88 Beast Posted February 13, 2013 Share Posted February 13, 2013 I think my fuel pump is going out. 88 MJ, 4.0 L, Left me on the side of the road yesterday. Started back up, ran for a minute then sputtered and died. Did some prilimary checks. Getting power through resistor, can hear pump running when engine sputtering. Haven't checked pump ground or pressure yet, but did have alittle pressure in fuel rail after it dies when I press schrader valve. Will do more t/s this weekend. Question is does anyone have p/n of correct pump as I've read here of pumps being for Cherokee's and not MJ. This is my DD so I want to get the right one the first time. I usually get my parts through NAPA and they list 3 or 4 different p/n's. Any help would be great. Thanks. Link to comment Share on other sites More sharing options...
Biotex Posted February 13, 2013 Share Posted February 13, 2013 My buddy just installed one from NAPA. It came with the sock and was almost a bolt on direct fit. Couple of issues. the o-ring to seal the tank back up was too thick, so he ended up using the original one. He had to use a dremel to reshape a part that keeps the pump from spinning in the part that holds it in place. Very minor things. His old pump was only making 18 psi, the new one fixed it. Link to comment Share on other sites More sharing options...
comanchedude Posted February 13, 2013 Share Posted February 13, 2013 To my knowledge there is 1 style..they may have 3 options ..like Bosch ,carter ect. On the pumps they have the cheaper type and the factory Bosch type witch is a turbin pump..the cheap units use gear or roller type pump..they all will work but for the fuel pump I always recommend the Bosch pumps.thats what I replaced mine with and they are top line..and they cost more expect to pay 70 to 90 for Bosch unit..cheap units are like 20 to 40 ..but I think you should spend the extra bucks if you can on the better pump. Prices are online rock auto ..that's we're I buy most stuff. I think my fuel pump is going out. 88 MJ, 4.0 L, Left me on the side of the road yesterday. Started back up, ran for a minute then sputtered and died. Did some prilimary checks. Getting power through resistor, can hear pump running when engine sputtering. Haven't checked pump ground or pressure yet, but did have alittle pressure in fuel rail after it dies when I press schrader valve. Will do more t/s this weekend. Question is does anyone have p/n of correct pump as I've read here of pumps being for Cherokee's and not MJ. This is my DD so I want to get the right one the first time. I usually get my parts through NAPA and they list 3 or 4 different p/n's. Any help would be great. Thanks. Link to comment Share on other sites More sharing options...
Akula69 Posted February 14, 2013 Share Posted February 14, 2013 #2 to recommend the Bosch pump - the only real difference I had with the '899 installation was I had to shorten a rubber fuel hose (from pump to sender). Otherwise - it was a breeze. Took longer to get the dayn thing out them replace the pump! Link to comment Share on other sites More sharing options...
88 Beast Posted February 23, 2013 Author Share Posted February 23, 2013 Working on it again now as we speak. Replaced pump last weekend. Ran it in garage for about 30 minutes, seemed to have good fuel psi. Took it for a drive and it died about a mile down the road. Made it home after a dozen stall outs. Fuel just dribbling from test valve. Pissed off and let it sit until today. Bought fuel press.gauge. Pressure reads good, 32 psi with vacuum hooked to reg. and 40 psi without. Have been running engine for 45 mins. at different RPM and press. holding good. Checked pressure leakdown at regulator, psi does drop below maximum allowable psi. in 30 min. with engine off. My question is, would this cause fuel press to drop off to next to nothing while driving? I'm about to take out for test drive again. Link to comment Share on other sites More sharing options...
Biotex Posted February 23, 2013 Share Posted February 23, 2013 What kind of shape is the filter in? Possibly clogged? Also, don't rule out intermittent electrical issue. Link to comment Share on other sites More sharing options...
87manche1 Posted February 23, 2013 Share Posted February 23, 2013 Bleed down is normal usually around 12 psi. Test fuel pressure with it running driving stick gauge on windshield then go from there. But I would start looking at other areas. Clogged cat? Electrical issue? Sensor? Link to comment Share on other sites More sharing options...
MtnClimber Posted February 23, 2013 Share Posted February 23, 2013 Sounds like a clogged fuel filter. My .o2c Link to comment Share on other sites More sharing options...
88 Beast Posted February 23, 2013 Author Share Posted February 23, 2013 Just got back from 35 min.test drive. Ran great. Pulled into garage, let it idle. Removed tank cap to listen to pump, put back on. Couple of seconds later, started running like crap and died. Coincidence? Put fuel press. gauge on and started back up. Fuel pressure good but running bad. Checked for loose electrical connections. All seem okay. What now? Link to comment Share on other sites More sharing options...
