3000GTVR4

I have a 1991 SR5 pickup, 3.0 5speed, 4wd with 198k on it.

A few months ago I had a really bad misfire issue. It turned out that the ceramic insulator had broken off the tip of a sparkplug. So I changed all plugs to NGK coppers, factory wireset, and new cap and rotor. Since the change everything seems to be smooth except for one issue

If I left of the gas really slow, like on the highway slowing down slowly to maintain a set speed, I get a really bad misfire. It happens for a split second, check engine light flashes quick, then its like nothing happened.

First I thought the coil wire might be loose, but i check and everything feels snug. Then realized I can make it do it at a very set driving condition so I dont think its a loose connection.

Any thoughts?

3000GTVR4

Anyone?

limon32

Considering the symptom is reproducible with a change in throttle, i'd initially suspect the TPS. Although you would think that would be reproducible with a slow increase in throttle as well, you might try that and see if it misfires.

A test of the TPS is free and instructions can be found all over this site. Swap a different one in if you can get one cheap, thats a good test too.

betelnut

I'm new to my Toyota and not too familiar yet, but if the check light comes on, would there be an engine code? Engine faults are supposed to be logged, and I think I read you don't need an ODM tool to read the Toyota codes, just a jumper in the diagnostic block.

abecedarian

That is correct. Some CEL codes are 'hard', meaning they trip the CEL and the light stays on, while others are 'soft' and light up the CEL when the problem occurs but will turn it off when the problem subsides. Also, most codes are retained by the ECU even when the ignition is turned off so they can be recovered even if the CEL is not on at the time the codes are retrieved.

Pulling stored codes only requires inserting a jumper between the Te1 and E1 terminals in the check connector then, with the a/c off and not depressing the clutch pedal or clutch-start cancel switch, turning the ignition switch to "on" without starting the vehicle, then counting the flashes the CEL makes. The diagnostic check connector is mounted under the hood, to the side of the fuse block near the battery, and there should be a diagram on the underside of the cover over the check connector showing which terminal is which.

3000GTVR4

I just tried pulling the codes this way, and the check engine light just keeps flashing. Keeps flashing fast for a solid minute.

limon32

Failed ECU?

2DoorRunner

quick flashing like that means there are no codes.

3000GTVR4

Hmm so that would mean that my ECU is not storing the code when I get the misfire.

When I get the mistfire its a very split second thing. Misfire, check engine light flashes off just as quick as it does on, then normal.

2DoorRunner

You are correct, its not storing your misfire code.
I dont think its a problem with the ecu, i think it is just reading the misfire as a temporary code or something. Not quite sure, im no expert.

limon32

That would mean whatever is causing the misfire is not caused by a sensor. I would check fuel pressure.