Random Backfiring - Toyota 22R

84Toyota4x4 · May 13, 2008

So, today my truck (which has a 22R and a Weber 32/36) started backfiring. I guess technically its forward firing, since its popping in the carb it sounds like. The fun part though, is that it comes and goes randomly under different circumstances. The only consistency is that I will be applying throttle every time. Different speeds, different RPMs, different amount of load, etc. I cant actually purposely replicate it. I drove around for probably 2 hours today, and it only did it about 4 or 5 times. It will just suddenly do it while applying throttle. I will let off the throttle of course, and slowly reapply throttle. If it does it again, I let off again. I do this until it stops. After its little "episode", it wont do it again for who knows how long.

Its not like earth shattering explosions, just decent force popping , almost like the timing is off or something. Thinking this, I hooked a timing light up to it, and the timing looks good. Looks good with the vacuum disconnected from the distributor, and advanced like it should be with it hooked up. Thats about all the diagnosis I did since I got distracted with something else on the truck. Oh, I also double checked and reset the fuel pressure to 3.5 PSI, and reset the lean best idle.

So, when I have time again, what are some things I should be looking at? Possible coil dying? Bad cap and rotor? Bad wires? Could this be a fuel pressure problem? I had a problem in the past with my fuel pump where it randomly just stopped working once while wheeling. No amount of tapping on it or anything would get it to work again. It just randomly started working again and Ive never had a problem with it since - unless this is one.

~T.J.

84Toyota4x4 · May 13, 2008

No one?

~T.J.

GaryTJ · May 13, 2008

could be weak spark or lean fuel conditions.

With your carb, I would start there. They are notorious for dirt in the air bleeds.

take a can of carb clean and clean it up real good inside, especially where there is any kind of jet/bleeds and try that first.

dkbstoy · May 18, 2008

its probably cross firing check the distributor cap for excessive build up on the electrodes or just lots of dust/mud. if nothing there try running your hands down the plug wires while its running if you get fried you need some new wires. but id bet on dirt in the cap its happened to me a couple times... if it were fuel related throttle position would probably affect it.

ljtoy · May 18, 2008

dkbstoy said:
its probably cross firing check the distributor cap for excessive build up on the electrodes or just lots of dust/mud. if nothing there try running your hands down the plug wires while its running if you get fried you need some new wires. but id bet on dirt in the cap its happened to me a couple times... if it were fuel related throttle position would probably affect it.

backfire(?) through the carb can be caused by:

(1) intake valve just opening or possibly sticking while the next cylinder in the firing order is progressing through the cycle known as valve over-lap.
{ie - check valve clearance - hot - possible weak valve springs}

(2) static crossfire. this occurs when one or more plug wires lose the ability to contain the high voltage going them to ground at the spark plug. this is how the current normally jumps that plug gap. shortest path to ground...

(3) step up and install a FACTORY OEM CAP AND ROTOR. I can put a TOY on the scope and show you the difference between aftermarket and factory.

(4) Ditto on weber carbs being flaky.. All kinds of strange stuff can happen. I had a 75 Chev backfire through the intake. Carb was Holley 4bbl and it blew off one of the primary butterflies. Talk about a "fast idle" !!

84Toyota4x4 · May 18, 2008

Sounds good. I will take a look at that stuff. I put some "cheapie" plug wires on it after the OEM ones I had on it melted on the header when they fell out of the holders. Those cheapies may have kicked the bucket. Ill pull the cap and rotor and replace as necessary as well. Its a rebuilt motor within the last few years (by me), so I would really hope that its not a mechanical problem with how meticulous I was during assembly and such.

I also need to monitor my fuel pump. I had a problem with it cutting out on me randomly a couple times. But, when its doing this stumbling/backfiring problem, the pressure is steady through it all from what I have seen so far. Im hoping its ignition related. I plan to test the coil as well just in case. Thanks for the advice. I need to have exhaust built for this thing again now too though. I cant really run it around too much without it, haha.

~T.J.