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Discussion Starter #1
hi. i just purchased a '88 bronco with a 5.0 in it. i got it cheap and it needs some work. ill include as much info as i can. like i said, it has a fuel injected 5.0, 4x4, auto tranny. the truck starts right up and runs pretty good. when you hit the gas and let go, it backfires out of the intake and it running really rich. it fouls plugs fast and blows clouds of smoke out of the exhaust.

i checked a few things to try to get an idea of a problem. first, i did a compression test. it was within an acceptable range i think. varied between 110 psi and 145 psi. i changed spark plugs, wires, distributor cap and ignition rotor cause it needed that stuff. i checked the ignition timing and fuel pressure and everything was good.

does anyone have any ideas on why the truck would be running so rich? it has some tapping coming from the engine, but if it had a valve problem, i would think a compression test would show that. if it was a lifter, cam or rocker problem, i would expect a misfure. it revs smooth from idle up to about 4k rpm, with no miss of hesitation.

i would appreciate any suggestions. maybe a computer problem? i have a parts truck im about to get ahold of. on top of that, i have a spare 5.0 engine, but i would like to do as little as possible in the way of swapping parts since this is just my beater truck for now.
 

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What if you have a problem with one (or more) of the injectors sticking open.....do all the plugs look fouled or just a few???

Did you pull the codes????
 

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Discussion Starter #4
every plug was fouled. i would think if it was a fuel pressure regulator problem, the fuel pressure would be high, which its not. if an injector(s) were sticking, it would have a had start, no? it fires right up. just runs extremely rich and backfires out the intake

i didnt try pulling codes yet. i will do that monday. it didnt have a check engine light on and i know the antiquated self diagnostics dont usually help. i will give it a try though. i would rather confirm no codes rather than ASSume there are none and have it come back to bite me
 

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Definitely check the codes, both KOEO and KOER.If the fuel pressure regulator is bad, It could cause low fuel pressure, which would make it lean, which could cause a backfire. If the o2 sensor reads a lean, the computer will try to enrich the mixture and make it too rich because the fuel pressure is incorrect. So, it could go either way. Also look for any vacuum leaks, especially going to the MAP sensor. Another thought, make sure there is no gas coming through the regulator diaphragm. That could make it really rich.
 

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Discussion Starter #6
hmmm. i expected a bad pressure regulator to cause high pressure. the pressure was a little on the low side with just the key on. maybe 25 psi. ill double check it while the truck is running. i cranked it and checked and i think it hit 40+ psi. i will definately run both tests on the computer. ill double check the MAP sensor again. i actually swapped it out cause i have a few extras and it made no difference
 

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Discussion Starter #7
what should be the fuel pressure reaction when i unplug the vacuum from the regulator? i want to try that also. from what i remember, the pressure should jump up. ill check the fuel pressure again while the truck is running. i checked it with the key on and with it cranking while i was doing a compression test. like i said, it seemed a little low when the key was on, but once i cranked it, the pressure jumped up to 40+ psi
 

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Is the '88 MAP (Speed Density) or MAF? If MAP, then I've had the same proble due to vacuum leaks. If the MAP sensor is seeing low vacuum then the engine thinks that the fuel demand is higher than it really is and runs on the 'load' part of the fuel map....way toward the rich side. A bad MPA will usually set a code but a MAP that has low vacuum will not. The otherr culprit could be thje O2 sensor...and even the coolant temp sensor..heck, even the IAT sensor. they all tell the ECM wheter to richen or lean out the injector pulse-width. But bad MAP vacuum has been the #1 culprit in the ones I have effed with. Again..assuming it is a SD setup...I'm not up on what years exactly were what..
 

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Discussion Starter #10
yes, it does have a MAP sensor. i will have to look closer at the vacuum hoses. i actually swapped out the MAP to see what happeded. i have a few ideas of stuff to check now. more are appreciated. i will look at the suggestions tomorrow at work
 

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Discussion Starter #13
i didnt set the timing it looked to be about 10*, which is what alldata called for. the timing was close enough to not be a problem. it didnt jump around or anything when i had the timing light on it. the truck doesnt deisel when you shut it off and starts right up when you start it. how would you check the fpr?
 

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Might want to check your vacuum lines too. If you have the C6 definately check the vacuum modulator line.
 

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mikec said:
i didnt set the timing it looked to be about 10*, which is what alldata called for. the timing was close enough to not be a problem. it didnt jump around or anything when i had the timing light on it. the truck doesnt deisel when you shut it off and starts right up when you start it. how would you check the fpr?

Check for gas in the vacuum line..Apply vacuum to it and see if it will hold X amount of vacuum..
 

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Discussion Starter #16
ok. popular opinion says to check the fpr and vacuum lines. ill jump on that tomorrow. ill let you guys know what i come up with. the frp should hold vacuum right? i have a vacuum pump. if it doesnt hold vacuum, the diaphram has a leak, correct?

the c6 tranny is a 4wd drive unit? does it come in 2wd or is that a c4 or aod unit?
im not too familiar with fords. i know basics from working on them, but more knowledgeable with GMs
 

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They all come in 2wd and 4wd versions. The trans is essentially the same, just a different tailshaft to allow it to bolt up to the transfer case.
 

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Discussion Starter #18
fpr holds vacuum. i put 20" on and it held good. fuel pressure was hovering just over 40 psi at idle. i was wrong about the popping. its coming out of the intake at accel, not decel. got a broekn vacuum line or 2, but they both look like pollution control stuff. ill plug then and run diagnostic tests and see what happens
 

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Discussion Starter #19
this thing is giving me a hard time. i got an ECT code from the computer. i know that will cause it to run rich, but im also concerned about the back firing out of the intake. i feel the 2 are related, especially for the amount of black smoke that is coming out of the tail pipe on this thing. the lifters are clattering a lot, but i dont know if thats cause the oil is getting gas in it. i dont see how it could be a stuck valve since all cylinders have acceptable compression and there really insnt a misfire anywhere. all of the plugs keep fouling. only vacuum that i found disconnected so far was for the egr, so i plugged the solenoid near the fuel rail
 

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Discussion Starter #20
i give up. it has to be some sort of valve problem. ijust dont understand since compression is good and theres no misfire
 
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