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Dr. Hamman
Dr. Hamman, Automotive Engineer
Category: Car
Satisfied Customers: 5929
Experience:  30 years experience, Repairing, building, & designing, automobiles.
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75,000 original miles. Runs great on the open road. Will idle perfect for 10 minutes. Then

Customer Question

75,000 original miles. Runs great on the open road. Will idle perfect for 10 minutes. Then starts to sputter and stall. Give it a shot of wd40 and it will fire right back up and idle. The 5-10 minutes later, it does it again.
Submitted: 1 year ago.
Category: Car
Expert:  Edward replied 1 year ago.

Eclayton4 :

Hello and thanks for your question. My name is Eddie and I will do all I can to help. Sounds like a fuel pressure issue to me, I see you have replaced some fuel system components, did you replace the fuel pump itself by chance?

Customer :

Not yet. Its a bigger job. The car never stops or sputters on the open road. I didn't think it was the fuel pump

Eclayton4 :

So as long as your driving it down the highway, you never have this issue? just when it's idling parked?

Customer :

Right. I use the car as a taxi, so there is a lot of idling time. It doesn't do it all the time when iding.

Eclayton4 :

OK, Is the check engine light currently on by chance?

Customer :

No. and checked to see if it had an code anyways. But there are no codes of any kind showing.

Eclayton4 :

Interesting, First thing I would do, is install a mechanical fuel pressure gauge on the fuel rail, Let it idle and watch the fuel pressure, If the fuel pressure drops when the engine starts to stumble, I feel certain it will be the fuel pump itself (Can't rule out a relay or fuel pump circuit but usually that's constant) With no codes and it being intermittant, have to start narrowing it down. It sounds like it's running out of fuel to me. I know this sounds elementary, but you are sure the air filter isn't stopped up correct?

Customer :

Fuel filt night it started in againer, regulator, mass airflow sensor done yesterday. fuel pressure is fine. went 10 hours without a problem. 11o,clock last

Customer :

sorry, 11 o'clock last night it started in again.

Eclayton4 :

Alright, Let me opt out, I really don't have a clear cut answer for you on this one, let me open the question back up and if another expert has a suggest they can then respond. Thank you. I will research this and if I can add anything I will.

Customer :

ok

Customer :

still here waiting

Expert:  Dr. Hamman replied 1 year ago.

Hi, I am a professional certified mechanic, with an engineering background, and 35+ years experience. I will do my best to assist you. Also keep in mind I don't know if you are a pro or a novice, so feel free to add any additional info at any time.



Hi, I work on these LT1 5.7L, and the L99 4.3L V8's they used in these cars a lot. If the fuel pump is failing when it does, just turn the ignition off, and back on quickly and listen for the fuel pump. You can actually hear it if it is operating like it should. Normally on one of these Roadmaster's when the fuel pump fails it will idle all day, and the pump will act up normally while driving down the road, then the engine will die. Once that happens it wont start no matter what for at least an hour. Then it will fire right back up and run perfect. The cycle repeats over and over, and it will take longer for it to restart, and the pump eventually fails.

There are a few inherent problems in this model that cause the symptoms you are having. One is a ground connection that attached to the front of the drivers side cylinder head. This ground is where several critical ground wires from the ECU, and other parts of the electrical system grounds. For experienced electrical techs that have worked on these a lot Roadmasters are well known for loosing connection here, and it causes the engine to die. Normally the engine will restart. What happens is where the electrical connector crimps to the wire the connection starts going bad. The solution is to locate this bundle of ground wires, and clean them, then solder the connectors to the wire, and reattach it all. Look for the ignition coil bolted to the front of the drivers side cylinder heads, the ground cluster normally attaches at the base of one of the coil mounting bolts if it is all still like it was out of the factory. You will probably have to remove the electric emissions air pump to get to the ground.

Other than this problem the optispark distributors, and ignition modules are bad about failing. The opti uses a Mitsubishi optical trigger, and they get dirty, and have more trouble triggering at lower speeds, so the engine dies. There is no definitive test for this. The ignition module is also suspect, and can cause this problem. It is riveted to a bracket attached to the ignition coil on the front of the drivers side cylinder head. The opti, and the ign module, or the ground connection will not register any trouble code. If it was mine I would start off with the ground connection. And make sure the optispark distributor has it's two vacuum hoses attached. The earlier opti spark didn’t have vacuum hoses, and water would find its way inside, along with and crud the water had in it. This would eventually crud up the optics on the opti spark, and cause misfires. These hoses are on the drivers side, one taps into the duct from the throttle body to the MAF, the other taps into the intake manifold, drivers side about halfway back, on the side. One last thing is if you replace the optispark distributor, the early and late opti units do not interchange, and ebay is your best price source, search for “optispark”. Go over all of this and if you have any more questions at all, I am here to help. Good luck with it, have a great day, and Thanks for using Just Answer.


I do not get paid for my work unless you rate at 3 to 5 Smiley Faces or Stars, a bonus is always greatly appreciated. If the answer is not clear, let me know what additional help you need, and I will be happy to assist you further.


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