Backfiring Badly During Attempt to Get My '84 FJ60 Running After Sitting for a Few Years (1 Viewer)

4Cruisers

Supporting Vendor
SILVER Star
Joined
Apr 2, 2015
Messages
6,443
I'm trying to get my stock '84 FJ60 (with ~181,500 miles) running again after sitting in the garage for a few years. Back then I swapped in a rebuilt carburetor, changed the spark plugs, did an oil and filter change, replaced the fuel pump and fuel filter, and did a warm valve adjustment. After all that work it was running as a good 2F should, it sounded like a well-oiled sewing machine.

Yesterday i drained the fuel tank, it had a little over a gallon of old gasoline in it. I added a few gallons of fresh 86 octane gasoline. I blew compressed air back through to the fuel tank and checked the fuel pump, it's working fine. I was running what was left of the old fuel through the system and into a coffee can. I could get it to start briefly by pouring a little fresh fuel down the carburetor primary bore, but couldn't keep it running.

Today I replaced the fuel filter again and added a few ounces of Sea Foam to the fuel tank. And I added about a gallon of 91 octane gasoline.

After a dozen or so attempts I got it to run roughly while feathering the accelerator pedal, but it's backfiring badly. Could the Sea Foam cause backfiring? I was thinking it might be a restriction in the exhaust, maybe a packrat nest?

What should I try next? I think the fresh fuel and Sea Foam are getting me a lot closer, but am running out of ideas.
 

cruisermatt

Un-manufacturable
Supporting Vendor
SILVER Star
Joined
Jul 22, 2012
Messages
9,681
Location
Orlando Florida
Check for corrosion under the distributor cap. Make sure the contacts on the cap and rotor are nice and clean.

How long has it been since it was running correctly?
 

4Cruisers

Supporting Vendor
SILVER Star
Joined
Apr 2, 2015
Messages
6,443
Three years or so. I’ll check the distributor in the morning.
 

Dr. John

SILVER Star
Joined
Oct 27, 2005
Messages
222
Location
West Columbia, SC
What Cruisermatt said. Cracked/split vacuum lines? The Seafoam won't cause backfiring but might loosen up a lot of crud in the tank. Might have to just keep urging it on until everything clears.
 

g-man

SILVER Star
Joined
Sep 5, 2006
Messages
3,025
Location
Charlottesville VA
Disconnect the fuel filter and put the line in a 1 gallon container of fresh fuel. Have someone hold it while you start the truck. Just a way to rule out trash/water coming from the tank/lines.
 

g-man

SILVER Star
Joined
Sep 5, 2006
Messages
3,025
Location
Charlottesville VA
Double check the firing order on the plugs...ie they are connected to the right cylinder, make sure each plug has spark.

When you checked the fuel pump ...did you disconnect the fuel line at the carb to see fuel coming out? Did you catch it in a mason jar and see if there was water or trash settling out of it?
 

rrv333

SILVER Star
Joined
May 2, 2011
Messages
1,605
Location
Weatherford, Texas
Check for corrosion under the distributor cap. Make sure the contacts on the cap and rotor are nice and clean.

How long has it been since it was running correctly?

This ^ also check for cracks. Had an old 74 Cheby that was doing the same thing and it had developed a hairline crack that was invisible, if you just glanced at the cap. Had to take the cap off and really study it under good lighting to find the crack.
 

4Cruisers

Supporting Vendor
SILVER Star
Joined
Apr 2, 2015
Messages
6,443
Thanks for all the suggestions. The distributor, cap, and wires are all good. I was missing a cap on a tee in the PCV hose. I got it to start and run in its own without any choke, idles nice and smooth at just under 600 rpm. Took it out for a drive around the neighborhood, no more than 25 mph. By the time we got back home about 10 minutes later it had a low knock and the oil pressure was down to about 24 psi. I let it cool down for a while then started it up again. Idled smoothly for a while until it warmed up again, then the knock reappeared and the oil pressure was back down to the low 20s.

I’ll try to post the video I took.
 

g-man

SILVER Star
Joined
Sep 5, 2006
Messages
3,025
Location
Charlottesville VA
I guess a leak from the pcv would be a huge vacuum leak. sorry to hear about the knock and low psi. Both those together doesn't sound promising. I had a stuck lifter when I bought mine and it knocked for a few days but loosened up on its own. Never low oil though. I guess a compression check would be next. When you drove you only did 25mph because? Can you get the rpms to 2k? No power loss? Is there a chance the oil in the hose to the aftermarket oil pressure gauge is clogged? Is the stock oil gauge showing low as well?
 

