Replaced everything...what am I overlooking?

[deeallen]

Anybody please help! I have a 89 Jeep Cherokee inline6 4.0L. Jeep wouldn't start, put on a new fuel filter and it started. 2 days later wouldn't start so I had the fuel pump replaced, started ran great. Next morning, Jeep wouldn't start. Getting no spark into coil, tested coil, that was good. Tested ICM, that was bad. Replaced that still no spark. Battery was pretty low, had to jump a few times so I just replaced that. Also the ballace resister, just 'cuz its a cheap part and I replaced before and started right up.

Still nothing. So I've been online trying to figure this out. I replaced the CPS. Jeep starts! Then dies after about 5 sec. Thought is might be fuel pressure, so replaced the fuel pressure regulator. Still starts then dies. So I start thinking maybe sensors. Checked TPS, bad so I replaced. Still the same thing. Replaced the relay that controls automatic shut-off. Starts then dies after 7-8 sec. Then replaced the Oil pressure switch, same thing.

The idle air sensor was next, nothing. Check the air flow system. I have oil in my air filter and my grommet on my crankshaft ventilation system is shot, oil leaks from it. So those lines got cleaned out. After all of these problems I thought the ECS, the computer didn't work. I'd have to say 8 sec is the max the old Jeep will stay runnin.

ANYBODY PLEASE HELP! ANY SUGGESTIONS???!!!

[capt. apathy]

check your map sensor and the vacuum lines that run to it. the lines are hard plastic with rubber ends. if the end that plugs in undre the map sensor comes off it will pop right back up into possition so that it apears to be on, check it with your hands.

I spent hours trying to get mine to run right only to find that damn vacuum line had slipped off, very frustrating but at least it didn't cost anything to fix.

[deeallen]

Today I sprayed carb. cleaner into throttle body and as long as I spray this into throttle body it stays running. I was told this is a fuel problem and I probably got a bad pump when it was replaced. Any new ideas?
All the lines have been checked and cleaned (air does go through), the MAP sensor is attached, what exactly does the MAP sensor do?

[capt. apathy]

the MAP(manifold absolute pressure, IIRC) sensor sends readings of the pressure (or lack of it, I'd assume) in your intake manifold to the ECU so it can use this info to determine proper fuel mixture and the like.

have taken off and cleaned the Idle-air-stepper-motor? (next to the TPS) last summer mine got very gummed up and really screwed up the idle(as I understand it the plunger goes in and out and fine-tunes the amount of air provided at idle), the old oil and tar like residue was causing the crome plunger to get stuck and when the motor tried to retract it.

I pulled mine off and cleaned it, and the port in the throttle body it mounts in, with an old toothbrush and some wd-40, smoothed the idle right out.

[Po Pilot]

CPS - crankshaft position sensor back on the bell housing. Has caused many a jeep not to start or intermittent start.

[jbbinf]

Don't know if the problem has been fixed yet...and I appreciate the notes on the MAP sensor maintenance. Have you run a complete check on your wires, specifically your battery cables? I had a similar problem with idle and no start. Ended up replacing both battery cables, they were toast after 160k miles. No further issues!

[capt. apathy]

that last post reminded me of anther thing to check. the conections of all of your sensors. I've had a lot of problems with corosion or loose conections to the sensors. I've had the diagnostic computer telling me my CTS and TPS where bad, then after unplugging and plugging them back in it ran fine.

so it wouldn't hurt to check over your sensors, make sure there is no corrosion, and adjsut the pins so they fit tight. saved me a lot of trouble. my gas milage went up a couple mpg after cleaning the conection to the CTS, seems it was sending a bad signal due to the bad conection and the ECU had the jeep in constant warm-up settings.

