'93 GCherokee 6 Hard Start

D did pass the time by typing:

That's close. 15,340 vs 18,000 Keep in mind that your vehicle may be warmer than air temp if it's sitting in the sun or in a garage.

A quick way to check that sensor is to unscrew it, then nuke yourself a cup of water. Measure the sensor and watch the change as you dunk it in the water. It should go quickly down to 640-720. If it doesn't budge then it's dead.

I doubt it is dead though. Usually when that happens they just show as an open circuit, but it is possible. Anyhow, that would be the next thing I'd check.

.. another thought.. Have you checked the rotor and cap for any cracks/traces/burns?

L.W. (ßill) Hughes III did pass the time by typing:

No kidding, the tach connection on the old GM HEI unit was handy. But loosing the points system sure doesn't make me cry. :)

Only thing I can do now is clamp onto the #1 plug wire and with the new cars you don't even have a plug wire. :/

Anyhoo.. Just got back from the local dealership where they re-did the CV boot. Guess the tech that fixed it last August didn't get the band on exactly right so it was blowing grease. Dealership didn't give me one bit of grief and they even cleaned the mess off the suspension. They must have a new manager, last time was a royal pain.

Got to test drive a few new vehicles including the 2004 Dodge Durango with a Hemi. :D ... help ... That is a big SUV but did it ride nice. Plastic bumpers though, but what else is new.

That and this pic of a tailpipe from the lot. Dang thing was big enough to put a DrPepper can into.

Since you are swinging the leads of that DVOM around, find a convenient place to tap into the CPS circuit, and see if you are getting anything . If your DVOM has HZ capability, you should pick up some reading while cranking. The exact reading isn't important, just that there is something going on...

More later...let me read a little.

Jerry

1. Auto Shutdown Relay (ASR) provides power to fuel pump, coil, fuel injectors, and O2 sensor heaters. If you have fuel pressure, don't worry about the ASR.

1. If PCM does not sense input from the crankshaft position sensor, PCM will deactivate Automatic Shutdown (ASD) and fuel pump relay, interrupting voltage to fuel pump, fuel injectors, and ignition coil, (no start condition).

2. For what it is worth.... I have seen several different makes of vehicles exhibit a condition of no start when humid or cold, and it was caused by secondary ignition components (spark plug wires most common). When there is high humidity and you have substandard ignition parts, the path to ground becomes much more convenient via a cracked wire or cracked coil due to the extra conductivity of the air.

Go and check that CPS on the HZ range or the AC volts range, and see if anything is going on with it. You can condemn it before digging it out.

Jerry

The service manual states to test the CPS with the DRB II diagnostic scan tool. Lacking that, the quick and dirty test is to place an ohmmeter across terminals B and C. Near the rear of the intake manifold, disconnect sensor pigtail harness connector from main wiring harness. Looking into the CPS connector, with the clip up, you will see a notch on the right side. In that position, the terminals read A, B, C left to right. Ohmmeter should be set to 1K-to-10K scale for this test. The meter reading should be open (no resistance). Replace sensor if a low resistance is indicated. All taken from the official

Dick

No fancy DVOM is needed, all that's needed is a plain old analog VOM that can read low AC voltages, and most do.

Jerry

-- Jerry Bransford To email, remove 'me' from my email address KC6TAY, PP-ASEL See the Geezer Jeep at

Great information Jerry. Thanks for both of your posts. I'm getting excited to go out and work on her in the morning again. I made some comments below.

I do have good fuel pressure. There's the ASR eliminated. Great!

Since I do get good fuel pressure, and I will check it again in the morning, this tells me the PCM is hearing from the CPS then.

If you've missed the whole thread, this no start problem has been steadily getting worse over the last month when it started to get colder. Does that info sway your thoughts in any way? At about 60K miles, the car died in the road with no warning. Turned out to be the coil. Will a coil gradually degrade to cause starting problems but run well once started?

Yeah, a coil can gradually degrade, particularly if a crack is developing. Definitely check that.

As far as the fuel pressure goes, be careful: you should have fuel pressure with key on, and while cranking, but ASD will shut it down if there is no CPS signal. So, you may have fuel pressure when you turn the key on, but no continuation of fuel pressure, and no spark as well, due to ASD deactivation, with a root cause of CPS failure. Sound confusing? Just think like the box does. If you were the computer, you would turn on the fuel pump at key on, then shut it off if you had no crankshaft pulse. It doesn't know the engine is turning if that CPS isn't doing its thing.

