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86 F150 5.0 running poorly

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sdhorton

86 F150 5.0 running poorly

I have read all the information I can find and nothing has led me to a cure for this monster. Our youth shooting club was donated this truck to use or to sell and I cannot get it to run right.
1986 F150 5.0 auto 4x4. starts and runs, Idles fair, WOT fair everything else poor. At idle if you jab throttle it will die instantly.
We have run KOEO and KOER test, have located and cleared several items. Replace TPS tested and cleaned IAC, Tested timing and advance functions, tested spark on all cyl, compression is somewhat weak and erratic running from 75 to 123 but the engine hasn't been run hardly at all for several years. Exhaust system is open, have replaced both fuel pumps with new. pressure running at about 34lb.
I would like to find a trouble shooting flow chart or tree chart. I do not have a manual and right now cannot get a hard copy sent to me very well. What else should we be looking at? I am about to run it off the end of the dock!
Thanks
Shane

85lebaront2

Re: 86 F150 5.0 running poorly

Administrator

Ok, first item, TPS, aftermarket or Motorcraft? My so and I went through a nightmare on his 86 F150, part of the problem was the aftermarket TPS. The 1986 system expects to see 1.0 V at closed throttle, I believe +/- .05 volts, and at 1.10 volts the EGR system comes in, meaning his was chattering the solenoid valves and surging at idle.

On your frame, just behind the high pressure pump is a reservoir and on dual tank models a switching valve. In the bottom of that is filter for the inlet of the high pressure pump. Does the truck have a "check engine" light? Or it may say "emissions", if it does codes can be read through that. Unfortunately most parts stores can only read OBD-II systems and that is an OBD-I system. The fact that you have been able to read them is a plus. I will see if I can find a good diagnostic chart and scan it so Gary can put it on the site.

Bill AKA "LOBO" Profile

"Getting old is inevitable, growing up is optional" Darth Vader 1986 F350 460 converted to MAF/SEFI, E4OD 12X3 1/2 rear brakes, traction loc 3:55 gear, 160 amp 3G alternator Wife's 2011 Flex Limited Daily Driver 2009 Flex Limited with factory tow package Project car 1986 Chrysler LeBaron convertible 2.2L Turbo II, modified A413

Frank Wyatt

Re: 86 F150 5.0 running poorly

Bill has some good insight there on the TPS. Two other quick observations, 34 lbs sounds low to me on the fuel pressure, so check the filter in the reservoir like bill said, and also look at the fuel pressure regulator. Check the vacuum line as it could be cracked, though I couldn't tell you how it would be affected. Also the compression readings seem low and uneven, but a little oil in the low cylinders and rerunning the compression test could give higher numbers.

1981 F 150 Custom 300 ci with a fully rebuilt 1968 240 head Carter YFA T-18 3.25 9" rear 2WD
dual gas tanks
1990 Lincoln Town Car 5.0 AOD
Home town Mc Kenzie, TN

sdhorton

Re: 86 F150 5.0 running poorly

In reply to this post by 85lebaront2

I will check on the brand of the TPS, it is likely NOT a ford part. Is there enough slot on the mounts to get much adjustment?
I have read about that filter before, I will have to put it back up on the hoist and look for it. There is an inline filter, and of course the filters or inlet screen on the new pumps we installed.
We don't have a code reader, we have been reading the flash codes. The only code we are getting now I think is a 552 which is the airA and airB solenoids system I believe.

85lebaront2

Re: 86 F150 5.0 running poorly

Administrator

Ok, no adjustment on the TPS, no slots, base idle is set with the IAC disconnected if I remember correctly, but spec is based on voltage at the TPS.

Filter is in the base of the reservoir, it unscrews for access. I was trying to find the thread on FTE where my son posted the PN for it, but no luck.

