500 MJ Posted January 4, 2009 Share Posted January 4, 2009 I'm trying to get my '90 MJ road worthy. It has been sitting in the woods since Thanksgiving, and it ran just fine then. I understand that gas goes bad, but I don't think that this is completely the case for me. In the past the truck has always started up just fine, in fact it turned right over when I went to retrieve it from the woods this last week. In driving it around the driveway while I have been working on it, it has recently began to start very hard. I ran it down the road today and it stalled three times on me in the 2 mile drive I took it on and it took forever to start after each time it stalled. Once it started it ran just fine. After putting it back in the garage for the night and trying to start it the next day, it now takes about a minute worth of cranking before it starts. Once it starts it only runs on a few cylinders for about 5 seconds and then the rest of them kick in. The truck only has 100,000 miles on it. The distributor cap is dry, but it does have a few spots of corrosion on it. I cleaned it and the rotor up with a wire brush. I don't think the problem is fuel related because there is plenty of fuel pressure in the fuel rail and the pump works good and primes right up before each start. I am starting to wonder if something has become gummed up or if something major is wrong with the computer :ack: ... running out of ideas, any help? Truck is a '90 with the 4.0L and 2wd AW4 trans. Everything is bone stock as far as the driveline goes... Link to comment Share on other sites More sharing options...
BLHTAZ Posted January 4, 2009 Share Posted January 4, 2009 If you are sure of a completely proper functioning fuel system including injectors & ballast resistor, them the only other thing left is fire... CPS could be going bad... Coil could be having issues... The CPS is my primary suspect because of the stalling issue and because of the "runs on a few cylinders for about 5 seconds" thing. Link to comment Share on other sites More sharing options...
CWLONGSHOT Posted January 4, 2009 Share Posted January 4, 2009 I am going to guess you have some "house" guests. More specfically MICE!! They LOVE vehicles parked in the woods and likely shewed thru or partially thru some wires... Have fun finding where they did that!! Sorry man, I have seen it many times before... CW Link to comment Share on other sites More sharing options...
james750 Posted January 5, 2009 Share Posted January 5, 2009 I am going to guess you have some "house" guests. More specfically MICE!! They LOVE vehicles parked in the woods and likely shewed thru or partially thru some wires... Have fun finding where they did that!! Sorry man, I have seen it many times before... CW I've seen worse than mice, When I was fixing up my sisters XJ I pulled the rear left trim piece and found a ton of chewed up foam. when I took off the right piece a live gopher jumped out and ran off. I was shocked. :clapping: Link to comment Share on other sites More sharing options...
phenryiv1 Posted January 5, 2009 Share Posted January 5, 2009 Mine also starts hard, and we replaced nearly everything- starter, distributor, rotor, alternator, battery. I don't know what finally got it to start reliably (my father had it "woprking" about a year before I bought it), but it used to not re-start if it had run for more than a few minutes at any speed. Now, that has been rectified. I will look through the receipts to see if I can get a clue as to what finally fixed it. Link to comment Share on other sites More sharing options...
500 MJ Posted January 6, 2009 Author Share Posted January 6, 2009 I took it down to a mechanic today and now $50 later I still don't have an answer. Prior to having the problem I noticed that the connection in the wires to the fuel pump had been spliced together with "butt" connectors. I cut these out, one at a time and soldered in a connector in their place. Only after I did this and messed around under the truck doing other things did the problem start to occur with the hard starting. Could the solder gun have hurt the fuel pump enough that it weakened it so it isnt giving me all the fuel I need? The fuel pressure seemed good when we hooked up the gauge to it and let the truck prime up before starting, but I'm wondering if the pressure isnt holding when we go to start it... Any thoughts? I probably should have said something about the soldering but I didnt think it could hurt anything... much less cause a problem, in fact I soldered everything up so that it wouldnt cause a problem :( Link to comment Share on other sites More sharing options...
