Starts Drives Quits

[Locked98GC]

1995 Jeep Cherokee, 4.0, auto, 4x4, Sport. About 8 months ago I did a 4ga upgrade to the positive and negative cables. All of the grounds are clean and tight. I have replaced 2 crankshaft position sensors. I replace the fuel pump, strainer and a new fuel filter. I get 32 psi on the fuel rail at idle and 41 with the vacuum pulled off the fuel pressure regulator. Same readings as the old one (Bosch, hey, got a spare now).

I can not get out of the Jeep quick enough to open the hood, disconnect the connector and throw a multimeter on it, about 5-10 seconds, to check the CPS. The 2nd one might actually be good since I can't get a faulty reading.

The Jeep will idle in the driveway without a hitch. I can jump on the bumper and rock it and it still runs. When I drive it about 2-3 blocks it stops running completely, either going around a corner or driving in a straight line. Out on the highway I get about half to one mile before it dies. After about 10-15 seconds it will start right back up and off I go for a block or 2 and it will die again. It does this if the engine is hot or cold.

I have checked the coil hot and cold with about the same resistances and passes.

I did rebuild the neutral safety switch while I was replacing the first CPS. It would start in all gears and no reverse lights. It still starts in all gears but now it has reverse lights. Something fishy there, but the NSS has been out since I bought it 4 years ago.

So, at the moment I'm stumped. I've also wiggled all the wires I can see while it's in the driveway idling or revving it up and it won't die. Seems like it will only die while it is moving. The 2 replaced CPS are Napa Echlin. I know go get a Mopar one.

 

[MoFo]

How many different threads are you going to start for this same problem before you go to the dealer and buy that OEM CPS? You could have bought 3 of them for what you spent on that "spare" fuel pump. When the computer does not see the right signal from the CPS (at start or during run), it will disable the fuel pump.

 

[Locked98GC]

One is for the CPS itself. One for the fuel pump replacement, and this one for the whole problem. In 4 years I have 175 posts mostly helping people. If you don't want to read my posts then stop. This isn't Jeep Forum or Pirate 4X4.

No, I could not have bought 3 CPS with the $100 I spent on the fuel pump.

 

[8Mud]

Does the MIL come on at any time? Does the MIL come on before it quits or after it quits? Have you done a key test to get the stored codes?

Is it possible the motor dies when you let your foot off the gas pedal? Or does it die with the pedal depressed? Don't jump to conclusions answering this one, be sure before you answer.

 

[Locked98GC]

Does the MIL come on at any time?
Does the MIL come on before it quits or after it quits?

Have you done a key test to get the stored codes? Yes 12, I've had the battery cable off though. There was an 11 on the first (original) CPS. The 2 new ones no 11 code.

Is it possible the motor dies when you let your foot off the gas pedal? Yes, like when coming to a stop. This last trip if I kept the revs up while stopping, going around corners and driving with the brakes keeping me at 25 it would not die. It did this on the prior test drive too so I took the throttle body off then the IAC and cleaned both up. Pintle was pretty cruddy but still the same problem.

Or does it die with the pedal depressed?

Don't jump to conclusions answering this one, be sure before you answer.
I will check the others tomorrow.

 

[Locked98GC]

Things done today.
I checked all of the connectors and applied dielectric grease including computer connector.
Got lots of exhaust, so system is not clogged.
Cleaned TB and IAC.
Checked intake, no clogs.
Checked engine wiring harness for nicks, cuts, pinches, pins seated right, etc.
Checked grounds and resistance. From the negative battery the the A/C compressor 1.0 ohm.
Did a light load check on charging system. Lights on high and A/C on, fan high. 14.02V with or without a load.

 

[8Mud]

The only air you get into the motor with your foot off the pedal is through the IAC. If it is sticky or faulty the motor can stall for lack of air. Been my experience you need about 1/8 pedal to keep the motor going if the IAC is stuck shut.

Before you run down and buy a new IAC, about half the time the problem is dirt and about half the time the problem is a charging or battery problem. More often than not (actually most every time) the IAC is still good.

Try spraying some oil into the IAC opening with the motor running, while you work the throttle a little. When I remove the IAC I always let a few drops of synthetic oil run down behind the piston into the piston drive gears. It sometimes gets gritty in the drive gears, the grease gets thick. If all else fails you can try spraying/flushing out the drive (behind the piston) with contact spray, as a last resort. I'm always a little hesitant to do this, fearing I may do more damage than good, I'd hate to force some grit deeper into the gears or motor drive.

Personally I'm a little careful where I smear dielectric grease.

 

[Locked98GC]

Items checked to day.

Does the MIL come on at any time? No
Does the MIL come on before it quits or after it quits? No

Have you done a key test to get the stored codes? Yes 12, I've had the battery cable off though. There was an 11 on the first (original) CPS. The 2 new ones no 11 code.

Is it possible the motor dies when you let your foot off the gas pedal? Yes, like when coming to a stop. This last trip if I kept the revs up while stopping, going around corners and driving with the brakes keeping me at 25 it would not die. It did this on the prior test drive too so I took the throttle body off then the IAC and cleaned both up. Pintle was pretty cruddy but still the same problem.

