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86 running rough

kaytor692

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having issues with my 86 B2 its over fueling like crazy ive replaced the fuel pressure regulator as ive had one fail before. i have also replaced the map sensor but the fuel pump just runs constantly. key on engine off fuel pump just runs and runs. what controls the pump? any help would be great thanks
 


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Uncle Gump

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I believe the fuel system has a return line... fuel pump should run constantly.

Have you checked your fuel pressure? If pressure is within specs... you may very well have an injector or two leaking. A quick way to check would be to monitor your fuel pressure gauge while running... then shut it off and see if the fuel pressure drops.

Edit... The fuel pump should power up momentarily with key on. It should restart when the engine fires up... then run constantly.
 

RonD

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Fuel pump should only run for 2 seconds with key on
Once engine is started, above 400 RPMs, it will be on full time

But fuel pump on full time(key on) shouldn't cause a running issue, so there are two issues here

All fuel injection computers have a "Clear Flooded engine" mode
Key on
Press gas pedal down to the floor and hold it down all the way
Crank engine
It should NOT start or fire, fuel injectors are OFF
This tests for leaking injectors

If computer "sees" WOT(wide open throttle) and 0 RPMs at the same time it will shut OFF injectors, so "Clear Flooded Engine" mode


Rich running and fuel pump on all the time can be a computer issue, pull out the computer and open it up
Have a look at the circuit board for corrosion, or "rust"
There will be 2 or 3 blue or black capacitors, these often fail/leak after 20+ years, but under $5 to fix
If you can solder or have a friend that can its very easy to replace these
 

kaytor692

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ok thanks for the info. you mean the computer in the passenger side kick panel right?
 

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kaytor692

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so swapped out the ecm with a good ish spare and the fuel pump issue is back to normal. i was reading on here that the 88 and newer ecm's are better is this a thing or should I just get another 86 ecm?
 

Paulos

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I have my doubts that the newer ECM would work on an '86. The '87 is wired very similar to the '88+ ECM's (and I know the '87 will work), but the '86 is different than the '87 also, even though the '87 has the EGR system like the '86.
The main difference between the '86 and newer ECM's (that I could see by the pin out sheet) is that the newer ECM's have a VSS (vehicle speed sensor). From what I remember the VSS is necessary for cruise control and the electronic transfer case shifter in the '87+ 4x4's. Would the newer ECM react negatively to not getting a signal from a VSS? I don't know. Maybe @RonD could help there.
The benefits to the newer ECM would be no more EGR or knock sensor troubles, and no more hot exhaust gases being sucked into the intake manifold.
Maybe someone in the forum that has done the upgrade on an '86 2.9 will chime in and share what they know.
 

RonD

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1988 manual computer in a 1986 with manual trans shouldn't matter, VSS was used for turning OD on and off, and if there is no Automatic software then I doubt it would set Code 27 - no VSS signal
If you had an automatic it would matter, 1988 auto could also have 2 solenoids, 1986 just 1

1988 computer would have spark timing for No EGR so that would be OK as well
 

kaytor692

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ok my B2 is an 86 manual trans manual transfer case. would it be better to go with the newer ecm or go with the og 86 ecm? the one in my truck is a reman anyways and they are pretty decent price wise on rockauto
 

RonD

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If you replace it then get the 1986
If the 1988 is working for you then keep it in
 

kaytor692

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got the old girl back up and running with a good used ecm and a fresh set of plugs. thanks for the help fellas much appreciated
 

kaytor692

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anyone by chance no the size of the bolts in the ignition module on the back of the distributor ?
 

Paulos

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I've had one of these for many years. It's 5.5mm.
 

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