won't start problem

Went on a wheeling trip this weekend and had some problems with the '95 YJ, 2.5L, AX5. The check engine light would not turn on and the fuel pump was not activating. Engine would turn over fine but would not start. Also dash would illuminate, fuel gauge activated, etc. It did start after trying many more times and once started would run perfectly, no misses, no stalling, no hesitation. Any ideas? Thanks, Neale

Reply to
nrs
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CPS?

Reply to
ufatbastehd

Might be but I think the check engine light and fuel pump should still run for a short while with the key on RUN even if the CPS is bad. I don't know, maybe a bad ground or bad computer?

Reply to
nrs

I've had a ground problem with my fuel pump but it did affect the gas gauge, the gas gauge pegs to full when the fuel pump cuts out. I think the check engine light acted as usual. You stated your gas gauge activated so it could be another issue/ground There is a fuel pump ground that's by the e-brake mounting brackets on most YJs.

I havn't found the bad ground yet as my YJ has no grounds on the e brake mounting cable.

Reply to
ufatbastehd

ufatbastehd proclaimed:

Does sound like a bad ground, or possibly just bad battery connect. IF it truly runs after starting, the alternator would appear to be able to pump enough juice to keep voltage up even with a bad ground or cabling

Reply to
Lon

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Thanks for that idea, I hadn't thought about that possibility. I'm still thinking bad ground because the starter works well so maybe it is just the ground to the computer that is bad. I'll try cleaning all ground straps and connections and get a new battery since it may be getting old (was in jeep when I bought it about 1.5 years ago).

Reply to
nrs

nrs proclaimed:

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If you don't know the history of that battery, it never hurts, some of the cheapest cab fare and tow truck charge prevention available.

If you don't already have one, pick up an inexpensive digital volt-ohmmeter. You want a digital, as checking grounds and power cables requires better than 1 tenth volt accuracy. More accurate than using an ohmmeter.

First run your engine so the battery is presumably charged and at operating temperature.

Then turn your engine off.

Turn your headlights on bright for at least 30 seconds, then turn them off.

Wait 5 to 10 minutes.

Pull the negative lead at the battery.

Measure across the battery. Absolute minimum 12.4 volts [this is the open circuit test] Then hook up the negative lead again.

True load test is expensive equipment, but mostly free at any place that sells batteries.

To test current drain with the key off. Pull the key, pull the negative lead. Hook an ammeter set at the very highest scale between the battery post and the negative lead. Reasonable typical drain is 20 milliamps. Turn your meter down slowly to lower scales to check. [Starting at the highest scale helps keep the magic smoke inside the meter where it belongs]

Easiest way to check cables is to measure the voltage across them. Again, start on at least a 12 volt scale at each reading, then turn the scale down so you can easily see a voltage of 1 to 2 tenths of a volt.

Measure from each battery post to the connector at that post. With the engine cranking, you should never see as much as 2 tenths of a volt from each post to its connector.

Measure from the negative post [not the connector] to body ground and then again to engine ground. With the engine cranking, absolute highest reading should be 2 tenths of a volt. Anything higher, you got a bad connect or cable.

Check from positive post [not the connector] down to the starter solenoid. With engine cranking, again, no more than 2 tenths of a volt. If you can reach across the solenoid, measure straight from the battery positive post to the input to the starter while cranking. Again, no more than 2 tenths of a volt.

If you find a higher reading, just move the meter leads until you find the connection with the highest reading, take it apart and clean the snot out of it, put back together and retry.

Lather, rinse, repeat.

Reply to
Lon

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Thanks for the procedure. I'll do this and then report the results. May take me a while...

Reply to
nrs

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Here is an update, positive but not very satisfying. Yesterday I made sure all the fuses were OK and pushed them in firmly. Tried to start and no go. Then I checked the voltages at the relay cavities to see if the battery voltage was present whith the ignition on RUN (and not present with ignition off). It was fine so it looks like the ignition switch is not the problem. I then checked at the computer data link and it had a ground and power from the ignition. I then turned off the ignition and turned it back to RUN and the check engine light came on! I was pretty surprised. I then put the relays back in and it started right up. Since then I have started it about 3 times with no problems and have verified about 20-30 times that the fuel pump runs each time the ignition switch goes to RUN. Also, no relevant codes come up with the on-off-on-off-on method. It seems to be working fine now. What bothers me is that I didn't do anything to fix it and this type of fix tends to unfix later. Could the computer have been reset in some way when checking at the data link?

Reply to
nrs

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Doncha hate that when that happens.

By any chance, was your local weather rather cool and humid when it wouldnt work? I've seen that, in combination with corrosion on contacts, be just the last straw in turning a working contact into a not so working contact. You pound on stuff, you pull wires and put them back... and the problem goes away until the next cool wet spell. In my case it was corrosion inside the ignition switch--which the local service manager claimed "those never fail like that".

Reply to
Lon

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Yes, that was exactly the kind of weather in the area. I live at 1500 feet but when it first failed we were up near 10,500 feet, cold and rainy. When I checked the computer ground at the data link it had a small voltage drop across the connector and the engine block. I'll take that as a sign the ground is a bit bad so I'll be cleaning it this weekend along with all the relay connections. Thanks for your help with this.

Reply to
nrs

The problem came back and I finally took it to the dealership where they confirmed that the problem is the PCM. I'll be looking for a used PCM now. Thanks for all the help.

Reply to
nrs

Reply to
L.W. (Bill) Hughes III

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