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Unread 02-08-2014, 07:13 PM   #1
Boothe
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Another YJ 4.0 No Start Problem

I started up my 93 YJ (4.0L, auto trans) the other morning to go to work and it was running "funny." Up to this point it has always run flawlessly. The outside air temperature was around 1 degree F. It idled poorly, so I had to give it a little gas to keep the RPM up for warm up. I wrote it off to the cold, although it's never done this even at subzero temps before. So I waited about a minute and a half and when I tried to take off it acted like it wanted to die. I revved it up a little and let it sit for another minute or so. I tried to take off and it stalled out again, but I threw it in neutral and it didn't die. I repeated this a third time and it died. When I restarted it and tried to take off it died completely hasn't restarted since.

I immediately suspected water in the fuel and a frozen filter, so I changed the fuel filter. No water, no ice. I put a gauge on the rail and when I turned on the key, fuel pressure came up to 31 PSI immediately. Even after 10 minutes was still holding above 25 PSI. When I pulled a spark plug it was damp and smelled like gas. No problem there.

I checked the spark with a screwdriver in number 4 wire gapped off ground while my wife cranked it over. It had a spark, but it appeared weak and intermittent. So I repeated the process at the coil wire. The spark would jump a quarter inch, but was yellow with only a faint blue core. So I replaced the distributor cap, rotor, plug wires and coil. I checked, cleaned and gapped the plugs a bit tight to .034" (they were all burnt back to >.040", it had been about 5 years since I checked them). I picked up a real spark gap tester and checked the spark at the number 4 plug wire again. It looks a lot better, still some yellow, but a good spark at the plug and seems to fire consistently. Still no start.

I pulled the codes with the CEL (does this thing even have a diagnostic connector?) and it only showed 12, 33 & 55. No smoking gun there that I could see. Even though the symptoms don't match what I've read here for the all too common ECU / PCM capacitor failure, I pulled the PCM and inspected the caps anyway. They don't appear bulged or otherwise compromised. Now it's true that the electrolyte may have dried out and that wouldn't be visible. But this was a sudden hard failure, not the usual long start time, no CEL, no fuel pump issue. Although I intend to replace the caps (with high end mil-spec tantalum, not the standard aluminum) as a PM, I don't believe that's the issue. Comments?

So, I put a DMM on the stator / pick up coil / cam position sensor connector and all the pins appear to be open with respect to each other. I read on another thread here that I should see somewhere between 400 - 800 ohms between a couple of the pins (I checked between all three). Can anyone confirm that? I'm only working with a Haynes manual and reading through previous posts on this site, but I see a factory service manual in my future. But I went ahead and ordered a rebuilt distributor (it should be in tomorrow). We're in the middle of ice & snow season here and I really would like to get the old girl back on the road ASAP. Any assistance would be greatly appreciated.

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Unread 02-08-2014, 11:11 PM   #2
The_Goob
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Ill give you a bump It seems you have done anything I could have mentioned.
and here is a decent online manual, just select yj in the drop down. its for a 93
http://www.jeep4x4center.com/knowled...rce=cj#service
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Unread 02-09-2014, 07:29 AM   #3
toddcleveland
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Try the crankshaft position sensor. I had the same symptoms and replacing this worked. Cheap part, easy to install, and likely in stock.
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Unread 02-09-2014, 09:16 AM   #4
Boothe
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Goob - Thanks for the link to that online factory service manual. I'm not surprised it's on the Morris site; I just never thought to look. Duh. Now to just find a DRB II cheap...
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Unread 02-09-2014, 09:21 AM   #5
Boothe
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toddcleveland - I wondered about the Crankshaft Position Sensor too. It seems to be a real problem on the XJ's. I had read that the 2.5L had one, but I wasn't sure about the 4.0L (and didn't feel like crawling under the Jeep in the cold to try to find it if it wasn't there). Based on what I read in the on-line manual The Goob pointed me to, it does indeed have one. And that sensor failing would be consistent with the no start condition I experienced and have read about with the XJ's. Thanks for the tip, I'll check it / replace it as needed.

