Please help. I have an 86 Ford F150 , 302 EFI, Automatic. I have been working on this truck for a while and can not figure out why it cuts out on me. I thought I had it fixed and now it is back. I have replaced many parts, most recently the vacuum modulator because of fluid in the vacuum line. Please help me fix this.

135

Asked by Sep 03, 2013 at 08:25 PM about the 1986 Ford F-150 XL Standard Cab LB

Question type: Maintenance & Repair

46 Answers

210,865

When does it cut out? Engine Hot or cold or both?

6 out of 6 people think this is helpful.
135

It cuts out when the engine is at operating temperature. It has been a while since it has cut out until I replaced the vacuum modulator. Is there anyway these ar connected or is it coincidental?

1 out of 1 people think this is helpful.

do you mean the fuel pressure regulator?

1 out of 1 people think this is helpful.
135

No. I did replace the pressure regulator too but I replaced the vacuum modulator on the transmission.

1 out of 1 people think this is helpful.
78,545

What have you replaced so far? Does it completely stall out or give a kick but stays running?

4 out of 4 people think this is helpful.

I can remember replacing many ignition modules on these....please check for reliable spark...~

3 out of 3 people think this is helpful.

look at the distributor cap to make sure it isn't cracked~

3 out of 3 people think this is helpful.
135

I have replaced the distributor cap, rotor, IAC,TPS,EGRvalve and position sensor, I recently discovered I have the wrong position sensor, vacuum modulator,PCV,fuel pumps, fuel filter, injectors,pressure regulator,spark plugs,ECT sensor,air filter, . Yesterday was the worst is has been. It tried to cut out twice but recovered and then completely cut out on me 5 times on a 30 mile ride. Judge Roy: I have not done too much with the ignition parts. I had a friend helping me out and he seemed to think it was a vacuum leak so I kind of stayed on that track.

3 out of 3 people think this is helpful.
210,865

Look for the vacuum leak. Did you scan for codes with an old OBDi box scanner or using the sweeps of the needle on a voltmeter? This link might help some....http://www.stangnet.com/mustang-forums/threads/help-me-create-the-surging-idle-checklist.698148/

2 out of 2 people think this is helpful.

...well...you need reliable spark...vacuum leak or not....you still need spark...there are three components inside the distributor (make you a mechanic if you can change this one out) on the side of the distributor and another main unit~ If you've got reliable spark wouldn't bother with these~

2 out of 2 people think this is helpful.
135

Hey Tom I get two codes, one of which I am going to fix tomorrow. I get a out of range on the EGR position sensor and a main fuel pump circuit failure. I can hear the pump run so I am going to check for bad ground this weekend. Judge Roy: What is the best way to check for a good spark? One thing I should have mentioned is that 97% of the time these things happen is while in drive. If I hear it starting to run rough or stumble and put it in neutral or park the idle usually speeds up and straightens out.

4 out of 4 people think this is helpful.

Please do not have a little kid put the high-voltage wire on his tongue~ unscrew a sparkplug...put the wire on one end a jumper cable on it to hold it+proper chassis ground or battery....turn the key and wait for the spark....trouble, check for 12 Volts at the low voltage side of the coil~ or packs~

3 out of 3 people think this is helpful.
135

Darn. My first test was going to include a little kid. LOL I will give this a try.

1986 was a very good year....the ignition system is a pain whatever with it's three parts of glory....the ignition module, the distributor module. and sadly the resolver which requires removal of the distributor which is perched on a helical spur gear that changes position when you engage it...crummy design, they should have put a simple D ring like volkswagen's bosch distributors do, but WE are Americans dammit!----so if you've got to do this business of pin-punch the roll-pin out of the spur gear at the base of the distributor to change out the resolver....would suggest; just get another distributor~! rockauto.com summitracing.com.....enough is enough already...the hours I spent as a Sunday mechanic tryin' to figure this all out was hardly worth the hours we made the customer pay~

1 out of 1 people think this is helpful.
135

I have been chasing a vacuum leak that I don't believe ever existed. The truck ran pretty good when we first bought it and it has been downhill from there. I have replaced so many parts it is getting very old. I have increased the fuel economy drastically. I do not have the truck here so I will test the spark tomorrow. I will keep you posted so you can share in my pain. LOL

1 out of 1 people think this is helpful.

buy the expensive silicone replacement vacuum lines...you can rest assured they will NOT crack and leak that way~ one at a time with a scissors will take a lazy afternoon out of your weekend~

3 out of 3 people think this is helpful.
135

Thanks. Until I get this thing running good and reliably I won't have a lazy afternoon.

2 out of 2 people think this is helpful.
1,125

I encountered a similar problem on a 1979 F150. Finally after replacing almost everything in the ignition system, as a last resort, I replaced the ignition switch ( mounted on top of steering column just behind dash) problem solved. Won't guarantee it, but it's just one more thing to try.

