nhopa

Update: Yesterday morning the Jeep started up normal. I did some shopping with several stops then drove home. No problems. Around 11 AM I measured the TPS voltage with ignition on but engine not running. I measured .96 Volt to 4.0 Volts from closed to fully open position. Started the engine without problem. The throttle opened slightly and I measured 1.0 Volt. I think the normal TPS range is .2 Volt to less than 5.0 volts. So the measurements were definitively within the proper range, perhaps the .96 Volt being a little bit too high. Unfortunately the outside air temperature was only about 98-100 F. Today when the temperature is expected to go up to
about 100 F I will repeat the test while heating the TPS with a hair dryer to see if it will drop out.

DFlintstone

I didn't read the thread....My 90 is different but the IAC, IAT, TPS, almost everything is often as warm as 114* there. When you shut off a 210* engine, most everything on it is gonna get pretty toasty, day in, day out. What I mean is that that stuff is used to being hot. Coils are known to get grumpy, hot. All those wingdings and tight clearance.....Not sure how long it would take to cool one down if it were hot, as a test. (it amounts to a pretty sizable chunk of metal). 20 mins, 1/2 hr? Just a thought.

nhopa

Hi DFlinstone and others follow this thread:
Yesterday we had only 100 F so I set up for the test of the TPS. At closed position of the throttle the voltage was .98 V. I started the engine, it run well and the TPS voltage was 1.00 V. Next I turned on my heat gun at low setting and heated up the TPS and the throttle body with no effect on the running engine. Next I heated the computer, again with no effect. I must wait until our temperature goes back to about 110 F in a couple of days.
Some other observations: Couple of days ago when I could not start the engine I checked that there was fuel pressure in the header by pushing on the Schrader valve and seeing gas gushing out. I could also hear the fuel pump running. With my OBD I now get a P0303 code, no.3 cylinder misfiring. I probably picked up this code the other day when the engine was just cranking. Currently the engine light is not on.
So the question remaining is: what shouts down or prevents the engine to start when the outside temperature is around 110 F?
I would say that so far I have eliminated the AIT sensor, the computer, the TPS and the fuel system as a potential problem. What remains is the ignition system. It is difficult to check for spark with the coil packs over the spark plugs when the engine just cranks but wont start. It is obvious that the engine will not shut down when the computer senses a misfire in one of the cylinders. May be one of the relays associated with ignition drops out a higher temperatures? Any suggestions?


Reading some of the comments on the internet from various sources one would compelled to start changing out every component one by one. But this is not right, there must be just one reason for this problem. I can't believe that no one on this or other Jeep forums have not experienced this problem. There are so many Jeeps running around in Arizona. On this forum there should be a matrix that lists the various problems and indicates the proven fix for that problem.


My next car will be a 1968 Barracuda with a 318 V8. No computers, no BS, it got over 20 miles per gallon on the highways. With my Cuda I always passed the emission test in New Jersey, which was one of the strictest in the Nation.

Jeep Driver

Did you swap out the fuel pump relay as I suggested

nhopa

Hi Jeep Driver:
I have not changed out the relay yet. As I indicated previously when the engine would not start just crank, the fuel pump was running and I had pressure in the fuel header. I think the problem is with the absence of sparks at high temperatures, except I do not know how to test for that.
This morning I ran some errands, temperature in the high 80s, no problem with engine.

Jeep Driver

Swap it with the AC relay.

Will cost you nothing.

nhopa

Hi Jeep Driver:
I did switch the fuel pump relay with the AC relay. Now I just have to wait until temperature goes above 110 F in the next couple of days. In the mean time, any suggestions on how to check if the coil packs are getting voltage when the engine just cranks?

CFreeman

Your stalling issue is a replica to the same issue I have/had. When my jeep stalled, we tried to bypass the relay. We found there was no current at the relay, so that did not work. It almost like there is something with heat that causes the computer to shut down all, cutting off all electrical to the ignition; like there is a short in a common ground.
I would clean the Throttle body and the TPS, it should be part of normal maintenace anyhow. Another issue, I would consider the CPS.
I wanted to add, I have not had a problem since I did the replacement of the sensors I mentioned earlier. I still have one final test, I want to take the jeep off-road on a steep climb (that heats it up quickly). I will keep you posted.

nhopa

Hi CFreeman: In an earlier post I indicated that in one of the tests I have heated both the TPS and then the CPS with a heat gun way beyond a 114 degree F outside temperature without any failure or engine stoppage. Today we are going to have over 110 F today so I can see if the swap of the relays suggested by Jeep Driver did the trick.
The question remains if the engine will not start just cranks, how can I check for sparks with the coil pack and the cover over them?

Cvail

You can check for spark this way.

nhopa

Hi Cvail and other members watching:
Thank you for the information. I drove the Jeep this morning and everything was fine. Parked the Jeep in a garage with 98 F. At 3 PM I drove the Jeep for about 10 minutes (6 miles) and the engine died. Air temperature was 111 F. I waited 5 minutes and the engine started so I drove another 5 minutes and parked the Jeep for about 30 minutes, then tried to start the engine but it would not run just crank. So what is wrong with my Jeep?

Turbo X_J

Any codes yet? This Bermuda triangle stuff is how a lot of vehicles end up on CL.

nhopa

Hi Turbo X J and Cvail:
Although, I do not have the engine light on, I do get code P0303 on my code reader. I watched the video and I found one on how to test the coil pack, so I will do that test and also check how many miles do I have on the spark plugs.

nhopa

Update:
After a hour of struggle I managed to remove the coil pack by cutting the four wires connecting it to the harness. This should not be that difficult. I ran some test on the coil pack. I measured the resistance between 1-6, 2-5 and 3-4 coils. The average reading was 1,680 Ohms. Ambient temperature was 105 F. Next I heated the 3 coils with a heat gun way beyond what would be an ambient temperature of 114 F. I the measured the resistances and I got about 1,730 Ohms at each test points. Conclusion is that the coil pack works as designed. Next I will try forcefully remove the connector from the coil pack, solder long leads between the cut wires, wait for ambient to go to about 110 F and see if I get sparks. I assume the four wires are ground and three signal to the coils. I do not think they are high voltage but are the coming from the computer? In that case the problem would be with the computer. Any thoughts?

nhopa

Update.
Added a 6 inch pig tail between the plug and the four cut wires. Reassembled the coil pack and the engine runs just fine. The question is that the four wires, one common ground and the three signal wires do they go to the computer direct or there is some other "gismo" between them? If there is a direct connection than the computer is having problem at higher temperatures. If I will have to replace the computer are there any suggestions from forum members, that is what is the best way to proceed?