This is my first post on here, folks, good to be here. If possible, I need your help with something. I just got a 1985 f150 with a 5.0L EFI engine (EEC IV and all that) AOD trans, and 1 fuel tank. This truck is having some runability issues such as stalling at first start, erratic idle, surging at idle and low speed, poor throttle response, and general part throttle loss of power under load and no load. This truck is one of the first EFI models apparently, as it only had the canister filter and the two pump setup - in tank booster and on frame high pressure. Having said all that, here's some of the things I've done. The former owner changed the tank and both pumps, and I've changed the canister fuel filter, did an upper intake cleaning, checked all vacuum lines (20" vac at idle), replaced a dead TFI module, cleaned and checked the EGR valve, cleaned and checked the IAC assembly, changed the plugs, cap, rotor, and wires (tune up), re set base timing to 10 deg BTDC, checked ohm and volt spec on the IAT, Coolant temp sensor, checked volt and scale on the TPS, and checked function on the knock sensor. Have you noticed that I haven't mentioned the fuel pressure yet? Well, I haven't been able to find a service port on this fuel rail. I have looked over the entire rail (even under the plenum) and there is no shrader port that I can find anywhere. Am I imagining this or has anyone else even heard of a 5.0 with no service port? Anyways, after all that checking, it is better, but only marginally. Being as I seem to be unable to check the pressure, on a whim I tried removing the vacuum from the regulator, which, if it was bad I assume, shouldn't have made any difference. Well, taking that vacuum line off made a HUGE difference. Idle smoothed out, power came back, part throttle response came back load or not, idle quality and power overall massive improvements, cold and hot. The only code I retrieved from the KOEO and KOER that even makes any relation to runability was 41, (the other codes were 31, 34, 77, and 25) and I assumed that was a bad O2 sensor, as my book lists that as no switching and too lean. Could the fuel pressure regulator be bad and cause insufficient fuel pressure? Would it be bad to continue running it like this with the vacuum disconnected? Could a single wire O2 sensor be causing the fuel pressure regulator to be malfunctioning to this degree, or am I just forcing fuel past the injectors and overriding the fuel curve enabled by the computer? Any ideas would be helpful, I seem to be at a standstill. Thanks in advance.
You might also try blocking off the EGR and see if that makes any difference.
The error code 34 says the EGR valve was open when it should not have been and that could cause a lot of your problems.
The O2 sensor has NO control over the fuel pressure regulator.
You might have a weak spring inside the fuel pressure regulator but I dough it.
I did plug the EGR for the time being as a precaution, but it showed no improvement when i did it. I got a 5.8L fuel rail from a friend today to swap over that has a port on it, so hopefully tomorrow I'll know something.
Thomas, search the site for EFI troubles in the 80-86 forum. Archion and I fought with similar problems on his 86 F150. The end result, after changing all kinds of stuff was to replace the TPS with a Motorcraft unit. His EGR vacuum and vent were chattering like crazy and the idle and running were atrocious. When you swap the fuel rail, you might want to look at the injectors. BTW, don't be surprised if it doesn't fit, 351s are wider than 302s. Your O2 sensor is loads of fun, it's in the back of the right exhaust manifold.
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Bill Vose (Old School Hot Rodder) 1986 F350 crew cab DRW 460ci EFI, E4OD, PMGR starter, 160 amp 3G alternator, 12X3 rear brakes, Traction lock 3.55
1995 Lincoln Continental (project car) http://www.oldschoolhotrodder.com
"growing old is inevitable, growing up is optional"
Today I finished changing out the fuel rail. Wow that was not fun. The 351 fuel rail was indeed wider, and due to the cold morning and many years of use, the vinyl line on the ends was very stubborn and did not want to compress. In the end, I won out. The line couplings on the new rail are springlock, unlike the originals which were the plastic socket/clip kind, so I had to re make the line ends to make it work. After lots and lots of scrubbing, fixing blown out pipes, rusted apart hardware, and the like, I got it running again. Surprise! The fuel rail gauge fitting is smaller than standard, making my gauge useless. Nevertheless, it runs even better now than with the old rail at it's best with the fuel pressure regulator vac disconnected.
One thing I'm curious about though, on the incoming pressure line, there was a cylindrical object about 1 3/4" long and about 3/4' diameter (looked like an inline fuel filter) and as I had to take the line off, I blew through it to check for an obstruction, not really expecting to find one. Well, there was one. I thought maybe that object was a check valve, but I could blow either direction with the same effort. In the course of modifying the fuel lines, I cut that object out. What was it? anyone have an idea?
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