Seafoam top engine cleaner (temporarily) solved misfiring? (1 Viewer)

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FZJ80inTX

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Oct 3, 2018
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Among the numerous idling issues I'm having with my '94 FZJ80 (OBD1) is a misfire. I tested the wires and replaced the plugs and that didn't change anything. So my buddy suggested I try a bottle of seafoam top engine cleaner.
Within a few seconds of spraying it in the misfire completely went away and the engine ran smoother than it's ever ran (since I've owned it). After the treatment I drove it around as directed and the engine felt like brand new.

I started it back up this morning and the misfire is back & the engine is back to being shaky.

Any ideas how/why the seafoam temporarily fixed the misfire? Could I potentially have a failing injector?
 
I'm having a similar problem with my '94. I left my office for an appointment and it started to run really rough and weak, felt like I dropped one or two cylinders, idles rough and the CEL light came on. Made it to my appointment and after two hours I started it up and it seemed to run a bit better, no CEL. Filled my tank, added a bottle of SeaFoam and made it home. Next morning the truck was running great. Ran some errands and now its stumbling again but no CEL... Going to replace both fuel filters (truck has 235K and I have no history of filter replacements so figured its a good place to start) Cap & Rotor and plugs. Wires "look" good but will likely replace next if problem persists.

Does this strategy make sense? Not sure why the CEL came on once and not again?
 
FZJ80inTX said:
Among the numerous idling issues I'm having with my '94 FZJ80 (OBD1) is a misfire. I tested the wires and replaced the plugs and that didn't change anything. So my buddy suggested I try a bottle of seafoam top engine cleaner.
Within a few seconds of spraying it in the misfire completely went away and the engine ran smoother than it's ever ran (since I've owned it). After the treatment I drove it around as directed and the engine felt like brand new.

I started it back up this morning and the misfire is back & the engine is back to being shaky.

Any ideas how/why the seafoam temporarily fixed the misfire? Could I potentially have a failing injector?
Click to expand...

This might be a stretch, but have you checked the state of your rubber intake tube between the air cleaner & the manifold? If its cracked & pulling in too much air, the seafoam may have temporarily enriched the air / fuel mixture enough to allow it to run smooth, but once the seafoam burned off the mixture is out of whack again. I used a roll of cheap electric tape on mine until the replacement part arrived.
 
FloydtheDog said:
This might be a stretch, but have you checked the state of your rubber intake tube between the air cleaner & the manifold? If its cracked & pulling in too much air, the seafoam may have temporarily enriched the air / fuel mixture enough to allow it to run smooth, but once the seafoam burned off the mixture is out of whack again. I used a roll of cheap electric tape on mine until the replacement part arrived.
Click to expand...

The previous owner replaced the intake tube the week before I bought it (Sep. 2018).
The problems I'm having didn't start for about two months after I took ownership of it (Nov. 2018).

I did find a very cracked, possibly disconnected vacuum line under the intake manifold on the driver's side. It's the short (maybe 5-6" long) line that comes off the T fitting that is downstream from the charcoal canister.

I also replaced the charcoal canister and the thicker vacuum lines that come off of it, which is how I discovered the damaged/lose vacuum line.
 
I'm still having idling issues and misfires. I tried another canister of sea foam and it again temporarily fixed The misfiring.
I also replaced some vacuum lines and the charcoal canister this weekend and it seemed to rectify things, but it all came back.

I've got a multi meter on its way so I'll be checking the IAC and any other component I can easily reach.

If that doesn't yield any results I'll be removing the throttle body and intake over Christmas break to clean everything thoroughly and replace every vacuum line, check valve, and any other thing I can think of.
 
Sounds to me like you have a vacuum leak. The sea foam is adding fuel which is then bringing the A/F mixture back towards 14:1. I would be replacing all your vacuum lines. I would also be checking the vacuum and see how it compares to the FSM
 
Anyone know what this connection circled in red in the picture is for?
The previous owner removed the EGR & PAIR systems so I imagine it has to do with one of them.

For grins I pulled that bridged wire out and drove it around a bit. The idling issue still remains, but it does seem like my misfire issue is gone or at least reduced now.

The truck still hasn't thrown a CEL yet, and I do check that the light illuminates before start up.

B011728E-D4E7-4136-9098-6FE168B7C017.jpeg
 
That's tube connector for the egr temp sensor
 
Tedward said:
OBDI need only be jumped/bridged. Your good.

OBDII needs resistor.
Click to expand...
Is there any reason why bridging it would negatively effect anything?
Since removing the wire bridge I feel like most, if not all, of my misfiring has gone away. It STILL won't idle properly, but the engine seems to be much smoother.
 
I disconnected the temp sensor wire from the temp sensor on my 94 four years ago and used no jumper between the terminals with no negative results or CEL. Some time later I bought a brand new wire harness that came with a blanking plug in that connector that bridged the terminals. Experimentation will tell you what works on your rig.
 
Another item you might check is the engine wiring harness that passes right next to the HOT EGR pipe. That pipe has been known to burn holes in the engine wiring harness shorting one of the injectors, thereby causing that fuel injector to stop spraying fuel. Adding sea foam could be covering up for the lack of an injector pulse to one cylinder, providing fuel to that cylinder so you don't have a misfire for a few seconds.
 
FZJ80inTX said:
Yeah I've replaced all of the easy to reach lines already this week.
This weekend I'll replace everything under the intake manifold when I remove it.
Click to expand...

Quick way to test that theory is get a cheap vacuum brake bleeder/tester from China freight. If vacuum is good then try disconnect the battery for 10 minutes to reset the ECU and have it relearn, I had to do that once also.
 
What is good vacum exactly and where from? Seriously.
 
Tedward said:
What is good vacum exactly and where from? Seriously.
Click to expand...

Vacuum is good meaning the system can hold a vacuum or negative pressure which can easily be tested with a cheap vacuum test thingofmajiggy!
 
Last edited:
Qball said:
...If vacuum is good then try disconnect the battery for 10 minutes to reset the ECU and have it relearn, I had to do that once also.
Click to expand...

If memory serves, I think the same effect can be achieved by removing your EFI fuse for like a minute or so and you won't loose your radio / clock settings. Not 100% sure this works on ODB1 models, but I used to use this method to reset the CEL on my '95 (ODBII).
 
When you say hold vacum, I have a thingamagigy, you mean whilst running it after it what. U remember something in the FSM but didn't understand where or when or how much vacum. Have problems like the OP so wondering for the both of us.
Any more experienced insight you can give?
 
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