1981 Fj40 backfire through exhaust when hot

[F16Roo]

OK, had my 40 since 1988 always runs great. Recently when it gets hot it intermittently starts misfiring with occasional severe backfire in exhaust. Replaced plugs, dizzy cap, and rotor. Still going on. Coil checks at .8 ohm cold ( factory resistance specs .5 to .7.) Where should I go next? Thanks in advance.

 

[yotamaster]

OK, had my 40 since 1988 always runs great. Recently when it gets hot it intermittently starts misfiring with occasional severe backfire in exhaust. Replaced plugs, dizzy cap, and rotor. Still going on. Coil checks at .8 ohm cold ( factory resistance specs .5 to .7.) Where should I go next? Thanks in advance.

I would start looking into the carburetor. Could be running to Rich.

 

[F16Roo]

Yea maybe...still running stock with all the emissions "spaghetti" attached. Not really sure where to start on that. Just wondering why it would run fine cold, but misfire only after getting hot?

 

[F16Roo]

Also, meant to ask if it possible the coil causes misfire due to increased resistance when hot?

 

[yotamaster]

Here is a list a fellow member created of local shops in you area.
Hope this helps.

 

[SteveH]

Swap in a spare ignitor, if you have one. Perhaps an FJ60 ignitor would fit that year FJ40, and those are likely more common.

 

[F16Roo]

Thanks for the info on repair shops...was planning on taking it up to Trollhole Cruisers for de-smog and to restore engine....just haven't gotten it up there yet. Outside my 40 is very nice...all original, virtually no rust, etc....engine not so much. On the igniter...I don't have a spare, but I have factory service manual that has the procedure to test the igniter...I'll give that a try. Is it possible igniter could only malfunction when hot? I fired it up yesterday...cranked right up and ran fine. But I know after 15 minutes or so of driving misfire starts again. Perplexes me. BTW, I have a complete set of FSMs for 1981 Land Cruisers...engine, electrical, body, emissions, etc. if anyone needs any specific information from one.

 

[Cromagnon]

It is absolutely possible that the ignitor starts to act up once it is warm. I had an issue where the engine would loose power, start backfiring and finally stall while going down the highway. All of the symptoms pointed to fuel starvation and I replaced a lot of parts trying to eliminate the problem. Ended up being the coil. What a learning experience.

 

[F16Roo]

Took 40 out today and it ran fine...guess I don't understand intermittent nature of misfire. When I say backfire...I mean bad...blew baseball size hole in muffler. Seems to only happen when really hot. Any more ideas?? I've driven it to TX, AZ, CO, TX and back to SC...never missed a beat..Anyway, attached a pic of the 2F...like I said could use some "cleaning up."

 

[Cromagnon]

If the malfunction is related to only a certain condition(s) you will have to replicate that/those condition(s) to troubleshoot it. You can replace parts one at a time until the trouble goes away but that can get really annoying and costly. You will think the problem is solved and then it will rear its ugly head at the worse possible moment. If you do the swapnology method go from the easiest/ cheapest to the hardest/ most costly, unless the symptoms point to an obvious culprit. Let us know what you find please.

 

[RustyNailJustin]

Have you tried replacing or capping the ABV? (Anti Backfire Valve)

 

[fjc-man]

How many ( if your odometer has always worked) miles on your 40?

 

[1911]

Backfire through the exhaust is usually the result of either the carb mixture too rich, retarded timing, or air leaks in the exhaust manifold or headers. If your carb was the culprit, it would do it all the time, not just intermittently. So, I would look for leaks in the exhaust and also check the vacuum advance on your distributor (if you have one - you didn't say what year 40 but it looks like a late one). Vacuum advances rust out pretty commonly.

 

[F16Roo]

Odometer reads 149600...but it works when it wants to. It is a 1981 model. I'll keep at it until I figure this thing. Although from some research looks like a bad coil can also cause backfire...i.e., no or poor ignition. May change it out just to see. Just doesn't seem to be running rich....no evidence on exhaust and plugs looked good when I changed them. Don't know about leaks yet. Not sure I know about ABV...I'll check in the emissions manual. Thanks.

 

[RustyNailJustin]

This is the ABV air bypasses valve or anti backfire valve.
Easy to see if it's the culprit. Pull the large hose and cap it and go for a test drive.

 

[F16Roo]

Now I just got to find it in the tangle of vacuum lines!

 

[F16Roo]

Thanks for all the inputs...think I've finally got this fixed. Thanks to FJC-man who suggested I take a look a electrical portion of the ignition switch. Changed it out in 15 minutes and haven't seen the problem since then. Now just got to replace blown-up muffler.