500 MJ Posted January 15, 2009 Author Share Posted January 15, 2009 Well, I am back up at college now. I licensed the truck and drove it around town for a few days, still starting hard, and then tried to drive it back to college. It didnt make it. I stopped at a rest stop along the freeway. It was running just fine so I shut it off and went in to do my thing. Came back out and it WOULD NOT START. I was about an hour down the road at this point. I spent about an hour trying everything I could think of to get it to start but it just wasn't in the stars I guess. So I had my parents come and pick me up, we towed the truck home. Once we got it home I figured I would just see if it might possibly start. It did. It ran rough then cleared up and ran fine, just like before. :wall: Not wanting to trust it, I pulled it back out into the woods and thats where it will sit until I get the chance to mess with it again! I'm not too happy with that truck at the moment. On the plus side, I put the battery back in the '88 and it fired right up. Drove it to the Sec. of State to swap plates the next day and then continued on with the full 420 mile trip back to college. :bowdown: Guess it is destiny to have the 4wd machine up here to play around in the snow with and leave the 2wd one back at home... Link to comment Share on other sites More sharing options...
Ed in North Ga. Posted January 15, 2009 Share Posted January 15, 2009 Generally, renix`s are finiky if you don't use them. They like to be run, preferably every day, to last a long time. If you let one sit for a month, all kind of gremlins poke their heads up. First thing- the gas comes out- its not good enough to burn anymore- in a renix. Drain the tank, fill with a gallon of the fresh stuff with some stabil in it - second- full throttle body clean out- pull the IAC and clean the pintle, pull the TPS and check the Ohms- clean the bore of the IAC pintle seat, and then clean the bore of the Throttlebody- there will be a carbon ring where the butterfly sits, and its now gummed up from sitting- AND clean the back side of the butterfly plate- I use Tolulene and a toothbrush. Third, remove all the air from the fuel rail at the schreader valve, and check the backside vacuum port on the fuel pressure regulator- if theres gas on the vacuum side, replace. You may end up with tank gunk- leave one sit too long and water mysteriously appears in a tank...worse than that are "friends" who think you need some sugar or dirt in the tank...such nice people- luck to ya- Link to comment Share on other sites More sharing options...
500 MJ Posted January 16, 2009 Author Share Posted January 16, 2009 Anything is worth a shot, thanks for the info! Will be awhile before I get to try it out though... Link to comment Share on other sites More sharing options...
500 MJ Posted March 12, 2009 Author Share Posted March 12, 2009 Sooo...I'm calling in an exorcist. I am pretty sure my truck is possessed. :evil: Fuel pump has good pressure and my gas is GOOD. I Put in a new mopar CPS this evening. Still having the problem with hard starting. Any more ideas?? Tomorrow I am going to go get plugs, wires, cap and rotor and try that route, also will clean the TB out like Ed described above - haven't gotten to that yet :ack: Link to comment Share on other sites More sharing options...
Windowsrookie Posted March 12, 2009 Share Posted March 12, 2009 Sooo...I'm calling in an exorcist. I am pretty sure my truck is possessed. :evil: Fuel pump has good pressure. Put in a new mopar CPS. Still having the problem with hard starting. Any more ideas?? Tomorrow I am going to go get plugs, wires, cap and rotor and try that route :ack: Test for spark, if it has good pressure it has to be spark. Are you sure the CPS is seated properly, are you sure it's a Renix CPS? Link to comment Share on other sites More sharing options...
500 MJ Posted March 12, 2009 Author Share Posted March 12, 2009 Sooo...I'm calling in an exorcist. I am pretty sure my truck is possessed. :evil: Fuel pump has good pressure. Put in a new mopar CPS. Still having the problem with hard starting. Any more ideas?? Tomorrow I am going to go get plugs, wires, cap and rotor and try that route :ack: Test for spark, if it has good pressure it has to be spark. Are you sure the CPS is seated properly, are you sure it's a Renix CPS? Yes, I installed it back in the top of the bellhousing with the correct bolts. Is there a gap that it needs to be adjusted at? I've never heard of any adjustment for them??? I am also sure it is a Renix CPS , it looked EXACTLY the same as the one I took out of the truck... Link to comment Share on other sites More sharing options...