Or does it die with the pedal depressed? Yes, if it didn't quit at the stop sign, sometimes it will die while leaving from a stop. It also chugs/runs very roughly about 1 out if 5 times. I can hold the gas pedal down and it will try to keep running but will not go back to normal running. I have to turn the key off and it will start right back up. This happens when gas pedal is at rest and pressed.

Oiled the IAC
Looked at all vacuum hoses/lines. 22 hg at the manifold. The line that runs to the vacuum reservoir there is a "T" fitting, checked vacuum and it was at 12. About 5" from the "T" the line was deteriorated with many holes. After I pulled the battery and holder assy it was deteriorated almost to the vacuum reservoir. I have it capped at the "T" for now and pulling 17 hg at idle and 21 just above idle. Drove it like that and still dies/chugs.

 

[Locked98GC]

Also checked the TPS. The FSM says with the throttle plate closed, the center wire back probed, and key on, it should have greater than 0.200 (200mV). I have 0.800. With the throttle plate wide open, it should be less than 4.8V, I have 3.8V. It falls in the parameters and has a smooth reading between the 2 parameters.

 

[SanDiegoXJ]

I'd guess cps.

I'll look and see if I have my old one around here. It's no good, but if it makes your jeep run like mine used to, that would be the issue. =)

 

[Demonoid369]

Have you checked the pick up coil? Sounds like what I was having troubles with, looks like the pick up coil needs to be replaced about the same time as the CPS. Seems like the pick up coil is sorta rare but if you've covered everything else, I'd check there

 

[RedHeep]

When it dies and won't start, is it no fuel or is it no spark?

 

[8Mud]

When it dies and won't start, is it no fuel or is it no spark?

This is always a good strategy for troubleshooting "No Starts" or "sudden death syndrome" .

The orange wire going to the CPS, the cam position sensor and your speed sensor (in the transfer case) are all the same power source. Low voltage to the CPS, should be around 8 volts in the 95, will cause what you describe. The problem is it can be a partial short, one partially bad sensor that sucks down the sensor supply voltage to the other two. The first sensor that goes out of range throws a code and it may not be the faulty sensor.

Easy test, turn the key to run and check the voltage on the orange wire with the connectors still connected. The last time mine did what you describe I had around 3 volts on that wire, I unplugged sensors until the voltage went back up.

As a side note, when my sensor was shorting out the Check Engine Light wouldn't light with the key in the run position. It should come on as a test lamp function. If it doesn't come on when you turn the key to the run position, you can unplug sensors (either the CPS, Cam position sensor or speed senor on the 95) and the lamp should come back on (if the bulb is good) as soon as you unplug the bad sensor. This works only if it is the sensor, a wiring fault (partial short, like a wire melting down on the exhaust or rubbing through someplace) may affect (turn off) the Check Engine Light, but unplugging any sensor isn't going to help any. I've heard a shorted sensor may also cut the power to some gauges, those connected to the PCM. I doubt this is a sure thing, it may depend on the severity of the short or other factors.

 

[RedHeep]

This is always a good strategy for troubleshooting "No Starts" or "sudden death syndrome" .

Sometimes when we're troubleshooting, we skip to page 10 and start replacing parts without thinking about the basics. Air, fuel, spark. The systems in the car are specifically tailored to provide all 3 of those for combustion, but if you don't know which one is lacking, you don't know what system to troubleshoot.

A lot of people (myself included) have spent a lot of money replacing things because we didn't start at the beginning and figure out what branch of the troubleshooting tree to climb on. Doesn't matter if we're talking about jeeps, lawn mowers or turbine aircraft.

 

[Locked98GC]

It will run all day in the driveway revving it up, sitting at idle, sitting back end up, front end up, shaking it, or bouncing it.

It just cuts out while driving. I've looked for shorted wires, I will look again later.

Replaced the IAC today.
Repaired all the vacuum hoses. Pulling 20 hg at all spots.

Pulling CPS tomorrow and getting a Mopar one.

 

[Locked98GC]

Checked the voltage on the orange power source for all three, it was 7.44V.

Before I did that, I thought it has to be a short somewhere. Started checking the grounds again, and there she was just barely touching the other wire on the ground ring. Dang it's fixed.....

I still have the problem, but I did fix the ground.

 

[Locked98GC]

San Diego don't have a MOPAR CPS. You just can't pick one up from the dealer, they all had to order. I don't like the idea of ordering it on line and not working but the Stealerships want $121 for it. Dang, I thought the Corvette tax was high. $56 on the web for a MOPAR one.

 

[Locked98GC]

Found a Mopar CPS (P/N 56026882) at Rancho Jeep on Balboa Ave. They had a couple of them @$80.60. Put it in the Jeep this morning and actually got to go further than a couple of miles. Went for about a 20-25 mile drive and it ran well. Took it to get gas and still ran (and no leaks).

Should I have listened and got the Mopar CPS? Yes (and no). I found a lot of minor discrepancies and a few major ones that got repaired correctly. Crossing the fingers it doesn't start again.