1 out of 1 people think this is helpful.
135

Thank you for the suggestion Markand Norma. Judge Roy, I checked the spark. I took a plug out , put the boot in the clamp of jumper cables. The other clamp was hanging too close to the fan so I clamped it on to the frame of the truck just above the radiator. I held the jumper cable with the spark plug and plug boot close to the manifold and got a big zap. I tried again with pliers and the spark is very strong and a bright orange. I am wondering if my coil is energizing the truck. I checked the coil and it is very loose in the bracket. It just flops around. What are your thoughts?

1 out of 1 people think this is helpful.
1,125

If you have an old inner tube you could wrap a piece of that around the coil and that would isolate it and answer your question.

50

Fellow, I have a1986 ford f150 fuel injected 5.0 that I am restoring and had the same issue. replaced complete dist., fuel pumps, tune up, relays, all vac. hoses, TPS, idle air control valve, fuel tank, EGR, timing chains, engine computer, fuel pump and ecm relays, .injectors, etc.. to find out overall that the pigtail to distributer was bad!! Kevin

4 out of 4 people think this is helpful.
50

also forgot to mention, there is a paper cartridge fuel filter inside the frame of the truck, inside the little black plastic filter housing that will make truck run bad, from shut down to popping like a engine misfire! the replacement filter is about $7.00 at auto parts. fuel resovoir filter. pugh

1 out of 1 people think this is helpful.
10

I also have this same problem on a 94 150 EFI my have turned out the the pipe lead from the bottom of the EGR have broke in two. when the truck shuts off does it act like its flooded? if so most like its the EGR or the piping to the EGR

50

I have an 86 ad well with a 302 efi, ran into the same issue, what I did in mine was to bypass the fuel selector valve disabling the second tank. Worked like a charm now I can drive my truck again. the only way I get the same symptoms is when I'm low on fuel. Also found a bent fuel line under the truck that might have added to the problem

4 out of 4 people think this is helpful.
90

also check idle air motor they get carbon up and stick

1 out of 1 people think this is helpful.
10

From 1970's to 2000's with a carbureto .....You people owe me because I'm a Ford Fool... The problem is the Carburetor Accelerator Pump Diaphragm.. That sucker pumps the gas on the carburetor.... The part cost $10.. wow send the check to (ericrossconsultant@gmail.com) http://images.apwcontent.com/is/image/Autos/rb90082_is? wid=250&hei=250&DefaultImage=noimage[/url]

1 out of 1 people think this is helpful.
78,545

Eric this post was in 2013 for an EFI Truck it has no accelerator pump.

3 out of 3 people think this is helpful.

for a fraction of the money you have spent you could buy an obd1 code reader. Its well worth the investment and chances are it will be your best friend when it comes to your pick up. I had what sounds like the same problem you have(or hopefully had by this time) on my 87 f150 302 efi and the code reader said it was the map sensor. Changed it out and all ok. Also the vacuum line running from the map sensor to the manifold may be of the old plastic variety that has a tendency to crack. If it cracks the vacuum leak that it creates will be minor compared to the problems the map sensor will create due to bad signals sent to the pcm.

Have an 86 with EFI. Now I can say I have checked for codes and have none, replaced every sensor except the knock sensor which I understand is not available and is pretty reliable and not a possible problem. Replaced all fuel pumps and regulator. Pulled and tested all injectors then refurbished with new seals and filters. Thought maybe after all this it was a computer problem. Replaced the ECM with another from another 86. same issue. Driving at cruse, just shuts off. press on the accelerator and it kicks back in. then does it again. This is at operating temp. Also if I leave it in the driveway and idling at operating temp it will just shut off. Oh and have tried three different TPS and three different MAP sensors. Im totally at a loss lol!

78,545

Have you replaced the Ignition module and distributor pickup coil?

1 out of 1 people think this is helpful.
50

Check out my post from earlier I had the same issue. I bypassed the fuel selector valve and it worked for me

1 out of 1 people think this is helpful.

Hey and thanks! Yes.replaced the whole distributor including TFI, coil, cap, wires and plugs. Removed the old ford fuel selector valve and installed a tank selector solenoid. Fuel pressure is within spec 35 PSI at idle with the new high pressure pump. Old High pressure pump was also within spec at about 30 PSI.

78,545

Have you also checked the lift pumps in the tanks?

Yes, both new with new pickup filters, rear tank is new and front tank was flushed. The reason this issue is so frustrating is because I started with a barely running mess about 5 years ago, Previous owner had no idea about fuel injection. My original intent was to convert it to a carburetor. Wiring was hacked and things were bypassed. Started out fixing the obvious issues and started finding myself throwing parts at it , sort of hit and miss. Picked up an OBD reader and pulled codes. That pointed me in the right direction. Got it idling better and mileage was up. Still had some issues but I began to trust it to drive fairly regularly. Out of the blue this issue started to appear. Just one day the truck shut off. Started right back up. Only happened now and then for months and I started to suspect grounding issues, redid all the ECU grounds with no improvement but now its multiple times every trip. Codes tell me nothing. Its just like I turned off the key except the ignition is still live and the tach is still registering as the rpms drop. So this tells me the ignition switch is not at fault. Started thinking it was fuel so went through the whole fuel system, pumps, switching valve, regulator, injectors, Injector relay, inspect wiring loom (again). When it stalls out the pressure remains up and the pumps keep running until the engine stops turning as designed. Started thinking it must be electrical so replaced the distributor tested TPS again and Map sensor again . New coil, New wires. Anyway have run out of things to replace. So chasing the stalling issue because its fairly unpredictable and becoming a safety issue. Just looking for ideas but thing I just have to step back and start over, Sure it will be ridiculous when I finally do find it .

