FJ60 OVERHEAT / BACKFIRE / CAT MELT (1 Viewer)

[SnapKeegan]

Hey gang, not new to Mud but I'm a first-timer with posting. I've been trying to diagnose a problem for a while now and my searches on this (and countless other) site's threads and I feel no closer.

I have an '85 60 that's been giving me trouble for a while. The PO had desmogged and installed a Weber 38, and from time of purchase (I drove it back from OR to OH) it had trouble with overheating and dieseling after shut off. There has always been spits of oil from the tail pipe, but no white smoke.

Once home I had my mechanic try to solve it, we replaced the belts, T-stat, flushed the heater core (one original symptom was no hot air blowing in the cabin), and burped the engine.

It was fine for a while, then one day lost power, choked out, then died. Mechanic said the cat had melted down from excess heat/being clogged, and he bored it out (as it was largely useless now).

Was "fine" again for a while, but continued its dieseling problem and was struggling to idle once warm. Had a friend try to help me diagnose and the carb was definitely in need of tuning, which we did in an afternoon. Ran it around town for a while with no issue, then took it on the highway for the real test, which after 30 minutes it choked out, then literally blew up my muffler from a significant backfire. Limped it to an exhaust shop to replace components but now the overheat issue is back in full swing..... kind of at a loss here.

I know most of this is largely a carb issue (yes I'm aware of the preference for OEM carbs...I have one I am planning to put on some day), but the spitting from the tail pipe is concerning (compression test is the next plan), and I (possibly ignorantly) am assuming the overheat issue and carb status are separate issues...

Any help would be greatly appreciated.

 

[mountainibis]

Have you checked for vacuum leaks when it’s hot? It could be a leak that doesn’t show up until everything warms up and expands. Possibly the manifold or carb isolator? A vacuum leak would cause the motor to run lean and motors that run lean run hotter than they should.

 

[SnapKeegan]

Have you checked for vacuum leaks when it’s hot? It could be a leak that doesn’t show up until everything warms up and expands. Possibly the manifold or carb isolator? A vacuum leak would cause the motor to run lean and motors that run lean run hotter than they should.

We removed the carb and reseated everything with RTV. I also replaced the exhaust manifold gasket (once when the cat melted and again when I replaced the muffler) as it blew out too (which I thought was from the clog and backup of gases). We also installed a fuel regulator after the fuel pump to keep pressure consistent and helped the dieseling but obviously the backfire still indicates a fuel problem.

 

[Seth S]

Go back to the original carb sooner. When they did the desmog did they have the distributor advance recurved?

 

[Seth S]

Your cat is useless with the desmog. If you don’t have the air pump system on there then the cat is never going to work proper again. It’s just going to load up and run hot like you found.

 

[SnapKeegan]

Do you have the original carb still? When they did the desmog did they have the distributor advance recurved?

I don't have the original, but I do have one that I purchased off another rig. I'm not sure about the distributor recurving (although I've read that's a key step from the how-to's I've read). Is there a way to tell if the dizzy is recurved by looking at it?

 

[SnapKeegan]

Your cat is useless with the desmog. If you don’t have the air pump system on there then the cat is never going to work proper again. It’s just going to load up and run hot like you found.

I figured as much (especially after it melted), but just like with a lot of things on here I've seen keep it and I've seen lose it. Guess it makes no difference now to just put on a straight pipe

 

[Seth S]

I figured as much (especially after it melted), but just like with a lot of things on here I've seen keep it and I've seen lose it. Guess it makes no difference now to just put on a straight pipe

Any CAT needs a fuel mixture that oscillates between rich and lean. When the desmog is done the mixture has very little fluctuation and this is what causes the cat to stop working....often it gets loaded up or overheats. This is the down side to doing a desmog and why its so important to review your states smog equipment rules.

 

[Seth S]

I don't have the original, but I do have one that I purchased off another rig. I'm not sure about the distributor recurving (although I've read that's a key step from the how-to's I've read). Is there a way to tell if the dizzy is recurved by looking at it?

