1994 GMC Jimmy - 4.3L Fuel Pressure

[Tim Martin]

Got a 94 Jimmy here with a 4.3L (W) engine. Starts hard, runs very rough once it does start. Has no power, acts like its out of gas.

Fuel pressure is rather strange. At first when key is turned on the pressure goes to 60psi. As soon as pump stops running it drops to 30psi. While the engine runs it is 60psi. Testing it seemed like the fuel pressure regulator is bad so I installed a new fuel metering assembly as parts place said this one was under warranty from a previous installation. Same result. Listened with electronic ears inside gas tank to see if I could hear fuel pump pulsator leaking. Nothing. Is there a check valve in fuel pump that could be bad? Or is there something else I am missing?

[David Brown]

I Would Make Sure All Connections To The Fuel Injector/s Before Taking The Fuel Pump Any Further. We Have Had The Connection To The Injector Outside The Intake Eat Our Lunch. There Should Be TSB's About This Connection.

[steven kiser]

pull the 02's and see how it runs. these trucks eat cat's. i've run into so many that when one comes into the shop for driveability issues i almost automatically take pressure readings. i go through the 02's as a rule. i dislike the drill and screw method and i've run into a mild explosion one time when the issue was a stuck injector and the introduction of air into the front pipe through the hole followed by a mig arc "lit up my life" i was looking for debbie boone. smashing my pumpkin on the lift arm put me in Sherwood Forest for a while. i'm surprised that i wasn't approached by a representative from the actors guild because of all the entertainment i supplied.

[Tim Martin]

This vehicle is back. Again. This time it will not start when ambient temperature is below about 50 degrees. It can set in my warm shop overnight, come morning it will fire right up. If I set it outside overnight, it is a no start with 55psi of fuel pressure and good spark on every hole. No trouble codes, engine runs fine once it starts. What am I missing on this crank? Has new fuel pump, new injector assembly, new plugs, cap, rotor, ignition module.

[GFORCEAUTO]

Tim,
With the fuel pressure bleading off down to 30 psi is a classic indicator of a bad fuel pump. But I would quickly remove the upper part of the intake manifold and look to see if the fuel pressure regulator is leaking off the side of the injector. Also while you have it off check the plastic fuel lines that go to the injector I have seen them crack and leak fuel in to the upper part of the intake. But I would bet that you have a weak fuel pump. Get the lab scope out and check the fuel pump motors pattern if you have all the correct tools. The W engines were kinda picky on fuel pressure if it's slightly low ... low power, hard start ,no start. Oh and get a Delphi pump no remans !! Or you be doing it again for free!

Matt

[liljoe]

Sounds like a coil problem to me. Seen lots of these on lots of diff GM cars and trucks, usually around this time of year too.

[brianp87]

injector and hoses alot of problems?

[liljoe]

Might want to check the coolant temp reading on the scanner when it won't start and see if it is reading too warm, this would cause too little pulse width to start a cold engine. If it is OK, I would put a light by the coil and warm it up a bit and see if it starts. I would lean towards the coil.

[brianp87]

add fuel from an outside source and try it

[Tim Martin]

This thing will start right off with just a sniff of ether in the morning. Rest of the day it is fine. Starts ok once it is started in the morning.

Had not thought of the coil. Will check it.

Thanks for the ideas guys!

[steven kiser]

just a quick toss here. a worn timing chain will cause symptoms like this.

[GFORCEAUTO]

CHECK THE BLUE AND RED WIRES TO THE INJECTOR ALSO HAD ONE OF THOSE BREAK INSIDE INTAKE

[Tim Martin]

CHECK THE BLUE AND RED WIRES TO THE INJECTOR ALSO HAD ONE OF THOSE BREAK INSIDE INTAKE

Did that one start intermittantly like this one does?

[GFORCEAUTO]

The one we had was laking power and needed more fuel and we found that the injector connector wires were weak at the connector causing a poor connection when cold ...tempature cold . Alot of those had issues with the pickup coil inside the distributor. We replaced the entire distributor on a 4.3L/ W engines but I really think you have a bad fuel pump ... has happened to us bad right out of the box. Thats why we only use delphi pumps.
Email me direct at gforceauto@scbglobal.net
hope this helps ya

[Tim Martin]

You mentioned the pickup coil inside the distributor. I had thought that if they are not working properly, the engine will not run at all. Or am I wrong?

[steven kiser]

back to basics guys. engine needs fuel, compression, ignition, exhaust to run. i have read we have fuel, spark, and exhaust. what's the compression cold? pull the distributer cap and walk crank back and forth to see how much movement is needed before rotor moves. just to be specific here the pump pressurizing to 60 then bleeding to 30 isn't an issue. what is the spark amp? weak spark will most defiantly cause an issue like this. we'll put a spark tester in line at the plug and see how bright it is. if it's just a blip you probably have a bad coil. ignition wires will cause this issue. it's time to stop pulling your hair out. never assume the installed parts are good. i've seen more that my fair share of failed replacement parts. the ignition coil has to produce a high voltage spark for this to run. if the spark isn't jumping at least 1/2 an inch and bright the coil is probably weak. you could also have a helper grab the shaft of a long screw driver that's stuck in the plug wire while your cranking it. if it doesn't blow his socks off the coil is bad. at least it'll make you smile.

[Tim Martin]

Finally got this set a wheels figured out an fixed. It was the fuel pump pulsator. I installed new fuel pump. New pump instructions said not to use a pulsator. they even supplied a hose and clamps. Also put in a new fuel filter. Engine started right up and runs fine. I know that I learned alot in this job. What was so puzzling was the fuel pressure it did have. It would go up to 65 psi, then drop back to about 35 psi. I should a went on my original hunch an dropped the tank instead of all the other stuff I chased.

Thanks guys for all the ideas.

[steven kiser]

thanks for posting the fix although i don't see how it was the pulsator when there was 60 psi at crank.

[Tim Martin]

As soon as the fuel pump stopped running the pressure dropped to 30 or so. When I opened up the tank, the pulsator was ruptured. No question what the problem was.

[brianp87]

add fuel from an outside source and try it

Just saying that when u said u added fuel and it was ok then that was a good idea of were to look