Pete M Posted March 12, 2009 Share Posted March 12, 2009 Did you plug it into the factory harness? Or do the update modification to wire it directly to the ECM? Link to comment Share on other sites More sharing options...
500 MJ Posted March 12, 2009 Author Share Posted March 12, 2009 Its in the factory harness, what update mod? Was this a recall or something? Link to comment Share on other sites More sharing options...
Eagle Posted March 12, 2009 Share Posted March 12, 2009 It wasn't a recall, but there was a TSB (Technical Service Bulletin). Apparently there's significant enough current losss in the factory harness that Jeep came out with a separate, stand-alone harness that runs directly from the CPS connector through the firewall into the ECU. The harness should still be available from Jeep dealers. Link to comment Share on other sites More sharing options...
500 MJ Posted March 13, 2009 Author Share Posted March 13, 2009 Messed with it some more today. I cleaned all the ignition parts up as well as the throttle body today and it didnt help anything. I figured I would go into town and start buying more new parts/sensors but before I took off I figured I would see how much gas I had in the fuel rail. So I hit the valve and it drained a bit off and then proceeded to try and start it. AND IT DID - Like it never had anything wrong with it at all. Ran just fine and smooth as glass. I was awestruck. Shut it off and tried it again - took right off. So I set there thinking what the in the world could be going on here. I let it idle while I did this and after about 5 minutes it started running rougher and eventually it died. This puzzled me more. So I tried to start it and it wouldnt go. Went back under the hood and drained the gas from the fuel rail again. Tried to start it and it took off and ran fine. So this has me thinking about what the culprit could be. Tomorrow I'll be swapping out my fuel rail and changing it with another one I have. I'm doing this to see if it could be the regulator. Also after I inspected things fruther, I noticed one of the fuel injectors has been replaced while the other 5 are the stock ones. It looks like it was a replacement for a stock part but I don't know how I tell if its the correct replacement or not. Would this be something to worry about or not? I'm getting closer - its taking some work though :banana: Link to comment Share on other sites More sharing options...
MiNi Beast Posted March 13, 2009 Share Posted March 13, 2009 Check the fuel pressure before swapping the rail. :dunno: Link to comment Share on other sites More sharing options...
500 MJ Posted March 23, 2009 Author Share Posted March 23, 2009 Well, I swapped the fuel rails and it didn't resolve anything. So I left it at that and replaced my front wheel bearings so I could at least say I got something accomplished on it while I was home on Spring Break. Now at least I can drive it without listening to the humm of the bad ones I had. I left it at home for my Dad to see what he could come up with to get it to work. He is as puzzled as I am about what the problem is now. I am thinking that there is a blockage in the return fuel line somewhere that is not allowing the fuel to return to the tank - how likely is this? Dad seems to think that my problem still lies in a sensor somewhere. So far I've replaced the CPS and the CTS on the truck. While I was replacing the CTS I noticed that the knock sensor was fubared up - I don't exactly have lots of cash to throw at it right now, figured I would replace it later. Could that have anything to do with this? What other sensors control the amounts of fuel sent to the engine? Dad got ahold of me today (we are 8 hours away right now - me at college again and he is at home) and let me know his findings so far. He has put a pressure gauge on the fuel rail and he gets these readings: running 32 psi, after it's shut off 40 psi. He has to shut the truck off and then look at the gauge so it takes him a second or two to shut it off and then check the gauge under the hood. Are these numbers in the ball park range? I can't imagine that the fuel pump is weak because ALL of the spark plugs are BLACK when you pull them to check them and I've got all kinds of black wetness/stuff shooting out of the tailpipe. Both of those signs tell me that there is TOO MUCH fuel getting sent to the engine, but aren't RENIX fuel pumps supposed to supply around 45 psi? Anyone out there have any more thoughts? Link to comment Share on other sites More sharing options...
