JeepcoMJ Posted June 2, 2008 Share Posted June 2, 2008 first off, i haven't really troubleshot this too much. picked up a 87 shortbed that's been in a barn for the past 7 or 8 years. it's a 4.0 auto 2wd. was told it doesn't run (bull i got it running in 2 hours of futzing around with fuel delivery) it idles great. but beyond that, nothing. if you give it more than 1/8 throttle, it sputters, misses, dies out. i've swapped MAP sensor, throttle body, and fuel filter and those don't seem to be the problem. the fuel pressure at the rail at idle is 32PSI and it gets a bit sporadic when using the throttle. so i'm leaning towards it being a bad fuel pump which is sending pressure but not volume, or possibly a CPS. the spark plugs are new with .035 gap, new wires cap and rotor. I'm really not sure what it could be...i even chopped the exhaust off hoping that might fix it. ideas? Link to comment Share on other sites More sharing options...
Geonovast Posted June 2, 2008 Share Posted June 2, 2008 7 year old gas. Link to comment Share on other sites More sharing options...
Eagle Posted June 2, 2008 Share Posted June 2, 2008 7 year old gas. DING! Link to comment Share on other sites More sharing options...
BLHTAZ Posted June 2, 2008 Share Posted June 2, 2008 7 year old gas. DING! My thought too as putting fresh gas in was not mentioned. If it has fresh gas, then I would agree with fuel pump as the likely culprit. Link to comment Share on other sites More sharing options...
JeepcoMJ Posted June 2, 2008 Author Share Posted June 2, 2008 tank was empty it's running premium...around 5 gallons of it... Link to comment Share on other sites More sharing options...
metrictonner Posted June 2, 2008 Share Posted June 2, 2008 Empty tank for all those years? Maybe the fuel pump is trying to suck in a lot of rust. :jump: Link to comment Share on other sites More sharing options...
possum Posted June 2, 2008 Share Posted June 2, 2008 Not very likely but the premium fuel could be messing with it also. Older computers are kinda funny that way. :dunno: Link to comment Share on other sites More sharing options...
mvusse Posted June 2, 2008 Share Posted June 2, 2008 Yeah, I'm guessing you got plugged (pick any 3 of) fuel filter, fuel lines, injectors. Sitting for 7 years whatever gas was in it probably slowly evaporated, leaving powdery residue behind. That stuff may not redisolve completely, and might be fine enough for some if it to go right through the filter, Link to comment Share on other sites More sharing options...
JeepcoMJ Posted June 3, 2008 Author Share Posted June 3, 2008 Yeah, I'm guessing you got plugged (pick any 3 of) fuel filter, fuel lines, injectors. Sitting for 7 years whatever gas was in it probably slowly evaporated, leaving powdery residue behind. That stuff may not redisolve completely, and might be fine enough for some if it to go right through the filter, :eek: :cry: guess it's time to pull the system apart... Link to comment Share on other sites More sharing options...
Car RamRod Posted June 3, 2008 Share Posted June 3, 2008 Not very likely but the premium fuel could be messing with it also. Older computers are kinda funny that way. :dunno: Agreed. It's made to run on 87, 89 at best. Anything over that is hurting more than helping, though that may not be the problem here. Link to comment Share on other sites More sharing options...
chicofuentes0224 Posted June 3, 2008 Share Posted June 3, 2008 Not very likely but the premium fuel could be messing with it also. Older computers are kinda funny that way. :dunno: Agreed. It's made to run on 87, 89 at best. Anything over that is hurting more than helping, though that may not be the problem here. What would running 91 octane or higher hurt? Link to comment Share on other sites More sharing options...
Geonovast Posted June 3, 2008 Share Posted June 3, 2008 It's burning "too well" and the computer wouldn't know what to do with it. Link to comment Share on other sites More sharing options...
chicofuentes0224 Posted June 3, 2008 Share Posted June 3, 2008 It's burning "too well" and the computer wouldn't know what to do with it. I'm sorry. I'm not trying to be smart here, but I still don't get it. I've run 87, 89, 91, 93, 94 octane and the higher the number the smoother my engine seems to run. I'm not a mechanic and know nothing of octane ratings. Somebody school me. Link to comment Share on other sites More sharing options...
comancheman Posted June 3, 2008 Share Posted June 3, 2008 i also notice a difference when i run premium gas it deffenitley runs smoother. also jeepco my first mj did the same thing to me after it sat for a few years and it turned out to be the cps. Link to comment Share on other sites More sharing options...
Car RamRod Posted June 4, 2008 Share Posted June 4, 2008 It's burning "too well" and the computer wouldn't know what to do with it. I'm sorry. I'm not trying to be smart here, but I still don't get it. I've run 87, 89, 91, 93, 94 octane and the higher the number the smoother my engine seems to run. I'm not a mechanic and know nothing of octane ratings. Somebody school me. Well generally, higher octane means it has a higher flash point, so to speak (I don't recall the exact phrases here). In other words, ideally, an engine with compression, spark, timing built to run on 87 will be more efficient on the 87 that ultra 94. http://www.listangs.com/forum/viewtopic ... 30&t=23352 But also have to keep in mind, these are jeeps, and they have minds of their own. Link to comment Share on other sites More sharing options...
Randy in Maine Posted June 5, 2008 Share Posted June 5, 2008 May also have rust in the fuel tank and munged up fuel injectors. I woiuyld send them to www.cruzinperformance.com and get them cleaned and calibrated. It should run better on 87 octane fuel. Link to comment Share on other sites More sharing options...
JeepcoMJ Posted June 5, 2008 Author Share Posted June 5, 2008 May also have rust in the fuel tank and munged up fuel injectors. I woiuyld send them to www.cruzinperformance.com and get them cleaned and calibrated. It should run better on 87 octane fuel. haha. i'm cheap, i don't pay for things like that to be done. i'd rather play musical injectors with my parts engine ;) thanks though. draining the tank and pumping the lines dry along with swapping in a different fuel rail and injectors. none of this costs $$$ just time... Link to comment Share on other sites More sharing options...
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