I have a 91 4x4 v-6 5-speed which sputters BADLY after warmup. It only sputters while in gear and starting off. After 3500-4000 rpms, it gets up and goes - like a shot of NO2. This just started in the last few weeks, but seems to be getting worse. I have noticed that it is okay until after the truck warms up, then the miss/sputter starts. Even if you get out for 30 minutes all returns to normal for 5-8 milutes , then it returns. The truck has 255,000 miles, but has been taken care of. I am on my second tankfull of STP fuel injector cleaner.
Any ideas? Anyone? Thanks in advance for any help.
It's hard to say, but it sure sounds like it might be a fuel or induction problem. Based on the fact that the condition seems to be getting worse so quickly -- if I were forced to make one -- my SWAG would be that your fuel pump is going bad.
The first thing I would check, however, is to make sure there are no vacuum leaks, particularly in the air intake line.
Then, I would check the diagnosis system to see if any codes are output. I posted some information a while back on how to do this (look for the subject "Engine Light"). If there are codes, address the issue and see if that helps.
If there are no codes and you are pretty confident that all cylinders are getting fire, you need to move on to the fuel system.
You need to check the fuel pressure. It sounds like the fuel pump is running, so there is no need to check that. Basically, you need to hook a pressure gauge up to your LH fuel supply line (runs into the back of the air intake chamber.) I don't know an easy way to do this without a special rig because this is a high pressure line. I rigged a hook-up a few years back with a fitting that Toyota supplied. You check the pressure by turning the ignition on and shorting the top and bottom connectors in the first column of the diagnostic connection (Fp & B) - this makes the fuel pump run without starting the engine.
The pressure is supposed to be between 38-44 psi when performing this test. If it is not within this range, you have either a clogged fuel filter, a bad fuel pump, or a faulty pressure regulator. The regulator can be checked with the same rig but allowing the engine to run. With the vacuum line connected to the regulator and the engine idling, the pressure should drop to between 33-37 psi. If it doesn't, then your pressure regulator should be replaced. If the pressure never gets up to this range, you have either a bad fuel pump or the filter needs to be replaced.
If your fuel pressure is okay, that leaves the following:
- Fuel Injectors (Connections and Flow) - Spark Plugs (Condition and Gap) - Air Flow Meter - Water Temp Sensor - Air Temp Sensor - Air Temp Sensor - ECU
Several of these can be checked using a voltage meter.
Sorry there is no magic solution to your problem. However, the above should represent a fairly sound approach to diagnosing the issue.
I would have to agree with Luther. Sounds like a vaccum leak but when was the last time you changed your fuel filter? I would also check your injectors the procedure is not that difficult to complete you need about a
Actually, I PERSONALLY have not changed the fuel filter, but I've only had the truck for about 30,000 miles.
What is the procedure for checking the injectors? I thought they needed to be cleaned with special equipment - and its not normally done by do-it-yourselfers.
I would also check the EGR valve. I read somewhere on the internet that the EGR valve monitors the amount of fuel that the motor needs based on the current running temp of the motor. The warmer the motor the less amout of fuel is needed. You might have a bad EGR valve that will cause your motor to run rich when it warms up thus causing it to sputter. Then when it cools down for 30 minutes it runs great until it warms back up again.
Well, Im almost thru my second tankfull of gas and STP injector cleaner (the good expensive stuff) and the problem SEEMS to be getting better.
I will continue to look at the other options that everyone has mentioned.
Thanks
-ysgi
the EGR valve monitors the amount of fuel that the motor needs based on the current running temp of the motor. The warmer the motor the less amout of fuel is needed. You might have a bad EGR valve that will cause your motor to run rich when it warms up thus causing it to sputter. Then when it cools down for 30 minutes it runs great until it warms back up again.
Checking the injectors can be done at home. I have the factory manuals, although it not in front of me at the moment, but all you need to do is remove the injectors and then hook up the positive and negative lead from the battery and dip the feed side of injector in fuel. If it sprays clean it is good. In a nut shell that is what the manual says. Also on the fuel filter, it is recommended to change them at least every 30,000 miles or so.
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