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'87 2.6l running rough - seems electrical #1105909 02/08/21 10:26 PM
Joined: Nov 2013
Posts: 94
G
GrantCee Offline OP
Getting the Wheeling Fever
Having a sudden problem with my '87 2.6l with a Weber conversion.

A couple of mornings ago it suddenly started up rough — sounds like it's misfiring on one cylinder, but it comes and goes. As it warms will idle fine one minute, then the next it will start missing. Sometimes it misses at idle but clears up when the throttle is increased, sometimes the opposite. It was perfectly fine the day before.

As part of my troubleshooting, I found one of the spark plug wires had slipped out of its holder and was resting on the belt tension adjuster. It had worn to the point that you can see scorch marks on the adjuster frame where the wire was clearly shorting. I thought that HAD to be the problem, so I replaced the wires, cap & rotor. Also, the timing appears good (hasn't changed). The problem persists.

I've never encountered a bad coil, so I don't know whether these symptoms match a failing coil.

Any other ideas are welcome.

Last edited by GrantCee; 02/08/21 10:44 PM.

1987 Montero SWB, 2.6L, 5spd
Weber conversion
2-valve head from Engine Machine Service
"4G54 FTW!"
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Re: '87 2.6l running rough - seems electrical [Re: GrantCee] #1105910 02/09/21 03:20 AM
Joined: Feb 2005
Posts: 7,390
rxinhed Offline
Trail Leader
*****
Check the resistance across the ballast? How are the ECU bits? Any water coming into the bottom of the carb?

Re: '87 2.6l running rough - seems electrical [Re: rxinhed] #1105915 02/09/21 06:55 PM
Joined: Nov 2013
Posts: 94
G
GrantCee Offline OP
Getting the Wheeling Fever
Originally Posted by rxinhed
Check the resistance across the ballast?


Finally found Vol 2 of my FSM (it had fallen down behind the bench) and tested the coil and resistor:

Ballast: 1.8 (which is out of spec - high)
Primary: 1.5 (which is also out of spec, high)
Secondary: 15 (which is on the low side of spec, but "in")

If my understanding of the operation is correct, the high ballast resistance would result in lowered voltage sent to the primary, and the high primary resistance would result in lowered inductance to the secondary — the combination of which would produce a weak spark. True?

Quote

How are the ECU bits?


Removed when the Weber was installed.

Quote

Any water coming into the bottom of the carb?


Not that I can see. Also, the plugs are all dry and have a light coating of ash (i.e., no signs of being steam-cleaned.)

Last edited by GrantCee; 02/09/21 11:32 PM.

1987 Montero SWB, 2.6L, 5spd
Weber conversion
2-valve head from Engine Machine Service
"4G54 FTW!"
Re: '87 2.6l running rough - seems electrical [Re: GrantCee] #1105916 02/10/21 04:20 AM
Joined: Feb 2005
Posts: 7,390
rxinhed Offline
Trail Leader
*****
Weak spark, yes, my understanding. What heat range plugs?

Re: '87 2.6l running rough - seems electrical [Re: rxinhed] #1105917 02/10/21 04:46 AM
Joined: Nov 2013
Posts: 94
G
GrantCee Offline OP
Getting the Wheeling Fever
I haven't double-checked, but I think I went with the FSM's recommendation of NGK BPR6-ES11. From NGK's chart, they're on the hot end of the "normal" range.

A new coil and resistor are inbound.

Last edited by GrantCee; 02/10/21 04:48 AM.

1987 Montero SWB, 2.6L, 5spd
Weber conversion
2-valve head from Engine Machine Service
"4G54 FTW!"
Re: '87 2.6l running rough - seems electrical [Re: GrantCee] #1105918 02/10/21 06:24 AM
Joined: Feb 2005
Posts: 7,390
rxinhed Offline
Trail Leader
*****
Sage parts purchase, anyway.

Re: '87 2.6l running rough - seems electrical [Re: GrantCee] #1105932 02/16/21 04:55 AM
Joined: Dec 2007
Posts: 2,303
Mudraider Online Content
Body Damage is Cool
Originally Posted by GrantCee
I haven't double-checked, but I think I went with the FSM's recommendation of NGK BPR6-ES11. From NGK's chart, they're on the hot end of the "normal" range.

A new coil and resistor are inbound.

So did those parts help?


89 SWB, V-6 5SPD, OME Shocks, 16.5X37's, 2"BL, SR axle, Gen2 brakes, Lincoln w/Superwinch
Re: '87 2.6l running rough - seems electrical [Re: Mudraider] #1105956 02/25/21 09:21 PM
Joined: Nov 2013
Posts: 94
G
GrantCee Offline OP
Getting the Wheeling Fever
Sorry to disappear like that, folks, but we had an ice storm that took us offline for two weeks! We also suffered without power for 6 days, but I'm here to tell you not having 'net access was worse!

Originally Posted by Mudraider
So did those parts help?


No, the problem persists. I did some more diagnostic work; I hooked up a timing light on each of the plug wires, pointed it at a wall, and watched the pulses. I can see the misses, and they occur on all cylinders (though they seem to happen more often on #2 and #3). With the replaced coil and wires, this suggests that the igniter is bad since it's the only thing in the circuit which hasn't been replaced.

Unfortunately, the FSM has no procedure to check the igniter, and my impression has always been that an igniter either works or it doesn't; I've never heard of one failing intermittently. Just in case, I have a new one on the way, but would appreciate any insights on this.

Last edited by GrantCee; 02/26/21 12:26 AM.

1987 Montero SWB, 2.6L, 5spd
Weber conversion
2-valve head from Engine Machine Service
"4G54 FTW!"
Re: '87 2.6l running rough - seems electrical [Re: GrantCee] #1105958 02/28/21 02:52 AM
Joined: Feb 2005
Posts: 7,390
rxinhed Offline
Trail Leader
*****
The electromagnet that makes up the igniter, if it breaks through thermal cycling, will create a bunch of magnetic fields that create the misfire. This alone is diagnostic. When I worked on the Honda cars, this was a common thing to replace and how we found the issue.

Last edited by rxinhed; 02/28/21 02:52 AM.
Re: '87 2.6l running rough - seems electrical [Re: GrantCee] #1105961 02/28/21 07:30 PM
Joined: Nov 2013
Posts: 94
G
GrantCee Offline OP
Getting the Wheeling Fever
Well, got the new igniter installed...first thing I noticed is that there was no ground wire on the old one, as shown in the FSM. I need to make one and install it.

Other than that, the engine idles better now — but misfires BADLY as soon as a load is applied. It will barely move out of the garage.

Worried about a blown head gasket, I checked the compression on all cylinders, and they're above minimum spec (160-175psi).

I'm at my wit's end trying to figure out how a perfectly running engine could suddenly develop this problem.

Wondering if the centrifugal advance has failed (the vacuum advance is definitely working.) The inside of the distributor has some dirt and what appears to be a very small amount of powdered rust.

(My wife reminded me of something that might aid diagnosis: the night before these symptoms appeared, we'd made a short run to the post office for our mail — 5 miles total round trip — and when I shut the engine down it dieseled. Not a smooth run-on revolution or two, but repeated rough revolutions. I turned the key back on, let the engine run for 30 seconds or so, and it shut down normally. Seemed fine, but the next morning the problem showed up. Related?)


Last edited by GrantCee; 02/28/21 07:56 PM.

1987 Montero SWB, 2.6L, 5spd
Weber conversion
2-valve head from Engine Machine Service
"4G54 FTW!"
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