Odd engines stumble...

[andrewm]

So I've got one I havent been able to figure out with basic trouble shooting, and not really sure what could cause it.

Rough idle on initial start about 30% of the time. Occasional power loss/stalling while driving. Economter will typically say I'm dumping fuel like crazy and getting 15mpg at interstate speeds while cruising.

Afterwards, vehicle will not start for a few minutes. Then it's perfectly fine until the next incident.

I'm starting to lean towards a ground, and I am gonna make an additional ground wire tonight when I get home - but no CEL, nothing blinking at me. When she runs normal, runs like a top. I have been unable to source a vac leak anywhere. Fuel filter has been replaced - which also doesnt add up to the poor mileage unless there is a leak, but I smell no fuel.

Anyone seen something like this before?

[Exodus_2pt0]

Tune up? I have been getting a Cylinder 6 misfire on cold starts lately, then once it warms up the car returns to normal. I've had copper plugs in there for a year now and I suspect my wires are about shot.

A ground will make it seem like the battery is dead when starting. Well, the main ground at least. Other minor grounds in the harness that go to sensors and such will do some very strange things.

[andrewm]

I've done a full tune up except wires, which are on the plan here shortly - but I can't imagine them causing this.

[jlevie]

The behavior of the econometer suggests fuel starvation. The meter is driven by a signal proportional to injector pulse width. Thus it's low reading is a sign that the DME is having to hold the injectors open way longer than normal.

Change the fuel filter and run the fuel pressure and delivery tests in the Bentley. That will tell if there is a pump or FPR problem. Then pull the pump & sensor from the tank and stir the bottom of the tank with stick while using a penlight to see into the tank. A layer of rust sediment in the tank can get stirred up while driving, collect on the inlet screen of the pump, and starve the engine. Suction will hold the rust in place until the car is parked for a while and the rust settles out.

[Exodus_2pt0]

A layer of rust sediment in the tank can get stirred up while driving, collect on the inlet screen of the pump, and starve the engine. Suction will hold the rust in place until the car is parked for a while and the rust settles out.

Kinda like the old ping pong ball with a small hole in it in the gas tank trick.

[andrewm]

Interesting - I already changed the fuel filter, I can get a fuel pressure tester and check it out. I had not thought of the fuel tank...I will check that. thanks