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Aversnell
October 15th, 2017, 11:59
Chasing hard starting issue on 96 XJ 4.0 2wd auto with in-tank fuel pressure regulator. Takes multiple cranks, hot or cold. Have already....

Replaced fuel pump and pressure regulator
Replaced tps
Replaced IAC
Cleaned throttle body
Battery, dist. cap, rotor, plugs and wires all replaced 10 months ago.

Ordered an intake air temp. sensor to try next. No CEL during all of this. Just hard starting.

From what Iíve read here, another possible culprit is the CPS. But I have NO other issues... once she starts, she runs and idles smooth and strong. Is it possible for a faulty CPS to cause hard starting and no other symptoms?

Bourne
October 15th, 2017, 12:03
Could also be an injector leaking after shutdown. That won't throw a code. My starting problem was solved by replacing the injectors.

Aversnell
October 15th, 2017, 13:02
Could also be an injector leaking after shutdown. That won't throw a code. My starting problem was solved by replacing the injectors.

Yeah, Iíve thought about that... but if I had a leaky injector, wouldnít I have perforrnance problems beyond hard starting?

old_man
October 15th, 2017, 13:23
Before throwing expensive parts at the problem. Do some troubleshooting. Before starting, cycle the key from off to on several times, allowing the fuel pump to spin up and build fuel pressure.

If it starts quickly with that, then you most likely have a bad back flow valve in the fuel pump. There are tons of threads on here about that and you can insert a one way valve in the line to fix the problem without having to replace the pump.

Aversnell
October 15th, 2017, 13:41
Before throwing expensive parts at the problem. Do some troubleshooting. Before starting, cycle the key from off to on several times, allowing the fuel pump to spin up and build fuel pressure.

If it starts quickly with that, then you most likely have a bad back flow valve in the fuel pump. There are tons of threads on here about that and you can insert a one way valve in the line to fix the problem without having to replace the pump.

Already replaced the in-tank regulator (check valve) and pump (Bosch pump). Regulator part is no longer made for 96 in-tank but used crown model that worked for another poster. Canít do external check valveóreturnless system, I understand thatís a no no.

Cycling the key about 10 times will get a start, but cycling two or three times with foot on pedal works too. Donít want to assume I put faulty parts in the tank yet... hoping to eliminate other possible causes first.

Does anybody know the answer to my question: is bad CPS worth a try?

Tim_MN
October 15th, 2017, 14:44
Diagnose first, then buy parts.

A faulty CPS typically causes random stalling and/or a no-start. The CPS and all the other sensors can be tested. A faulty CPS does not typically cause hard starting. Having the issues occur hot and cold somewhat suggests fuel problems rather than sensor problems.

Test the fuel pressure with the engine running. Leave the tester installed overnight, and check pressure in the morning before attempting to start. Watch the fuel pressure while your helper cranks the starter.

If you have to feather the gas pedal to start, suspect low voltage or interrupted voltage, either/both of which delete the idle settings from the PCM.

Green XJ Jeep
October 15th, 2017, 15:14
If you are having to hold the pedal down double check your tps adjustment

old_man
October 15th, 2017, 16:09
Check the auto shut down relay. It keeps the power to the ecu for a few seconds after the ignition is shut off, allowing it time to reset the TPS to be ready for a restart. If this doesn't happen, you will get the results you describe. If cycling the key several times fixes it, it is not the CPS.

Anak
October 15th, 2017, 16:19
Diagnose first, then buy parts.

A faulty CPS typically causes random stalling and/or a no-start. The CPS and all the other sensors can be tested. A faulty CPS does not typically cause hard starting. Having the issues occur hot and cold somewhat suggests fuel problems rather than sensor problems.

Test the fuel pressure with the engine running. Leave the tester installed overnight, and check pressure in the morning before attempting to start. Watch the fuel pressure while your helper cranks the starter.

If you have to feather the gas pedal to start, suspect low voltage or interrupted voltage, either/both of which delete the idle settings from the PCM.