88mjgilley Posted February 23, 2013 Share Posted February 23, 2013 sounds like what mine does but mine normally doesnt die Link to comment Share on other sites More sharing options...
Biotex Posted February 24, 2013 Share Posted February 24, 2013 Cap vent plugged? Link to comment Share on other sites More sharing options...
88 Beast Posted February 24, 2013 Author Share Posted February 24, 2013 Replaced cap about a month ago and fuel filter replaced prior to todays test drive. Been running in garage now for awhile and everything seems okay again. This is the first real problem with with this truck since I've had it 9 years now. I checked the MAP sensor per t/s guide I got online for Renix FI some time ago. The output voltage with key on/engine off is about 1 volt below spec. @ 3.6 v., should be 4.5-5v. Guide says to replace Map sensor but with engine running, output voltage @ idle is within spec. @ 1.1 v. Spec is .5 - 1.5v. Could being that 1v below spec cause my problem? Gotta get this thing figured out. Link to comment Share on other sites More sharing options...
Biotex Posted February 24, 2013 Share Posted February 24, 2013 Maybe you can swap the power latch relay with the fuel pump relay and see if that helps. Your fuel pump relay might be on its way out. If it were mine, I would figure out a way to hook up a voltmeter to the fuel pump so you can read the voltage while inside the cab. I'd verify full volts to pump when the problem happens. The idea being to eliminate components one at a time vs. throwing parts at it. I like to work in a linear fashion. Makes sense to start at the tank. These are the hardest to figure out, and I feel your pain. Once you know for a fact the pump is delivering full pressure at all times, then you will need to use your FI t.s. manual and go through it component by component. Sounds like you have been doing that. I honestly can't tell you if 1 volt below MAP specs will cause your problem. but look at it as a percent instead. Your about 20% off. Personally I don't think that is your problem, but could be wrong. Link to comment Share on other sites More sharing options...
88mjgilley Posted February 25, 2013 Share Posted February 25, 2013 my tank was rusty thats where all my issues came from Link to comment Share on other sites More sharing options...
88 Beast Posted March 2, 2013 Author Share Posted March 2, 2013 After letting it sit a week, back on it today. Started fine and had good steady fuel pressure and moved into garage. Cleaned C101 connector, was full of nasty. Ran in garage for half hour with fuel pressure gauge and VOM backprobed into fuel pump connector,all good. Then took on 60 mile, 1 hour drive. Got back to the house and let it idle for a bit. Fuel press. and voltage good. Then stumbled once but didn't die and smoothed out. I guess I'll drive it this week see what happens. Wish me luck. Also I want to run fuel pump back through resister as it is noisier without, I'm getting about 9 v. to pump with resister. Is this about right? Link to comment Share on other sites More sharing options...
88 Beast Posted March 26, 2013 Author Share Posted March 26, 2013 Well folks, thought I had fixed. Ran great for four days then back to it's old tricks. Weekend before last gave it a full tune up. Ran good for a day and then left me on the side of the road. Bucking real bad, backfiring I think through throttle body, then died. This time, smoke from under hood. Popped hood, engine not overheated or boiling over but could feel excessive heat and smell of hot metal. Felt tailpipe tip and was very hot. Plugged cat I thought? Would crank but not start. Had to sit on side of road for 45 min. before it would start. This is what usually happens. Let it sit then runs good. Got it home and this past weekend removed cat. Drove to work today and started doing it's thing about a mile from work but didn't die.Damn it! Drove home, ran good until almost home. Could O2 sensor or CPS cause this intermitent problem? Both were replaced about 3 years ago. This is really starting to get on my nerves as I've got ujoints and a unit bearing that needs replaced but I've got to figure this out first. Any ideas? Link to comment Share on other sites More sharing options...
JeepComancher Posted March 26, 2013 Share Posted March 26, 2013 (edited) Checked all grounds? (bucking real bad on 90 MJ 2wd, dirty neg cable at engine {Culprit found 4-15-13, loose wire at Fuel Pump!}) (I will be upgrading all grounds on all 3 of my 90 Jeeps...no other year ever gave me so many starting problems) Fuel Pump Resistor? Alternator tested? Read thru these: http://comancheclub.com/topic/36382-cruisers-renix-tips/ I think it may be electircal somewhere. P.S. (4-21-13) On which fuel pump, all aftermarket will have to be modified to fit. And you have to get a different filter(if it doesn't come with it). I sent all the Carquest, Napa, Crown(right length), Autozone, etc back to the stores. Of course, Chrysler sold the last one 2 weeks ago... I just bought the last ones Bosch had, they aren't sure if they will ever make more. JeepNut Edited April 21, 2013 by JeepComancher Link to comment Share on other sites More sharing options...
