand Cherokee Ltd., 5.2, 249, stock (for now)
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post #11 of Old 02-15-2015, 03:22 PM
sskilla
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While you are messing with your PCM you could pull it out and check/clean the connections and use some dielectric grease on the pins.

Also sometimes that pcm starts to sag messing with the connections. I got a big fat zip tie and made sure it was squeezed into place real tight.

Zeejay1997 mentioned bad caps in the pcm. If you dig in that deep there is a write-up floating around showing you how to replace them.

That said, it sounds like a failing cps to me.

Good luck with the hunt man!

'95 ZJ: 5.2 v8 / 231 Tcase / 46RH
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post #12 of Old 02-15-2015, 05:24 PM
ZeeJay1997
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Quote:
Originally Posted by wkbear View Post
I know I need a fuel pump, but when mine primes after sitting for a day or over night it makes a groaning noise. Almost like muffled cracking or pooping. Cranks fine after it's warm and runs fine otherwise. Not asking for advice, just giving input.
There you go OP, does your noise sound like that? The 4.0 doesnt make any noise even if it's empty. I suppose having two rails can generate the noise described.
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post #13 of Old 02-15-2015, 05:40 PM Thread Starter
cowteets
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The noise happens twice when switched to accessory on: first time immediately when the key is turned and then about 5 seconds later when the middle console display says my coolant sensor is bad and does that series of beeps.

The sound is like a whirring, then a couple of clicks/knocks each time. Almost like its testing av vent ports. It sounds like it's coming from under the top dash under the hood close to the fire wall. It's done it for forever. I just assumed it was priming the rails. You guys are saying that noise iisn't normal? Thanks for the chatter this is helpful for me to mull through.
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post #14 of Old 02-15-2015, 06:30 PM
ZeeJay1997
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Quote:
Originally Posted by cowteets View Post
The noise happens twice when switched to accessory on:
accessory position is when the top of the key is moved towards the driver.

on is the first position when the top of the key is moved towards the dash

the coolant sensor bad message has nothing to do with the problem you have. ignore it... for now.

get someone to move the key while you check the rail for the noise. it's sounding more like a bad fuel pump.
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post #15 of Old 02-15-2015, 08:41 PM Thread Starter
cowteets
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Sorry, not accessory, that what I mean, the "on" position. . Its always made the noise I'm referencing, as long as I can remember. I'll get under the car when I can and see if I can hear the fuel pump making some noise.

hoping to narrow this down. If it had a flippin test port on the rail then I'd have had the fuel pump question solved a week ago.
ill be tinkering this week, will post with some new info and hopefully resolution.

Thanks for insight guys
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