I did a search under “bucking” or “engine misfire” and I still haven’t found a solution. I have a 1987 pickup with a carburated 22r, 4-speed, California emmisions. About 40K on a rebuilt motor, with a new factory EGR and cat that have less than 20K miles on them. Igniter changed about 60K ago.
The truck has always run great, but I was driving on Saturday and suddenly developed a severe miss- almost a “buck”- plus lack of power/acceleration and inablity to use sudden throttle. I could feel it happen instantly. At higher throttle settings, it just growls and loses power. It also pings slightly, even on gentle acceleration.
It still starts easily, but the idle is now a little lumpy and inconsistent, and under load runs like lousy throughout the rev range.
No coolant loss, no coolant in the oil, no overheating.
I’ve gone for the easy and obvious: replaced the fuel filter, cap , rotor, plugs, plug wires, and checked the mechanical fuel pump to make sure it’s working. It checks out. I also tried running it with the gas cap off to see if the vent on the cap was blocked. No change. The old spark plugs, while worn, were a nice coco brown color.
I also took a look at the vacuum hoses and all are still supple- nothing with any cracks I can see. I don’t have a vacuum pump, but I did the “suck it and see” method with the vacuum advance, and can feel resistance and hear the ignition plate in the distributor move, with the other port nothing- no resistance, it’s just like sucking on a straw in the open air.
I don’t particularly want to get into the massive parts swap to figure it out, (money is an issue and I’ve bought all the tune up parts so far) but wanted to see if anyone else had experience with this? Not sure if it is coil/distributor related, (specifically vacuum advance), carb related, or emission control related (i.e. a plugged charcoal canister, or EGR vacuum modulator?)
Thanks in advance for the feedback.
The trouble sounds like it may be due to a timing issue.
It is not a plugged charcoal canister or an EGR related problem. The symptoms simply don’t fit.
It presnts itself as a typical vacuum leak. One way to check this is with a can of starter fluid. With the engine running, spray the starter fluid around all the potential vacuum leak areas. If the engine speeds up, you have a leak.
Another possibility is a bad accelerator pump or pump linkage. These cars have a lever and cam on the right side that actuates the pump. Over time this linkage can get corroded, gumped up, and stuck. If it doesn’t operate freely, it’ll cause your symptoms.
Or the problem could be internal to the carb. If the float and/or the needle valve that it operates is not operating properly it can causes insufficient supply to the venturi and starve the engine. The float operates the needle valve to keep the bowl full yet not pressurized. If the float is sticking up, or the needle valve is not opening properly, that can leave the bowl with insuffficient gas supply.
Timing issue is my first guess
This engine has a timing chain right??? If so it sounds like it slipped a tooth.
You are correct- the chain stretched, the tensioner hiccuped, and it did skip a tooth- which is a bummer because there is only 25K on it. I need to save up and do a double row timing chain conversion on it, but I just reset the timing for now.
Why a double row? I had a single row on my 22R that lasted 250K miles. The headgasket let go first, and the chain stretch was just under the limit. I went ahead and replace the chain, tensioner and guides while I had it all apart for the headgasket.
The best upgrade would be steel guides from LC Engineering. http://www.toyotacatalog.net/M1WebGear/ProductDetails.aspx?PartUniqueID=D7A1B610-0954-46E3-9231-27855E433DC2
Only because it concerned me that this chain stretched that much after 25K miles, and other things I’ve read is that the single row chain was a design flaw. But I’ll obviously do more research. Thanks!
Check the AAP diaphragm on your carburetor. These tend to rupture. I replaced mine on my 79 Celica (take off cover with three screws, remove spring and diaphragm and replace).
Symptoms of failed AAP include fuel in vacuum line leading to it.
Thanks- the problem ended up being the timing skipping and advancing a tooth.