Last edited by Boothe; 02-09-2014 at 09:55 AM..
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Unread 02-09-2014, 11:08 AM   #6
94squareeyes
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Sounds like you have good spark and fuel. I would check to see if it has good compression next. Check the oil to see if its contaminated with coolant. Could be a bad head gasket
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Unread 02-09-2014, 02:37 PM   #7
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CPS- replace it. There is a test for them but they can test good and still be bad. Ask me how I know.

Use only a Mopar sensor.
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Unread 02-09-2014, 07:44 PM   #8
Boothe
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Quote:
Originally Posted by 94squareeyes View Post
Sounds like you have good spark and fuel. I would check to see if it has good compression next. Check the oil to see if its contaminated with coolant. Could be a bad head gasket
I pulled the dipstick and the oil is clear, no signs of coolant. I also pulled the radiator cap and the coolant shows no signs of oil. Since I had just driven her the day before and the old gal ran flawlessly. There has been no excessive steam out the exhaust, no coolant consumption and no performance issues; so head gasket failure is highly unlikely.
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Unread 02-09-2014, 08:00 PM   #9
Boothe
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Quote:
Originally Posted by Why J? View Post
CPS- replace it. There is a test for them but they can test good and still be bad. Ask me how I know.

Use only a Mopar sensor.
I went ahead and picked up a crank position sensor today when I went in to get the reman distributor. I don't have time to wait around for the Mopar part so I bought the Duralast from A.Z. with a lifetime warranty. I know, I know; Auto Zone parts are reputed to be substandard. But I've always had good success with the ones that carry a lifetime warranty. Let's face it, if they were really that bad, A.Z. would have gone under from the cost of replacing them. And one more thing, the CPS I'm replacing is the Mopar original.

Based on what I've read over at the XJ side, the OEM CPS is probably the most failure prone component on the vehicle! Worse yet, when I checked over at Moparpartsonline, you can't even pull up anything earlier than '95 (i.e. Chrysler wants us to throw our old YJ's away and buy a new Jeep). Now, I'm not saying that the Duralast part is any better than the OEM part, it probably isn't. But based on others' reports of the original equipment's high failure rate, I'm not sure how it could be much worse. Just sayin'...
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Unread 02-16-2014, 11:51 PM   #10
Boothe
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Status update: During a visual inspection, I found the crankshaft position sensor cable laying on the no. 6 header tube. The wire loom was completely melted and the signal leads looked burnt. However, when I checked live data with an Autoxray EZ Scan 6000, it displayed 128 RPM during cranking / no start. Since RPM data comes from the crankshaft position sensor, it was obviously still functional. But since the cable was charred, I decided to replace it anyway. The crankshaft position sensor I purchased from Autozone was the wrong part. The one on their website, as well as their in store computer, shows the part for an XJ not a YJ. So I went to Oreilly and picked up the right Borg Warner part (made in Mexico of course). Installing it made no difference; the Jeep still won't start. I did make sure to zip tie the signal lead to the throttle cable to be sure that it didn't' fall back down on the header.

I did notice that throttle position sensor did not seem to respond (it just stayed on 0.8V) as I watched live data on the scanner. So I back probed the connector and turned the key on. The TPS has a blue wire (BLU) which is gnd or signal common, an orange wire (position signal from TPS) and a black / white wire(5.0 V supply). Supply to the TPS was 5.003 VDC. When I moved the throttle body butterfly through its range BLU to ORG read 0.631 to 3.653 VDC (0.821 ohms – 2.639 ohms when powered down). The FSM calls for approx.1 to 4 volts. I don't know if 400 mV low is really a problem, but I'm guessing it's not until someone corrects me.

At this point, as much as I hate to throw parts at a problem, I went ahead and installed a rebuilt distributor too, since the original cam position sensor showed open between all three pins on the connector. I made sure I put it back in the same orientation as the original (even though that doesn't matter since the PCM sets the timing based on crank position). The new distributor didn't change a thing either. So just to be sure (even though I've checked previously) that it wasn't a fuel issue, I poured a couple of ounces of raw gasoline down the throttle body. Same results; cranks and cranks with no start. I ran out of time today, but intend to resume troubleshooting tomorrow. Does anyone have any suggestions?
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Unread 02-17-2014, 12:14 AM   #11
Bigev
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Fuel pressure seems low, I would expect it to jump to 40-55 when you turn the key on, and pump at 45 minimum.