Bill AKA "LOBO" Profile

myrl883

Re: 86 F150 5.0 running poorly

Motorcraft FG-848. Now obsolete, but a parts store should be able to cross reference it. Only 1985 and early '86s had a filter in there. If there is no filter, the cover will be marked "DO NOT REMOVE".

Ford Parts Monkey since 1985
1981 F100 Flareside - Black, 302-4V Roller/AOD
1986 F150 Flareside - Medium Fire Red 302/AOD
1989 F150 Standard Cab 4x4 - Dk Shadow Blue 302/AOD
1993 F350 4x4 Crew Cab - 7.3 IDI/ZF-5
I think it's a sickness...

sdhorton

Re: 86 F150 5.0 running poorly

I feel sort of silly, the truck we are working on is a 91 model not an 86 as I earlier said. sorry for the screw up. I am also fighting similar problems on an 06 Chev and got them crossed up.

sdhorton

RE: 86 F150 5.0 running poorly

In reply to this post by 85lebaront2

Bill, did you get the message that I gave you the wrong year model on that truck? I am working on another rig too and got them crossed up.

This F150 is a 91 model with the 5.0 engine.

Sorry if I wasted your time.

Shane

From: 85lebaront2 [via Bullnose Enthusiasts] <[hidden email]>
Sent: Monday, April 6, 2020 12:46 PM
To: sdhorton <[hidden email]>
Subject: Re: 86 F150 5.0 running poorly

Bill Profile

"Getting old is inevitable, growing up is optional" Darth Vader 1986 F-350 460 converted to MAF/SEFI, E4OD 12X3 1/2 rear brakes, traction loc 3:55 gear, 160 amp 3G alternator Wife's 2011 Flex Limited Daily Driver 1994 Taurus LX Project car 1986 Chrysler LeBaron convertible 2.2L Turbo II, modified A413

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85lebaront2

Re: 86 F150 5.0 running poorly

Administrator

In reply to this post by sdhorton

Well a 1991 is a much improved system from a 1986. Are you saying that an 06 French truck reminds you of a 1986 Ford? Ok, 1991 I think if you can find someone with a fair scan tool it may be able to read live data when running. Two of the major changes in addition to pin changes on the EEC are a speed input and a single duty cycle EGR control valve. You had me concerned when you posted a 3 digit code, 1986 only had 2 digit codes. 1990-up have a fuel pump module so no extra frame mounted pump.

That TPS does not need to be right at 1 volt, the EEC will read the value when cranking and set that as idle/closed throttle.

Shane, maybe these will help, they are from my AllData

Bill AKA "LOBO" Profile

sdhorton

RE: 86 F150 5.0 running poorly

Making some progress here, the EGR sensor is quite a ways out of whack and I am trying to figure out how the thermistor valve is supposed to be actuated. I have no vac to the EGR at idle like it is supposed to but I have no vacuum at higher rpm either. The red vac tube to the thermistor has vac but the valve is not opening. I can ground the wire on it and then it opens so I think the valve is OK I just don’t know what triggers it.

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Sent: Monday, April 6, 2020 3:50 PM
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Subject: Re: 86 F150 5.0 running poorly

Bill Profile

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sdhorton

RE: 86 F150 5.0 running poorly

In reply to this post by 85lebaront2

Well hell, I took someone elses word on the name of that component, it is not a thermactor it is the EGR vacuum regulator

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Sent: Monday, April 6, 2020 3:50 PM
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Subject: Re: 86 F150 5.0 running poorly

Bill Profile

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85lebaront2

RE: 86 F150 5.0 running poorly

Administrator

The thermactor is the air pump. EGR system I believe will only open after a certain speed is reached. The EGR and thermactor solenoid valves are all powered by the red wire that powers the injectors the brown/pink wire goes to pin #33 on the EEC after first passing through C101 which should be a round 8 pin (not all may be used) plug on the left inner fender. If it is working at all you should be able to feel it "hum" as it is a duty cycle valve which pulses.

Bill AKA "LOBO" Profile