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Erratic Idle and bucking

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TheWeldingFords

Erratic Idle and bucking

Hi Y'all,

Recently while driving around when I come to a stop light the idle is jumping up and down from 500 rpm up to 1200 rpm and it just repeats that for a bit and then suddenly stops and holds at 1000 rpm for a bit and then goes back to surging.

The second problem I have that I believe might be related is that when accelerating 1/3rd of the pedal or more it bucks and doesn't accelerate past that point in that gear typically happens around 3500 rpm and at some points if you floor it like that it might backfire(only happened twice to me) the other problem I notice is that its intermittent so sometimes I can use every bit of rpm i can get out of the engine and then the next time I go to do a hard pull and accelerate it'll buck.

Any info on what to check this time would be helpful since I have 30 days before I drive 3000 miles to Alaska

I replaced the TPS today with a Standard one just to see if it would help and it has not changed anything. I also upgraded to a PMGR starter today because when I went to drive back home from Orielly's my starter crapped out in the parking lot and decided today was the day to upgrade got a $350 starter for $60 (pretty happy with it, super quiet and powerful. Only problem I noticed is it hangs out for half a second after the truck starts and it makes a little bit of noise but goes away fairly quickly. Would a shim possibly fix this?)

Alex

Daisy: 1986 F250 XLT 5.0L EFI 4x4 Manual

Roseanne: 1993 Ford Ranger 2.3L 4cyl Rwd Manual

ArdWrknTrk

Re: Erratic Idle and bucking

Administrator

Alex, Have you got the solenoid jumpered, or did you run a trigger wire from the fender relay output to your starter and move the cable to be powered all the time?

When your truck is bucking and backfiring have you checked to see if the ignition coil is really hot?
Because those symptoms sound like a failing coil.

I hope you can get Daisy running right before the big road trip.

Jim,
Lil'Red is a '87 F250 HD, 4.10's, 1356 4x4, Zf-5, 3G, PMGR, Saginaw PS, desmogged with a Holley 80508 and Performer intake.
Too much other stuff to mention.

TheWeldingFords

Re: Erratic Idle and bucking

I just drove to work when I had the problem again and I felt the coil and it didn't feel hot just a bit warm from the engine bay heat.

Alex

Daisy: 1986 F250 XLT 5.0L EFI 4x4 Manual

Roseanne: 1993 Ford Ranger 2.3L 4cyl Rwd Manual

ArdWrknTrk

Re: Erratic Idle and bucking

Administrator

Hmmm
I suppose it's a step that you can eliminate the coil itself.

The problem does seem more spark related that fuel related, though I'm no expert in these early EFI systems.
Let's see what others have to suggest.

Jim,
Lil'Red is a '87 F250 HD, 4.10's, 1356 4x4, Zf-5, 3G, PMGR, Saginaw PS, desmogged with a Holley 80508 and Performer intake.
Too much other stuff to mention.

Gary Lewis

Re: Erratic Idle and bucking

Administrator

Yes, it sounds like ignition to me as well. And I'd guess it is the TFI module. The '86 EVTM shows the EEC controls the TFI module, and those are a known failure point during these years as most were mounted to the distributor. Later Ford moved them to the fender where they didn't get as hot, but wonky running or not running at all when hot is one of their symptoms.

Gary, AKA "Gary fellow": Profile

Dad's: '81 F150 Ranger XLT 4x4: Down for restomod: Full-roller "stroked 351M" w/Trick Flow heads & intake, EEC-V SEFI/E4OD/3.50 gears w/Kevlar clutches
Blue: 2015 F150 Platinum 4x4 SuperCrew wearing Blue Jeans & sporting a 3.5L EB & Max Tow
Big Blue: 1985 F250HD 4x4: 460/ZF5/3.55's, D60 w/Ox locker & 10.25 Sterling/Trutrac, Blue Top & Borgeson, & EEC-V MAF/SEFI

81-F150-Explorer

Re: Erratic Idle and bucking

In reply to this post by ArdWrknTrk

Some suggestions ...

----------------------------------

The TFI-IV Ignition Module?

Located on the distributor, and is prone for overheating.

----------------------------------

The Idle Air Controller (IAC) ?

---------------------------------

Sticking EGR Valve?

--------------------------------

Severe Vacuum Leaks?

-------------------------------

PCV Valve malfunction or leak?

==================

The EEC-IV / TFI-IV has a self Diagnostic routine. Both Key On, Engine off, and Running. First thing I would do is check the Self Diagnostic for codes to help narrow things down.

Truck: 1981 F-150 Explorer / Engine: 300-6 California MCU Feedback System / Trans: T-18 - 4 speed / 2.75 Ford Rear Axle Open Diff.

81-F150-Explorer

Re: Erratic Idle and bucking

In reply to this post by Gary Lewis

Great minds etc...

Truck: 1981 F-150 Explorer / Engine: 300-6 California MCU Feedback System / Trans: T-18 - 4 speed / 2.75 Ford Rear Axle Open Diff.

Gary Lewis

Re: Erratic Idle and bucking

Administrator

81-F150-Explorer wrote

Great minds etc...

I'll take that as a compliment.