I have run into issues where injectors are clogged, it happened to be a rusting out gas tank in an old ford with dual tanks.
(I'd hate to lead you in the wrong direction... just giving my thoughts.)
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Unread 02-17-2014, 06:38 AM   #12
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Fuel pressure should be 31-39 PSI. It does seem like a fuel issue. Being that it slowly quit running and you have spark, but it may be a sensor issue as well.

Have you checked all the fuses?

The CPS you purchased may be bad, get a Mopar one, store brand have a reputation for being bad out of the box, be aware that a CPS can test good and still be bad. You seem to say that you may have a weak spark? You may be failing to fire under compression.

Also check the CKP (crank position sensor) spec of 200 ohms + or - 75 between terminals A and B.

Also spray in some starting fluid and see if see will start.
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Unread 02-17-2014, 08:34 AM   #13
Boothe
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Why J? - I get a decent spark now that I changed the coil, cap and wires (but I was getting a spark before, it just looked weak to me). Obviously I have no way of knowing what it's doing under compression, just what the spark gap tester shows. And I did pour about a half ounce (or less) of fresh gas directly into the throttle body yesterday (I was out of starting fluid, but will pick some up today) and it didn't even try to fire when it turned over. So I have my doubts about it being a fuel related issue. Plus after you attempt to start it a couple of times, the spark plugs are visibly damp and smell like gas. I am inclined to believe that 31 PSI on the rail is a bit low and it is an aging fuel pump. But I have my doubts about it not starting from lack of fuel based on what I did yesterday, 31 PSI on the rail and relatively new injectors. But I'll try ether just eliminate that possibility.

The original crank position sensor, even though the wires were burnt, is not shorted and does show live RPM data on an Autoxray 6000. Since the FSM says the PCM receives RPM data from the crank position sensor to determine ignition timing, I have to assume that's working as well. Otherwise there would be no data to display. Cranking RPM was 128. I did notice that the OEM crank position sensor had a much stronger internal magnet than the Borg Warner does.

The way it died didn't seem fuel related either. I know how an engine responds due to lack of fuel and this acted more like the timing was severely retarded. I've had that happen on older vehicles both after servicing a conventional distributor and when the hold down bolt came loose. You give it gas, the engine revs, but has no power and dies when you put it under load. It did this the morning it died. What's more you could smell gas.

What seems odd to me is that it hasn't stored any code other than 33. I'm going to put the scanner back on it today and see if the live TPS signal changes with throttle position. It did with my meter on it, but did not change when viewed with the scanner in response to pressing the gas pedal. Perhaps it's a bad connection to the PCM. I'm going through the FSM in more depth today to determine which sensors can give you a no start condition and go from there.

Last edited by Boothe; 02-17-2014 at 09:19 AM..
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Unread 02-17-2014, 09:14 AM   #14
Why J?
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TPS should show up on the scanner when actuating the pedal. IF no signal is present and you give it gas the timing will not advance. And can also give you a no start problem.

I had a Cherokee that the TPS tested good but would get no signal to the ECU, found that if I pressed lightly on the connector it would work. Replaced connector and all was well. This is something you should be able to test for using your scanner.

Next on my list after that would be testing the pins on the ECU.
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Unread 02-17-2014, 09:14 AM   #15
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You are definitely ok on the the CPS. You loose spark when its bad. Your fuel pressure is fine. 31 psi is perfect. You need to get some new plugs. 5 year old plugs....its time to replace them anyways. Check spark to each plug. If you have spark at each plug and it still isnt cranking over then you have a timing issue. You replaced the distributor but did you check to make sure your timing marks all lined up? Are you getting any sound like back firing? Replace plugs, check spark, post back.
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