Hope you have a fruitful morning.

Jerry

Thanks again Jerry. Might have something here. Check me out. The coil. I get .9 to 1.0 ohm between the spade terminals. Seems ok. I get infinity or open between either of the spade connectors to the tower connector where the coild connects from the distributor. Got it setting here on my desk. I also get open between the tower connector and the housing or ground. Sound like a bad coil to you?

Based on my memory of old, round coils, which is fading faster these days, there shouldn't be any continuity between the primary (spade terminals) and secondary (coil wire terminal) sides of the coil. The spark is caused by the collapse of the primary field, and if it were shorted to the secondary side, there would be no field to collapse.

I say the coil is good, at least in the electrical sense.

Jerry

interrupting

Nevermind. I've had this coil on my desk staring at me, waitin gfor my son to take me to the car store. Now I get a 20,300 ohm reading between the tower connector and the primary spade connectors which would indicate it's okay. The CPS checked okay by the way with infinity between pins B & C. Think I'll take the coil to the car store anyway and have them look at it. Am I back to square one? Oh, the fuel pressure was good at key on, it held at 32 PSI through cranking. It also held for over an hour now without dropping appreciably.

interrupting

Sheesh, I would probably gamble the 15 bucks or whatever and put a new coil in. Cheap insurance. The next thing that I would look for would be an actual spark, and/or an actual injector pulse. Put a test light across any injector connector, it should flash as you crank. DVOM won't pick it up, it is too fast.

Jerry

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D did pass the time by typing:

Book says 11,300 - 15,300

You can do a spark check on the Jeep. Put the coil back, and disconnect the primary wire off the distributor. Hold it about 1/2" from the block and have someone crank the engine. You should get a steady arc. Needless to say, watch your fingers, that puppy bites hard.

That's good for fuel pressure, if your jeep was starting then stalling out or refusing to accelerate then it might be fuel flow. But I don't think that is your problem.

While your checking sensors, check the TPS (throttle position sensor) it's on the throttle body across from the linkage

Thanks Doug, Took the coil in and it tested at 14,500 on the secondary. Another thing they had me check was for the 8 volts at the CPS connection. I get 0 vdc between the black/white and black/blue wire. 0.18 vdc between the black/blue and the other wire. SInce I don't have 8 vdc happening there, it points to the wiring between the CPS and the PCM, or to the PCM itself right? I have the PCM on my desk now. Anything I can check on it? Thanks all. Denny

appreciably.

D did pass the time by typing:

The PCM feeds 8V to the Crankshaft Position Sensor and the Camshaft Position Sensor. The wire should be White with a Black Stripe

While you have the PCM out.

Disconnect the sensor in the distributor and check between Pin 7 on the PCM harness and Pin 1 (the White/black wire) on the CPS connector. There should be near zero resistance. Also check between either of those pins and the white/black wire going to the distributor. Those form a T splice that might have gotten corroded.

Not rilly. To check the PCM requires a scantool.

Hold on a sec.. lemme scan something for you.

I'll post back when it's done.

Should be readable though.

Thanks Doug, I'm really hoping all this mess comes down to hidden corrosion. I pushed this old girl into the garage, so when I catch my breath, I'll check the wires between the PCM and the CPS, then between the two to the dist.

I drove my wife's '93 Cherokee home one night...it was running just fine. The next morning I went out to start it and nothing. After many checks and replacing the crank sensor, it turned out to be the PCM. First disconnect the coil and probe the terminals of the harness with a test light connected to a good ground while cranking the motor. One of the terminals should light the light. If you have 12v to one terminal on the coil harness while cranking, check the other terminal with the test light hooked to 12v battery voltage. If the light flashes while you're cranking the engine, replace the coil. If you have no light, first test the wire between the coil and the PCM for an open. If the wire is ok, replace the PCM.

-- Old Crow '82 Shovelhead FLT 92" 'Pearl' '95 Jeep YJ Rio Grande ASE Certified Master Auto Tech + L1 TOMKAT, BS#133, SENS, MAMBM, DOF#51