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Discussion Starter #1
this is a 91 302 w/ E40D 4x4 4:10 axles w/ limited slip... its an f-150 with a 36xxx on the 5 digit odometer, but i dont think there are any differences that would change the diagnosis compared to a bronco

we just bought it, so the history is vauge, plus the guy lied about at least 2 things now:doh0715:... so theres no telling what is true.

the idle is at anywhere from 1400- 2000 rpm in park all the time, or around 1100-1400 in gear. this is what we have done so far:

replaced EGR
replaced IAC
cleaned throttle body
replaced MAP
replaced TPS: this is interesting.. when we took the old one off, compared to the pictures on "the ultimate TPS thread" the TPS was on backwards.. meaning flipped 180 degrees. before we replaced it, we did the voltage test and it started at 4 volts, and dropped to .75 volts WOT. so we installed the new one the correct way and re did the voltage test, now it checks out normal, .75 idle - 4 volts WOT. nothing changed about how it runs.. still in the same spot.

sprayed every vaccum line/ joint we could find with brake cleaner, trying to rev the engine and find a vaccum leak but was inconclusive. the idle changes a little (50rpm or less) on its own, if there were leaks they were too small to make a difference..

checked the EGR vaccum regulator, did the test where you unplug the wire harness, and check the vaccum at the egr valve. it did not change the vaccum (which was very weak) at the egr. it is giving code 33 but could either the egr sensor or the egr vaccum regulator cause a high idle?

we have performed the self test several times:


koeo:

33 - egr valve opening not detected

Cont. memory:

334 - DPFE or EVP circuit above the closed limit of 0.67 volts.

128 - MAP sensor vacuum was not greater than 2 in-Hg (7 kPa) during normal vehicle operation.

KOER:

code 4 (engine V8)

411 - Cannot control rpm during KOER low RPM check

412 - Cannot control rpm during KOER high RPM check

truck starts fine everytime, and drives ok, at idle w/ no brakes speed is 35 (and it shifts! :shockedscary)

any ideas on what should be tested next? i will keep searching.

thanks:beer
 

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It sounds to me like a definitly a vaccum leak somewear. I think I Would start checking the vacuum tree, maybe pull all vacuum lines off and put some tape on the tree to cover the holes to see how it idles and if it changes anything. Get a vaccum gauge also and hook it up to see what kind of vaccum your getting. My guess would be maybe a leak to your MAP sensor or your EGR since you got codes for those.
 

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Discussion Starter #3
good idea. i just did that, and the idle did not change. i took everything off the tree and taped the inlet tubes, and no change. what else could be leaking? intake gasket? i forgot to mention i replaced the throttle body gaskets, and i have the intake hoses off of the throttle body, and i put my hand over the throttle body tubes to stop the air, and it dropped the rpm to 1000 but didnt die. i guess that means it has a major air leak somewhere else?


and it has one of those stupid throttle body spacers on it (thats why theres 2 gaskets)

thanks for your input
 

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Def sounds like a vacuum leak, Maybe a slight crack in the manifold?
 

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Check your pcv valve next. Its a pain in the arse to get to and put back in. Maybe its not in place? Its under your upper intake.
 

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Discussion Starter #6
update: after convincing myself it was worth doing, i removed the plenum and there was about 40% of the upper gasket remaining. i guess that means the engine burned the parts that fell in? this must be the problem right?


i am going to replace the passenger valve cover gasket and the pcv before i put it back together, btw the hose for the pcv had massive cracks in it.. could that add to the vaccum / idle problem?

and last, the hose for the egr was BROKEN, not cracked.. could this add to a vaccum problem? its defenantly the code 33 problem, right?

now that i have the plemum off, is there anything i can do to it to improve it? it makes this more worth my time if i can upgrade at the same time

thanks for the input guys.
 

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For like $400.00 you could by the edlebrock intake manifold kit, but you've got to take off the lower intake for that.
 

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If my reading and memory serves me correctly, the code 33 for the valve not opening is detected from a sensor near the cannister or can or something... not by the egr sensor. I may be wrong, and I'm sure steve'll correct me if I am..
 

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Discussion Starter #9
the sensor was replaced, and so was the pressure regulator for the egr... and so was the actual egr valve

i know for example, on the chevy 5.0 plenum there are several things you can do to increase the amount of air that passes through it. anything like that on the ford 5.0? other than the ededbrock? (good advice dave, just short on cash)
 

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Discussion Starter #10
so i said screw it. the plenum gasket is for sure the problem, but i went klepto on my credit card the other night and bought the edelbrock plenum/ intake manifold, wiesco shorty headers, edelbrock 60379 aluminum cylinder heads, all new gaskets and pretty chrome edelbrock valve covers!.... i spent around $2500 and they gave me free shipping and a free hat! (ha)

taking apart the intake manifold 2 of the 4 outer intake bolts broke and left threads in the factory cylinder heads, and getting the #8 passenger side exhaust manifold bolt off was a 4 hour project (tight spaces) but im well on the way to having a mean 5.0.


i didnt need the cylinder heads, the intake manifold or the plenum replaced, i just wanted to boost the HP and torque. i drove the truck home it just had a high idle. if anyone is interested in the factory cylinder heads, factory intake manifold or factory plenum (all in perfect working order) send me a PM and an offer i would love to get some of this credit card bill paid off! i will ship parts if you pay the shipping.

sorry, the exhaust manifolds were trashed. BTW all came off of a 1991 f-150 5.0L 302ci v8 with 136xxx miles. the cylilnder heads have 1 broken bolt in threads from intake manifold on either side (meaning 1 on each side), can be removed. this is a common problem.


but i am excited to get this truck back together. looking for a 6'' lift after this CC bill is paid off. this truck has factory limited slip 4.10's so were excited to get it in the dirt! thanks to everyone this site has aided our progress 10 fold the haynes/ chiltons.
 
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