Not really an easy way to look at the distributor and tell if it was recurved. I am guessing yours wasn't because most people dont know about this step. The reason for the recurve is that the EGR system slows down the ignition burn. Remove the EGR and you need to compensate.....a common side effect is to have pinging with low octane fuel...excessive pinging can result in more engine heat and can lead to a melted or holed piston.

 

[SnapKeegan]

Any CAT needs a fuel mixture that oscillates between rich and lean. When the desmog is done the mixture has very little fluctuation and this is what causes the cat to stop working....often it gets loaded up or overheats. This is the down side to doing a desmog and why its so important to review your states smog equipment rules.

Thankfully I live in the free state of KY so no smog rules for me to worry about.

 

[Seth S]

Thankfully I live in the free state of KY so no smog rules for me to worry about.

Depending on what your budget is you should consider doing a Sniper conversion. You could sell the weber carb and the other original carb you got and pay for a good chunk of the sniper parts. In the end you would have a fuel injected truck that would work with a CAT if you decided to run one.

 

[SnapKeegan]

Depending on what your budget is you should consider doing a Sniper conversion. You could sell the weber carb and the other original carb you got and pay for a good chunk of the sniper parts. In the end you would have a fuel injected truck that would work with a CAT if you decided to run one.

I'm good on that, at least for now. I really just want these big issues to get solved. I plan on replacing the rad and water pump next...will split the shroud while I'm at it....not sure if the fan clutch is necessary as well as it's working fine right now

 

[2mbb]

I'm good on that, at least for now. I really just want these big issues to get solved. I plan on replacing the rad and water pump next...will split the shroud while I'm at it....not sure if the fan clutch is necessary as well as it's working fine right now

I'm not sure what your answer means-are you trending towards an EFI system or do you want to try to keep the carburetor set up?

If the latter, I agree you should get rid of the weber and go back to an aisan two barrel. You have a used one, so that should probably be rebuilt--either do it yourself or send it to one of the trusted rebuilders recommended via this forum. I think it is unlikely you will find a local shop that will do this work the way it needs to be done. You can also purchase a non-US version (perfect for a desmogged engine) via City Racer LLC or gamble with a knock off from ebay.

find the desmog thread and go through it to make sure the PO did everything and that what he did was done correctly. You can get help here on MUD but you will have to provide more details and pictures I think.

 

[SnapKeegan]

Any CAT needs a fuel mixture that oscillates between rich and lean. When the desmog is done the mixture has very little fluctuation and this is what causes the cat to stop working....often it gets loaded up or overheats. This is the down side to doing a desmog and why its so important to review your states smog equipment rules.

What's the consensus on straight pipe and

I'm not sure what your answer means-are you trending towards an EFI system or do you want to try to keep the carburetor set up?

If the latter, I agree you should get rid of the weber and go back to an aisan two barrel. You have a used one, so that should probably be rebuilt--either do it yourself or send it to one of the trusted rebuilders recommended via this forum. I think it is unlikely you will find a local shop that will do this work the way it needs to be done. You can also purchase a non-US version (perfect for a desmogged engine) via City Racer LLC or gamble with a knock off from ebay.

find the desmog thread and go through it to make sure the PO did everything and that what he did was done correctly. You can get help here on MUD but you will have to provide more details and pictures I think.

Roger that. What I meant to say was I plan on keeping a carb set up. Pics of the engine bay forthcoming. The PO did include a bunch of manuals with the sale, inclusive of the desmog procedure (which matches those found on here) I assume he followed the correct procedure but only one way to find out...

 

[Seth S]

What's the consensus on straight pipe and

Roger that. What I meant to say was I plan on keeping a carb set up. Pics of the engine bay forthcoming. The PO did include a bunch of manuals with the sale, inclusive of the desmog procedure (which matches those found on here) I assume he followed the correct procedure but only one way to find out...

If your exhaust is good I would just remove the cat and put in a straight pipe in its place.