ElMartillo

As stated in title, when cold (first start in am) cranks and barely fires. Will start if I floor the accelerator pedal, and runs rough until engine starts to warm. Once warmed up runs great, restarts great. I swapped temp sensor (from t-stat housing) with a spare with no change. Recent new fuel pump.

What to check?

Thanks!

Steve Hayes

When was the last tune up, plugs, cap, rotor, plug wires? When was the last time you replaced the air and fuel filters?

tjwalker

Any check engine light?

Agree that if not done recently, may be time for a full tuneup. Fresh secondary ignition parts like plugs, wires, cap, rotor go a long ways towards crisp starts. And as Steve mentioned, don't forget the fuel filter, which for a 1991, is a very easy inexpensive job....right along the fuel rail on the drivers side.

If no joy with that, even though you have a new fuel pump, I would get a fuel pressure gauge on it for some testing on those troublesome cold starts. Watch that gauge closely from the time the key is turned to the ON position until the engine fires for clues. For a 91, you need approximately 31 psi for the engine to fire.

bluejeep2001

Even though you changed out the t-stat sensor....disconnect it then try...if it thinks the coolant is warm it cuts back fuel...disconnecting it richens it up

bluejeep2001

Also...forgot to add this...pull off the vacuum line from the regulator...make sure its not full of fuel...if so...bad regulator

ElMartillo

Recent fuel regulator. Just put in a new air filter.

Finally got a day off to test. Fuel pressure after initial pump prime but before starting is 45 psi. Goes to 50 psi while cranking. Solid 45 psi while running.

OCCasionally it started this week cold but ran/idled rough until it warmed up. Today the ambient temp is a bit warmer, but was difficult to start, and ran poorly during idle though it took less time to smooth out.

Next opportunity I’ll get new plugs/cap/rotor/wires and see if that helps.

Thanks for the suggestions!