Paul-1991
11-03-2021, 06:43 PM
I've got a 1991 4cyl Mighty Max that takes 2 or 3 tries at half throttle to start it. The idle will then go back and forth between a very low rpm to a high rpm until it warms up. When driven cold, it has very poor acceleration and around half throttle gives the most acceleration.
First I changed the plugs, plug wires, and distributor cap. Those were all bad and it helped smooth the engine when warm. I then cleaned the MAF sensor. No change. I sprayed carb cleaner anywhere I thought a vacuum leak could occur but didn't find anything. I then changed the PCV valve and vacuum hose + breather vacuum hose. While changing the PCV valve, I sprayed a half a bottle of carb cleaner down the vacuum hose to clean the oxygen sensor (slowly enough to not burn the cat and changed the oil after immediately). I then cleaned the egr valve, but didn't check it for a vacuum leak yet. I just picked up some 5/32" vacuum hose which I think is the size I need to replace the small vacuum lines to the egr valve. Then I'll try disconnecting it and manually compressing the egr valve while plugging the end with my finger to check for vacuum...I think that should work. Cleaning the egr valve didn't help.
Other info to be aware of. I had to use a bottle of head gasket leak stop a couple years ago. A little after that I changed the radiator with a slightly larger one when the original cracked and developed a leak. The timing belt is old, but it isn't backfiring, so I don't think it has slipped. The thermostat is stuck open, and I haven't changed it yet, so it runs cool only reaching normal temperature if I let it idle a long time. I have some Redline Injector Cleaner in the fuel to clean the injectors. The ECU was changed once at about 100k miles a _long_ time ago. It's got 207k miles now. Air filter doesn't have many miles at all and is clean.
What am I missing? Could it be loosing fuel pressure with a very slow leak causing it to be hard to start? Some other potentially bad part?
Thanks
First I changed the plugs, plug wires, and distributor cap. Those were all bad and it helped smooth the engine when warm. I then cleaned the MAF sensor. No change. I sprayed carb cleaner anywhere I thought a vacuum leak could occur but didn't find anything. I then changed the PCV valve and vacuum hose + breather vacuum hose. While changing the PCV valve, I sprayed a half a bottle of carb cleaner down the vacuum hose to clean the oxygen sensor (slowly enough to not burn the cat and changed the oil after immediately). I then cleaned the egr valve, but didn't check it for a vacuum leak yet. I just picked up some 5/32" vacuum hose which I think is the size I need to replace the small vacuum lines to the egr valve. Then I'll try disconnecting it and manually compressing the egr valve while plugging the end with my finger to check for vacuum...I think that should work. Cleaning the egr valve didn't help.
Other info to be aware of. I had to use a bottle of head gasket leak stop a couple years ago. A little after that I changed the radiator with a slightly larger one when the original cracked and developed a leak. The timing belt is old, but it isn't backfiring, so I don't think it has slipped. The thermostat is stuck open, and I haven't changed it yet, so it runs cool only reaching normal temperature if I let it idle a long time. I have some Redline Injector Cleaner in the fuel to clean the injectors. The ECU was changed once at about 100k miles a _long_ time ago. It's got 207k miles now. Air filter doesn't have many miles at all and is clean.
What am I missing? Could it be loosing fuel pressure with a very slow leak causing it to be hard to start? Some other potentially bad part?
Thanks