Idle shudder

[8973]

**UPDATE BELOW**

Howdy.

I have an 89 F-250 7.3 5 speed. 180k. Well maintained (additive, SCAs checked, all the good stuff I learned here). Pump has maybe 50k on, injectors unknown. Not sure on the fuel filter, but safe to say it's under 10k.

I am getting a weird shudder at idle. It comes and goes, and has for some time, but was pretty bad last day or two.
Basically, if I let it idle it starts to shudder- on and off, rather violently. It feels a little like it's starving for fuel, but I could be way off. As soon as I give it throttle it smooths right out. Even if I just touch the pedal it stops. Starts, stops, runs fine otherwise.

At first I thought it was a rusted pick up tube. I had an intermittent surge, especially around corners. I replaced the tank and sender around 3k miles ago, and everything was ok. Surge is still gone, but the shudder is coming back.

I replaced the return lines/caps/clamps yesterday (which it needed) and there was no change; or it possibly got worse. I ran it up the highway for about 20 minutes, and after it shook as bad as ever.

Could it have been the return lines, and it just needs a little more time? Am I being too optimistic? What else would cause this?

 

[Late_99_psd]

Sounds like you may be getting air in the system somewhere.

 

[gunz]

How does it start in the morning when the motor is cold? Fire right up or does it have to turn over a few times?

 

[8973]

Starts pretty good. Cranks for a few seconds, then fires. Lately if it sat for a day or two it would fire then die, then crank a while before firing again. Second time it would run fine. I chaulked this up to bad return lines, hence replacing them yesterday.

Apart from the start/stall after sitting issue, it has been starting as good as ever.

 

[funnyman06]

your getting air ( probably old return lines) in the system. Track down your air leak and it will probably go away.

 

[gonecrazyi]

Its a 5 speed correct? That's exactly the way mine sounded when the flywheel started to go. A new luk cliche and flywheel kit fixed it.

 

[8973]

Its a 5 speed correct? That's exactly the way mine sounded when the flywheel started to go. A new luk cliche and flywheel kit fixed it.

Yeahhh, not exactly what I wanted to hear, but it makes sense. Thanks.

Any way to confirm that? How ugly is it when it fails completely?

 

[hesutton]

You've got to determine if the shutter is a miss in the engine or something else like the flywheel. What you are discribing leds me toward a miss. But, either way, you need to know which one is the shutter.

Are you sure your injectors are in good shape. Have you tried to crack the injector lines one at a time while the engine idles to see if it gets worse or stays the same. Are any of the caps/lines wet with diesel? Do you smell diesel when you are under the hood? Does it ever shutter at any other condition than idle?

Honestly it really just sounds like a bad air leak and nothing serious.

Heath

 

[8973]

You've got to determine if the shutter is a miss in the engine or something else like the flywheel. What you are discribing leds me toward a miss. But, either way, you need to know which one is the shutter.

Are you sure your injectors are in good shape.
Not really, no.
Have you tried to crack the injector lines one at a time while the engine idles to see if it gets worse or stays the same.
Hopefully going to try this tomorrow
Are any of the caps/lines wet with diesel? Do you smell diesel when you are under the hood? Does it ever shutter at any other condition than idle?
No x3

Honestly it really just sounds like a bad air leak and nothing serious.
*crosses fingers*

Heath

Thanks. Anyone care to give me the low down (or any links) on how to check for air via the clear hose method? What size hose should I get?

 

[hesutton]

Never tried the clear hose method personally. But my understanding is you replace the return hose from the #1 injector to the filter head with clear tube and watch for air bubbles as it idles.

Another way that I use is to have someone crank the engine (remove the wire from the fuel solenoid on the IP 1st so it won't start). When cranking starts, open the schraider valve on the filter head. If air or a mix of air and fuel comes out of the valve, you have an air leak.

Heath

 

[Dsl_Dog_Treat]

Since the injectors are unknown, sounds likes a few of the injectors may be leakers causing erratic idle and diffcult starts.

 

[8973]

Its a 5 speed correct? That's exactly the way mine sounded when the flywheel started to go. A new luk cliche and flywheel kit fixed it.

WINNAR!

Did a flywheel/clutch kit and the shudder is gone.

I spoke to a clever mechanic friend of mine, told him my specific symptoms, and this is what clinched it: It would never shudder cold. I could let it warm up for 15 minutes in the morning and not a lick of shudder. Drive it for 20 minutes, it would begin to shudder almost as soon as you stop. Apparently when the tranny fluid is cold it would place enough load on the flywheel to keep it smooth. When the fluid warmed up the transmission would almost freewheel, so to speak, and allow the flywheel to shudder.

Thanks Crazy.

 

[8973]

D'oh. Double post.

 

[icanfixall]

Glad to learn you got it fixed. This is what this forum is all about. Its the ehlping of others determine whats wrong with their rigs without the dealer involvement. Those crooks can be expensive.

 

[CaptTom]

WOW!!

Excellent diagnosis!

Thanks for sharing that. I'd still be fighting the fuel system.