Gary, AKA "Gary fellow": Profile

TheWeldingFords

Re: Erratic Idle and bucking

In reply to this post by 81-F150-Explorer

The IACV is about a month old, I haven't looked into the tfi module, I was thinking it might be related to that as I've read through the forum and mine is still distributor mounted. Any idea when I can get a kit to move it to the fender? Is it a decently easy job? I'm gonna pull up to the mechanic later after work and see what they say also, I'm gonna check timing again too and verify that it didn't somehow move on me.

Alex

Daisy: 1986 F250 XLT 5.0L EFI 4x4 Manual

Roseanne: 1993 Ford Ranger 2.3L 4cyl Rwd Manual

ArdWrknTrk

Re: Erratic Idle and bucking

Administrator

The two places I know that used to offer TFI relocation kits/harnesses are Mcully Racing (the 5.0l Miata folks) and Fat Foxx.

Jim,
Lil'Red is a '87 F250 HD, 4.10's, 1356 4x4, Zf-5, 3G, PMGR, Saginaw PS, desmogged with a Holley 80508 and Performer intake.
Too much other stuff to mention.

TheWeldingFords

Re: Erratic Idle and bucking

How hard do you think it would be to make my own because it just seems like a few connectors, wire, a new module, and an aluminum heatsink

Alex

Daisy: 1986 F250 XLT 5.0L EFI 4x4 Manual

Roseanne: 1993 Ford Ranger 2.3L 4cyl Rwd Manual

Gsmblue

Re: Erratic Idle and bucking

Jfyi: When i replaced my TF
I I got a bad one and it threw me for a bit, changing it for a motorcraft one cured the issue.

1985.5 F-150 XL Explorer standard cab 5.0 EFI AOD 4x4
Daily Driver. We call her Eunice the Ute.

1982 Bronco XLT Lariat 351W AOD 4x4
Code name Esperanza, or Espy to her friends. Please see my Project thread for the blow by blow.

1984 F-350 XL Centurion crew cab 460 T19 4x4
"Eylza Dual-little"

81-F150-Explorer

Re: Erratic Idle and bucking

Gsmblue wrote

Jfyi: When i replaced my TF
I I got a bad one and it threw me for a bit, changing it for a motorcraft one cured the issue.

Very good point about motorcraft parts.

Even with the Duraspark II ignition modules, the Motorcraft ones are worth the extra dollars.

When warmed up, my 1981 with a Motorcraft DS-II, will start with the first crank of the starter. Something an aftermarket DS-II will not allow you to do. I know from experience.

Truck: 1981 F-150 Explorer / Engine: 300-6 California MCU Feedback System / Trans: T-18 - 4 speed / 2.75 Ford Rear Axle Open Diff.

Gary Lewis

Re: Erratic Idle and bucking

Administrator

In reply to this post by Gsmblue

I remember seeing some things regarding remoting a TFI module on here, so have done some searching and found this hits:

TFI Ignition Rehab: I think this is what you are looking for.

https://forum.garysgaragemahal.com/Help-Me-With-TSB-Info-tp97717p97779.html

Stall/No Start TSB

Gary, AKA "Gary fellow": Profile

ArdWrknTrk

Re: Erratic Idle and bucking

Administrator

In reply to this post by TheWeldingFords

It's a few connectors, some wire and a heatsink but you need a blank-off plate and the harness should be shielded.

IDK how you feel about that but in my mind it would be much easier to get the harness that someone else has already done all the trouble shooting.
Probably the same $$$ in the end.

Jim,
Lil'Red is a '87 F250 HD, 4.10's, 1356 4x4, Zf-5, 3G, PMGR, Saginaw PS, desmogged with a Holley 80508 and Performer intake.
Too much other stuff to mention.

TheWeldingFords

Re: Erratic Idle and bucking

Well I just got back from the mechanic and they said injectors when he pulled the plug on the cylinder 5 injector it had little to no change in idle but when I pulled the plug on cylinder 6 it bogged down.

Any recommended brands of injectors?

Alex

Daisy: 1986 F250 XLT 5.0L EFI 4x4 Manual

Roseanne: 1993 Ford Ranger 2.3L 4cyl Rwd Manual

Gary Lewis

Re: Erratic Idle and bucking

Administrator

I'm running Accel injectors. There are several on here that don't like that brand, but my engine builder (Scotty the Mad Porter) recommended them and they've worked fine.

Gary, AKA "Gary fellow": Profile

TheWeldingFords

Re: Erratic Idle and bucking

I just replaced all 8 with standard injectors and the running issue is still there but it fixed the tiniest of misfires and runs a tad bit smoother.

I gave in and bought a TFI module but I'll install it in the morning because the whole engine bay is toasty.

Alex

Daisy: 1986 F250 XLT 5.0L EFI 4x4 Manual

Roseanne: 1993 Ford Ranger 2.3L 4cyl Rwd Manual

Gary Lewis

Re: Erratic Idle and bucking

Administrator

Hope the TFI module does it.

Gary, AKA "Gary fellow": Profile

81-F150-Explorer

Re: Erratic Idle and bucking

In reply to this post by TheWeldingFords

Number 5 Cylinder is the farthest cylinder away from the fuel pump isn't it?

If the TFI module does not fix it, I'd check the fuel pressure for weak flow.

When was the last time you changed the fuel filter? etc . . .

Truck: 1981 F-150 Explorer / Engine: 300-6 California MCU Feedback System / Trans: T-18 - 4 speed / 2.75 Ford Rear Axle Open Diff.

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