4Cruisers

Supporting Vendor
SILVER Star
Joined
Apr 2, 2015
Messages
6,443
25 mph because I never left the residential area. I’ll try again along the US 95 frontage road at higher rpms. And I’ll check the aftermarket oil pressure tube for obstructions and see what the stock gauge shows.
 

4Cruisers

Supporting Vendor
SILVER Star
Joined
Apr 2, 2015
Messages
6,443
OK, I took it out on US 95 through town at the 45 mph speed limit. No knocking while running, had it above 2,600 rpm a few times. If I keep the idle rpms at 650 with the choke pulled out the oil pressure never drops below 40 psi, and the low rumbling (not really a knock) is pretty much gone. Tomorrow morning I’ll adjust the idle mixture and idle speed - I think the mixture is too rich, causing some of the roughness while running. A bit of tune-up will help to see what, if anything, is going on.
 
Joined
Jul 30, 2012
Messages
432
Location
Albuquerque NM
OK, I took it out on US 95 through town at the 45 mph speed limit. No knocking while running, had it above 2,600 rpm a few times. If I keep the idle rpms at 650 with the choke pulled out the oil pressure never drops below 40 psi, and the low rumbling (not really a knock) is pretty much gone. Tomorrow morning I’ll adjust the idle mixture and idle speed - I think the mixture is too rich, causing some of the roughness while running. A bit of tune-up will help to see what, if anything, is going on.
Maybe change the oil again too. Now that its been to operating temp a few times it could flush some things out.
 

mattressking

10 digits to freedom
Joined
Nov 27, 2016
Messages
2,330
Location
San Diego, Calif.
Have you verified ignition timing and base timing is correct? Backfiring is almost always timing/ignition related. If that is correct and distributor is sitting about in the middle of its adjustment range (7* BTDC) then next is vacuum. If you're hovering at anything less than 15 you've gotta sort that out. Usually a big leak is fixed by advancing the timing...but it still runs pretty rough at idle and smooths out as rpms increase. Is the truck smogged as is or desmogged currently?
 

4Cruisers

Supporting Vendor
SILVER Star
Joined
Apr 2, 2015
Messages
6,443
The FJ60 is stock with all emissions in place, I’m the original owner. I’ll play around with the timing this morning and clean/replace the spark plugs.
 

mattressking

10 digits to freedom
Joined
Nov 27, 2016
Messages
2,330
Location
San Diego, Calif.
The FJ60 is stock with all emissions in place, I’m the original owner. I’ll play around with the timing this morning and clean/replace the spark plugs.

A fun check I like to do is verify the egr isn’t sticking, running a longer hose off the egr and sucking on it while the truck is running will unstick it or yield a change if the egr is sticking open and causing a large leak. Sometimes you can even hear it whistle. Another option is verify the ICS is working also - which would usually point to the emissions computer.

I’ve run into both scenarios causing very rough idle or not able to idle at all intermittently then moving to constantly.
 
Joined
Jul 6, 2020
Messages
174
Location
Poulsbo, WA
Check for corrosion under the distributor cap. Make sure the contacts on the cap and rotor are nice and clean.

How long has it been since it was running correctly?
HaHa. I actually laughed out loud. Telling @4Cruisers to check for corrosion inside his dizzy is like suggesting to @65swb45 that he might want to consider a carb rebuild. :rofl: Hey John how about you take one of those gorgeous rebuilds you produce in your laboratory and put it in your own truck!
 

cruisermatt

Un-manufacturable
Supporting Vendor
SILVER Star
Joined
Jul 22, 2012
Messages
9,681
Location
Orlando Florida
HaHa. I actually laughed out loud. Telling @4Cruisers to check for corrosion inside his dizzy is like suggesting to @65swb45 that he might want to consider a carb rebuild. :rofl: Hey John how about you take one of those gorgeous rebuilds you produce in your laboratory and put it in your own truck!

... ok but he hadn't checked it before I suggested it
And the last thing I would do in a situation like this is start swapping parts that could potentially change ignition timing... it was running fine when he parked it, why would anything in the ignition system be bad out of nowhere?
 

Users who are viewing this thread

Top Bottom