^^^

This is what I was going to advise.

Finding out what is happening with your fuel pressure is a simple place to start.

Tim_MN
October 15th, 2017, 16:26
If you are having to hold the pedal down double check your tps adjustment

There is no TPS adjustment for OBD-I or OBD-II Cherokees, only for pre 1991 Renix Cherokees.

It could also be the Di-Lithium Crystals, or perhaps even the Flux Capacitor, but using some common sense, and some basic trouble shooting, one should start with simple diagnostics of the most common and the most likely causes of hard starting.

Which is missing, movement of the starter, fuel, or spark ?






.

Dragonslayer
October 15th, 2017, 17:57
Check the MAP Sensor with an Ohm Meter and a vacuum pump (Mity-Vac). There are
websites out there on how to do this.

Aversnell
October 19th, 2017, 16:13
Okay, got a fuel pressure tester. Hereís what I know (again, 96 4.0 auto with in-tank regulator):

Warm engine, key to ON: pressure reads about 52 psi.
Engine running: needle shakes, but center of where itís shaking reads about 55.
Engine off. Pressure starts dropping immediately
After 10 minutes: 35
After 20 minutes: 25

Restarted and let it idle a few minutes. Then shut off and immediately clamped the rubber fuel line between the tank and the filter. Weirdly, pressure dropped off even faster:

10 minutes: 25
20 minutes: 18

I suppose the clamp may not be completely stopping flow, but still this suggests to me that the problem is not in the tank, but elsewhere. I can not see or smell any gas anywhere along the lines where I can see. Does this mean the most likely culprit is leaky injectors? Iím praying everything is okay in the tank, as having already replaced the pump once and the regulator twice, Iím not sure what else to do in there.

Aversnell
October 19th, 2017, 16:32
Check the auto shut down relay. It keeps the power to the ecu for a few seconds after the ignition is shut off, allowing it time to reset the TPS to be ready for a restart. If this doesn't happen, you will get the results you describe. If cycling the key several times fixes it, it is not the CPS.

Swapped the auto shut down relay with the ac clutch relay (ac works) since itís the same part. No change.

Tim_MN
October 19th, 2017, 17:45
With the rubber fuel line clamped, if the pressure falls below 49 psi fairly rapidly then the problem is probably one or more leaky injectors.

Aversnell
October 19th, 2017, 18:55
With the rubber fuel line clamped, if the pressure falls below 49 psi fairly rapidly then the problem is probably one or more leaky injectors.

Thanks. Iím hoping thatís it. Iíll do the injectors this weekend. I already had a set ready to do an upgrade. Fingers crossed. Looks fairly likely that the injectors I have now. are the originals, with 150k on them. Theyíre due.

Aversnell
October 21st, 2017, 13:55
Dud the injector. Jeep starts and runs fine. Don’t know yet about the pressure, and I’m a little worried because the replacement injectors did not work with the clips that came off the old ones, so I didn’t use the clips. We’ll see.

Johnnie Walker
October 22nd, 2017, 12:59
Does your starter sound healthy when it engages?
I had an issue recently where wheb it was cold and/or didn't drive it for a couple of days it would barely crank or not at all.
At first I equated it to the terminals being covered in oil. But after I cleaned it up it didn't take long after that to do the same.
The last time I jumped the starter solenoid with a pry bar, I realizd that there was play in the solenoid housing.
Replaced the starter, and good as new. The old starter was at least 10 years old.
Not to say this is your exact issue, but if your fuel pressure and evefything elses looks good. Consider testing your starter.

Anak
October 23rd, 2017, 20:43
Dud the injector. Jeep starts and runs fine. Donít know yet about the pressure, and Iím a little worried because the replacement injectors did not work with the clips that came off the old ones, so I didnít use the clips. Weíll see.

Are we talking about clips to hold the plugs on the top of the injectors (wiring) or clips to hold the injectors into the fuel rail (and prevent fuel leaks)?