ftpiercecracker1 Posted March 26, 2013 Share Posted March 26, 2013 Checked all grounds? (bucking real bad on 90 MJ 2wd, dirty neg cable at engine) \ JeepNut THIS!! My 90 nearly got me killed on several occasions because of a bad ground. For me it was very intermittent, but when it had its little fits it would buck, kick, snort, backfire (literally blew apart my muffler) and just about every other god awful thing. Turned out to be the ground at the bottom of the dipstick, nut was three turns from falling completely off and was covered in oil and grime. After thoroughly cleaning said stud and connectors and retighting ALL symptoms went away and never have returned. This was after spending nearly a grand on other sensors and shop labor. :wall: Long story short CHECK YOUR GROUNDS! Link to comment Share on other sites More sharing options...
jimoshel Posted March 26, 2013 Share Posted March 26, 2013 Checked all grounds? (bucking real bad on 90 MJ 2wd, dirty neg cable at engine) \ JeepNut THIS!! My 90 nearly got me killed on several occasions because of a bad ground. For me it was very intermittent, but when it had its little fits it would buck, kick, snort, backfire (literally blew apart my muffler) and just about every other god awful thing. Turned out to be the ground at the bottom of the dipstick, nut was three turns from falling completely off and was covered in oil and grime. After thoroughly cleaning said stud and connectors and retighting ALL symptoms went away and never have returned. This was after spending nearly a grand on other sensors and shop labor. :wall: Long story short CHECK YOUR GROUNDS! I wouldn't bother checking any grounds. Just disassemble, clean, reassemble.All of them. Link to comment Share on other sites More sharing options...
ftpiercecracker1 Posted March 26, 2013 Share Posted March 26, 2013 I wouldn't bother checking any grounds. Just disassemble, clean, reassemble.All of them. Its what i ment jim, its what i ment. ;) Link to comment Share on other sites More sharing options...
cruiser54 Posted March 27, 2013 Share Posted March 27, 2013 Replaced cap about a month ago and fuel filter replaced prior to todays test drive. Been running in garage now for awhile and everything seems okay again. This is the first real problem with with this truck since I've had it 9 years now. I checked the MAP sensor per t/s guide I got online for Renix FI some time ago. The output voltage with key on/engine off is about 1 volt below spec. @ 3.6 v., should be 4.5-5v. Guide says to replace Map sensor but with engine running, output voltage @ idle is within spec. @ 1.1 v. Spec is .5 - 1.5v. Could being that 1v below spec cause my problem? Gotta get this thing figured out. Have you ever tested the sensor ground circuit, cleaned the C101 or refreshed your grounds? Link to comment Share on other sites More sharing options...
zackcj7 Posted April 9, 2013 Share Posted April 9, 2013 Have you figured this out yet? Link to comment Share on other sites More sharing options...
88 Beast Posted April 11, 2013 Author Share Posted April 11, 2013 Nope. I did all of Cruiser's wiring updates to the grounds, C101 cleaned, coil contacts cleaned,CPS cks. out,TPS adjusted correctly. Did have serious flucuations at the two ground circuits in the harness. Runs great for 35-45 mins. then engine temp starts to rise above normal. It starts to miss, backfire and eventually die. During my t/s with Renix Diagnostic info, sync sensor signal voltage test, key on w/engine off,I get varing readings. Should be 5v. I'll get 2v one time, 4.9v another and sometimes 7v, which is the input voltage from ECM. I've checked the harness from the sync connetor to the ecm and cks. out good. Could this be my problem. Has anyone taken this reading before? If so, could you let me know what you have. Getting a bit discouraged. Maybe ICM, dist.? Coil replaced last year but you never know. Don't want to start throwing parts at it. Need help. Link to comment Share on other sites More sharing options...
cruiser54 Posted April 11, 2013 Share Posted April 11, 2013 Unplug the dizzy and see what happens. How did you address the ground fluctuations when wiggling the harness? Link to comment Share on other sites More sharing options...
88 Beast Posted April 11, 2013 Author Share Posted April 11, 2013 Unplug dizzy while engine running? With it unplugged and engine off, I am getting correct ecm input voltage to dizzy, 7v. I repaired and soldered existing sensor ground crimps. This did fix the flucuation in the harness. Did not eliminate single wire and solder all together. By doing what you suggest, this eliminates going through C101, correct? I can do that no problem. Link to comment Share on other sites More sharing options...
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