Geonovast Posted March 23, 2009 Share Posted March 23, 2009 Have you done anything with the MAP sensor? If that's gone bad it could be dumping way too much fuel. Link to comment Share on other sites More sharing options...
500 MJ Posted March 23, 2009 Author Share Posted March 23, 2009 I did swap the one in from my '88 and it didnt resolve anything. I did that last year when I first started having the problem... Link to comment Share on other sites More sharing options...
Geonovast Posted March 23, 2009 Share Posted March 23, 2009 O2? Link to comment Share on other sites More sharing options...
terrawombat Posted March 24, 2009 Share Posted March 24, 2009 Your truck seems to be exhibiting very similar symptoms that my '88 4.0L did about a month ago. I was banging my head against a wall because the thing ran fine months prior, but then wouldn't start up at all and would constantly foul up the plugs. I think issue turned out to be bad gas. I removed the fuel tank from the truck, removed the fuel pump, and drained ALL of the gas. Put fresh stuff in, cleaned up all of the plugs, and the truck fired right up, although it still seems to be running on the rich side. It looks like you've already went down this route so it probably won't help you too much, but I'm curious to see if you can isolate the problem. I also had a colder thermostat in my truck (180 degree) and swapped that out for a stock one (195 degree). These trucks use coolant temperature as one of the main ways of determining the fuel/air ratio and if the truck constantly runs cold, the computer will run it rich. Your fuel pressure readings seem to be in the ballpark. I'm pretty sure with the truck running and the vacuum line disconnected from the regulator, you should see about 39 psi. With the vacuum line on, it should drop down some (I think mine runs in the 25-28psi range, but I can't quite remember). When you shut the truck down, does the fuel pressure drop to 0psi or will it hold at 38-40psi? If it drops to 0psi right away, then you know you've got an issue with the fuel system somewhere. When you kill the engine, the regulator is supposed to shut off and hold pressure so that when you go to turn the truck on in the future, the rail is already pressurized and ready to go. Link to comment Share on other sites More sharing options...
Geonovast Posted March 24, 2009 Share Posted March 24, 2009 It will only hold pressure for a few seconds. The pressure will bleed off through the return line. Regulator only manages one line. Link to comment Share on other sites More sharing options...
500 MJ Posted March 24, 2009 Author Share Posted March 24, 2009 It sure does hold pressure :rant: :wall: :mad: :fs1: I havent checked for how long but it holds it for a LONG time. The thing that gets me is that it only started doing this when I went under it and soldered up the P.O.'s connection of the three wires to the fuel pump (they were connected with Butt connectors and were starting to corrode, I don't know where the all weather connector went :dunno: ) Anyway, before I did this it never had problems starting. I would leave it sit in the woods for MONTHs on end and it still fired right up after a few seconds. Since I've had the problem I've been forced to replace a few things and it runs much better than it ever has, once it starts up. Somewhere along the line the cough and sputter problem for a few seconds after starting that I got after I soldered the wires has disappeared (My guess is that it was the cleaning of the dist/throttle body). So now when we can get it to start it will roll right over and take off just like my '88. But the problem now is that too much fuel is in the rail for it to run properly and I just am running to my wits end trying to figure it out... I'll see what Dad thinks about the Oxy sensor... Thing is that quality Sensors aren't cheap and I've replaced a few of them now that has done nothing for the problem. :wall: Thanks for your thoughts guys! Please Keep 'em coming! Link to comment Share on other sites More sharing options...
terrawombat Posted March 24, 2009 Share Posted March 24, 2009 It will only hold pressure for a few seconds. The pressure will bleed off through the return line. Regulator only manages one line. Mine will hold pressure for quite a while before it gradually bleeds off to zero. The regulator is attached and manages the return line. There should also be a check valve in the fuel pump which won't allow the fuel to bleed back through that line. With the engine shut down, the injectors should also all be shut, thus your pressure should be maintained. Notice the large use of the word 'should.' Link to comment Share on other sites More sharing options...
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