Cold Blooded problems
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Freshman User
Joined: Feb 2004
Posts: 47
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Cold Blooded problems
Got a 1990 F250 with the 351w in it. When its cold and you apply the gas, it stumbles then picks back up, sometimes though it'll shut off! When its warmed up it acts fine, wont stall out or stumble or anything. Its had a basic tune up, to my knowledge thats cap/rotor oil possibly wires and spark plugs havent really looked at those to closely.
Senior User
Joined: Feb 2004
Posts: 155
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From: Alaska
Have you checked for codes? If your check engine light isn't on and assuming it works there may still be a code in the continues memory. Try looking for a code first. That is where I would start. Let us know if you find anything.
Elder User
Joined: Sep 2004
Posts: 941
Likes: 4
It sounds like the computer is failing to enrich the mixture sufficiently for cold operation. This could be because the computer does not recognize that it is cold. Check the ECT and ACT sensors.
Another possibility is that the engine is running too lean for some reason. Once the engine is warmed up, the computer uses the oxygen sensor feedback and adjusts the mixture ratio sufficiently to correct for whatever is causing it to be too lean. Low fuel pressure is the most likely cause of something like this. A vacuum leak is a possibility, though it takes a pretty bad vacuum leak to create problems with a speed-density setup.
If the problem only happens at off-idle tip-in, your TPS may be bad or adjusted incorrectly.
Does the fast-idle function work correctly at cold temps? The computer should be boosting idle speed to 2000 RPM or so for about one minute after startup on a dead cold engine. If it does not, the IAC may be dirty, or we may be back to the "it doesn't know that it is cold" issue.
Another possibility is that the engine is running too lean for some reason. Once the engine is warmed up, the computer uses the oxygen sensor feedback and adjusts the mixture ratio sufficiently to correct for whatever is causing it to be too lean. Low fuel pressure is the most likely cause of something like this. A vacuum leak is a possibility, though it takes a pretty bad vacuum leak to create problems with a speed-density setup.
If the problem only happens at off-idle tip-in, your TPS may be bad or adjusted incorrectly.
Does the fast-idle function work correctly at cold temps? The computer should be boosting idle speed to 2000 RPM or so for about one minute after startup on a dead cold engine. If it does not, the IAC may be dirty, or we may be back to the "it doesn't know that it is cold" issue.