78,545

Back in the days when I worked at A Ford dealership, I ran across a pickup that for no apparent reason would just up and die, everyone in the shop had a go at this rig, no one could find the problem, one day I got lucky, I had the breakout box hooked and was driving it and noticed that the light that indicated key power was there went off and it quit, then the red light came right back on and it started up, any way I found if I tapped on the EEC power relay it would drop out then reconnect, replaced the relay and it was cured, have you tested all the main power relays?

Great suggestion but yes I did replace with a new relay even though the old one tested out ok. Also changed out the main one in the engine bay. But at this point i am 99% sure its electrical because when it dies its clean, no sputtering or jerking or loss of power. Its just as if the key was turned off. Am at the point that I think i'm going to start tapping into the various 12V+ circuits from the ecu with my meter and just drive as you did. Hopefully will see if there is an intermittent break when it stalls out. If I don't find out anything from this I think i'll pull the harness again and strip off the tape and plastic do a visual and meter test from the ECU connector to the various end connectors. But thanks for the suggestion it would make a lot of sense. The one thing that is interesting is the Tach still is reading the output from the distributor pickup when it quits while i'm driving and coasting before it kicks back in. This indicates (to me anyway) that the distributor circuits are still powered.

78,545

That sounds like your on the right track. Just 1 more thought when was the last time the ignition switch was replaced, as these are a known high fail item.

Thanks Yup I did wonder about the switch. Best I can tell its working right and not cutting out. Its not new and one of the few parts I have not replaced. I did test it a couple of years ago when I replaced the column with a non-tilt one from the pull a part. Old tilt one was shot and needs rebuilding. The replacement had a fairly new switch on it already so I used it. I went out today and pulled codes once more and put a test light on the 12V circuit powering the ecu. It once more died in the driveway and the power never was cut to the ecu. I'm leaning towards a bad ECU even though I have 2 and both are acting the same. Tomorrow i'm going to the junk yard to see if I can find another harness and perhaps another ECU. Just cant find anything obvious wrong with the wiring as far as damage goes. But it is 30 years old. Really close to converting to a carb setup. But thanks for the input and of course I'll post what I eventually find.

I have a 1987 F150 with 5.0L that does this also. I haven't even begun to investigate what causes my truck to want to stumble or stall out when it gets warm, yet. I'll start it and drive about 1.5 miles and when I go to stop it will try to die. Restart it, punch the accelerator and it will usually be ok after that. It sat for quite a few years not being driven before I bought it, so despite bleeding the brakes, I still have a soft pedal also. I'm hoping this column of answers will help as I don't have the resources to replace every single part there is!

78,545

Some things that are must do's if a rig has sat any length of time, put a can of SeaFoam in the fuel tank, clean the throttle body and check the minimum air rate adjustment, give it a complete tune up, plugs cap rotor wires filters etc. then check for any stored engine trouble codes and repair them. Now on the brakes, sitting is one of the most destructive things for a brake system, water will settle in the fluid and start putting surfaces needed for a good hydraulic seal, so chances are very high that you will wind up replacing the master cylinder and wheel cylinders and calipers and brake hoses before you get it to operate at full potential. HTH

Forgot to add, it does have a new Master Cylinder. Maybe the booster or proportional valve?

78,545

If it was the booster the pedal would be hard to push and you might hear a vacuum leak every time you stepped on the pedal. If it is a new master cylinder was it properly bench bleed before it was installed?

78,545

A proportion valve the brake light would be on and possibly one end or the other would not have any brakes. Also make sure the rear shoes are adjusted properly and the auto adjusters are not froze.

10

i have a 89 f 150 302 5.0l efi with simliar problems, from first start run's about 15 minuets and die's. restart run's 15 minutes then die's. on the third try sometimes ruffer to start with and with out acclerated in park or driving ( driving distance of about 200 yards) it starts running like crap. and poping sound in the intake. i have replaced.. ICM,Fuel Filter, plugs and wire's have had timing set and checked 4 times. also coil replaced .and destrubuter and cap and rotter button.. very limited resource do to house fire. and my truck craped out on the same day. Any help would be useful.

10

also guy's i do have a little familuer fillings with one starting issue with a 86 f 150 i had the linking rod in the collum, look's like a hook in a way are bad for breaking and cause a dieing issue. part is normally 12 to 15 dollars at Napa auto parts. here is a link to which it looks like and resonable cost. also for cheaper part price's cheeck out www.partsgeek.com https://www.summitracing.com/parts/rnb-83280? seid=srese1&cm_mmc=pla-google-_-shopping-_-srese1-_- dorman&gclid=CJeT9pni2dACFUS2wAodO7ILkw

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10

to make it easier here is a pic hopefully it show's up

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