Hi,
A slight constant backfire occures on deceleration. Engine seems to run fine at any tempurature with out a load but when accelerating coughs and sputters until it finally smooths out at 4000 (?). At 40 mph or so I feel a slight loping vibration that feels like a wheel out of ballance but it changes "off-throtle". Poor fuel economy.
New exhaust, cap and rotor, spark plug wires, fuel filter, replaced the #3 plug as it was loose in the head, the others were cleaned and re-gapped. Drygas and premium fuel. New fuel pump. The symptoms change somewhat but the trouble is the same.
Throwing some ideas around with my mechanic: Bad excellerator pump?, Vacuum leak? Trouble with vacuum advance at the distributor? He'll have the truck this week to replace a wheel axle seal and new brake shoes.
Ideas?

Is it the 22r or 22re? Carb or Fuel Injected?
Sounds very much like a vacuum leak or a timing issue. Also how many miles are on it? These engines need to have the timing tensioners and idlers changed around 180K or so. Especially if you donÆt run a OEM oil filter with the check valve in it causes premature ware on the tensioners.

On one 22re I had the tensioner fail and the chain wore a hole through the side of the housing. It ran pretty crappy for a while befoe the guy boght it over for me to look at.

Something maybe to have him check.

22r Carburated, 327,000 miles. The truck has a two year old front engine cover and gear set as the timing chain did eat a hole into the water pump housing. At that time the head was rebuilt and a shim was installed to raise the deck height and help prevent the problem. There are none of the symptoms of a tensioner failure like slapping chain noise in the front of the engine, or oil in the anti-freeze.
I can check the compression of the cylinders and look at the valve adjustment to try to find out if they're totally wacked out, but I can't imagine either would be enough to make it run this badly.
On my way home tonight, I was coasting downhill in third gear with the throttle off and the backfiring was constant, and that I think is the "crux of the buisquit."

What I found on About.com "auto repair"

Toyota Pickup Backfires Bad

Q. Dear Vince, I have a 1977 Toyota Hi Lux Pickup with the 20R Engine, 128,000 miles, four speed stick with a fifth gear for overdrive. The engine has backfired for years and has got worse over time. The backfire is severe enough that it blew open the muffler.


I have rebuilt the carburetor, set the timing and tuned the engine. No one seems to have the answer. Am I stuck with a backfire forever or is there something I missed? Your help is very much appreciated.

Best wishes,
Bill


A. There are a couple of things that can cause the backfiring. First is a tight valve. If you have an exhaust valve that is too tight and not closing completely, it will backfire through the exhaust. So I would check the valve adjustment first. It's still a good thing to do even if it doesn't solve the problem.

Another possibility is the Deceleration Fuel Cut System. This system is used to prevent overheating and/or after burning in the exhaust system when the vehicle is decelerating by momentarily cutting off the fuel supply in the system.

Here is the troubleshooting procedure:

Check vacuum hose and wiring for damage or improper routing and repair or replace as necessary.
If engine starts, proceed to step 5.
If engine does not start, disconnect wiring harness connector to fuel cut solenoid and apply battery voltage to solenoid. If engine now starts, replace computer.
If engine still does not start, check related systems.
If engine starts in step 2 or 4, pinch hose between vacuum switch and carburetor with engine idling.
Gradually increase engine speed to 2500 RPM. If engine misfires slightly between 2,000 and 2,500 RPM, reduce engine speed and release pinched hose. Test is complete.
If engine does not misfire, disconnect wiring connector from vacuum switch.
Gradually raise engine speed to 2,500 RPM. If engine misfires between 2,000 and 2,500 RPM, replace vacuum switch.
If engine does not misfire, disconnect connector from solenoid valve. If engine idles rough, replace computer. If not, replace solenoid valve.