[Js808]

I can tell you NOT to look for a crank shaft position sensor. These are only used on distributor-less ignition systems. You have a distributor for sure, so don't worry with that.
You have obviously replaced just about every sensor you have on the Jeep. You need to run some tests to make sure of some things. Just to be sure, I would run a compression test. Compare the compression of all of the cylinders. If they vary by 10-20 psi..you've got a problem. After that, perform a cylinder-leak-down test. This will tell you if everything is sealing well internally. Then perform a fuel pressure test. Once you have ruled out any problems with pressure, then look into bad connections. Most electrical problems are caused by poor grounds, so get out your meter and check for any breaks. If you still haven't found anything abnormal, check vacuum lines. Like someone posted earlier, these rubber lines cotarize after years of heat and they become brittle. You need to run these test to determine where, specifically, the problem is so you can isolate it and fix it.

[Dale Aeppli]

Originally Posted by Js808

I can tell you NOT to look for a crank shaft position sensor. These are only used on distributor-less ignition systems. You have a distributor for sure, so don't worry with that.
You have obviously replaced just about every sensor you have on the Jeep. You need to run some tests to make sure of some things. Just to be sure, I would run a compression test. Compare the compression of all of the cylinders. If they vary by 10-20 psi..you've got a problem. After that, perform a cylinder-leak-down test. This will tell you if everything is sealing well internally. Then perform a fuel pressure test. Once you have ruled out any problems with pressure, then look into bad connections. Most electrical problems are caused by poor grounds, so get out your meter and check for any breaks. If you still haven't found anything abnormal, check vacuum lines. Like someone posted earlier, these rubber lines cotarize after years of heat and they become brittle. You need to run these test to determine where, specifically, the problem is so you can isolate it and fix it.

UP DATE IF YOU HAVE A DISTRIBUTOR YOU HAVE A CRANKSHAFT POSITION SENSOR. DON'T KNOW WHAT YEAR BUT MY FIRST WAS ON A 86 2.5 DALE

[capt. apathy]

my 89 4.0 had a CPS and a distributor

[Js808]

You may have had a sensor, but it wasn't a crankshaft positioning sensor. Most distributor type electronic ignition systems have either a magnetic pickup or "Hall effect" sensor that generates a signal as the distributor shaft rotates. On distributor less ignition systems, the trigger signal is generated by a Hall effect or magnetic crankshaft position sensor (and cam position sensor in many applications). The trigger signal goes to the ignition module, which switches the ignition coil on and off to fire the spark plugs. If the pickup or Hall effect switch is not producing a signal, or if the ignition module is not processing the signal, the coil won't fire.

[capt. apathy]

yes , it was a CPS. it was a CPS in the book, was a CPS on the diagnostic computer, and when I called the parts house and ordered a new crankshaft possitioning sensor, they sold me one, I removed one that looked just like it, and put the new one on in the same spot.

it is a magnetic pick-up only instead of being on the distributor it's on the flywheel with the sensor on the bell-housing. with the fly-wheel being attached to the crank shaft this sensor lets the ECU know the position of the crankshaft as the magnet passes the sensor.

[Js808]

This must be a Chrylser thing...that's just really odd. I see no need for a CPS if you have a distributor.
Thanks for the info.

[Dale Aeppli]

Originally Posted by Js808

This must be a Chrylser thing...that's just really odd. I see no need for a CPS if you have a distributor.
Thanks for the info.

HI LIKE THE CAPT. SAID THERE IS A CRANKSHAFT POSITION SENSOR THE HALLEFFECT SENSOR YOU ARE REFFERING TO IS MOUNTED IN DISTRIBUTOR. IF YOU DISCONNECT THE CRANK SENSOR YOU WILL GET NO SPARK FROM THE COIL . THE VEHICLE WILL RESTART AFTER IT SHUTS DOWN IF CRANKSHAFT POSITION SENSOR IS GOING IF THE CAMSHAFT POSITION SENSOR GOES BAD THE VEHICLE WILL NOT START TILL YOU CHANGE THE CAMSHAFT POSITION SENSOR IN THE DISRTIBUTOR WHEN JEEP STARTED USEING CRANKSHAFT SENSORS THEY WERE CALL VEHICLE SPEED SENSOR THAT WAS WHAT THEY CALLED IT IN 1986 DALE

[debb718]

change engine and transmission to chevy