1996 Engine Shake when not FULLY warmed up

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Hello All,

I have '96 F350 5-speed that will shake quite a bit in the higher rpms (>1500) when its not fully warmed up. I can have the block heater on at night, let her idle for 10+ minutes and it will still shake badly. It depends on how I use the clutch as well. If I lead with the engine rpms a bit it seems to help. At idle it sounds fine, a bit of a "psst" every 10th-20th revolution or so

I have an AutoEnginuity scanner and it passes both buzz test and cylinder contribution tests, but the cylinder contribution test will only perform when engine oil temps are > 170 degrees, and by that time the engine is running perfectly.

I have two ideas, please help me confirm or rule out either:

1. 2 piece flywheel going bad. Expensive repair and does it make sense that it goes away when the engine is warmed up?

2. Injector sticking/misfiring until its nice and warm, maybe an old o-ring that expands a bit when warm and creates a good seal? I'm not sure how to figure out which injector it is, I'm guessing infared or some other heat sensor on the exhaust manifold to see if any cylinder is colder than the others.

I live about 2 blocks from a ford dealer, but i'm reluctant to take it there, this truck was bought on a budget and while I want to make it run for a long time, i would like to do as much of it myself as possible.

Thanks for reading, I really appreciate this whole community.

[red97]

first off how many miles does it have. I replaced the o-rings at 180,000. If there is oil in your fuel filter, shure bet that the o-rings are bad. Get the polymere set at international. Ford dealer cost almost twice as much. You need to let it warm up to full running temp. I let mine run for at least 30min before I move it. even in the summer. Diesels atr cranky *****es. It can't be to cold or to hot. good luck

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almost 350k on the truck, but only about 150k on the engine. No evidence of oil in fuel filter at all.

I've just been letting her warm up for a long time and taking it easy for the first 10 miles or so. I'm just worried that the shaking will harm the rest of the engine/body of the truck. Also, while it has the shaking symptoms, it has much reduced power.

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Ok guys and gals,

new symptom: When i'm driving along and i push in the clutch and take my foot off the gas, the engine drops down to below normal idle speed and chuga-chuga-chugs along for a bit before regaining normal idle. I noticed that the voltage (battery meter, i'm going to test it with autoenginuity soon) drops as well and hits a low point right before the engine starts chuggin. Its almost as if there is something shorted out briefly and it sets off a reaction in the engine.

I originally though that it was the engine chugging that wasn't turning the alternator enough to produce the same voltage, but it just dips down for a brief second then goes back to normal, even while the engine is still doing the chuga-chuga-chuga...

I think i'm going to have a look under my valve covers soon. Anything I should look for in particular besides melted wiring?

Thanks again for looking.

[Farmboy444]

the only time i saw one of these trucks with those symptoms it was the injectors, but they had 350k on them, but mileage means nothing, its all in the maint. My voltage drops a good bit from here to there but that was a bad alt and nothing as bad as your symptoms. Good Luck

[special_ed1977]

fuel bleed down. maybe the water separater. or bad injector o rings

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Thanks for the replys, i have new o-rings on the way. I'm going to take off the valve covers this week and replace glow plugs and o-rings and inspect for any electrical damage too. How would one diagnose the water separator?

[special_ed1977]

there should be a piece of steel tubing coming from it running down the front of the engine. the other thing you could do is check for diesel in your engine valley. the separater is right behind the fuel filter on top of the engine. that really all there is to it either leaks on the ground or in the valley.

[blimp]

I'm now getting an injector fault when I run a buzz test, p1276, Cylinder 6: High to Low Side Open. I have the valve cover off and all the connections look good. I tested for continuity in the under valve cover harness and it seems fine. I have a 'new' remanufactured IDM because i was getting an IDM failure code. My next step is to try and test continuity all the way back to the IDM, and if that is solid i'm going to replace the injector...

Thanks for reading, i hate going to bed frustrated.

[4everlearning]

Hope you get it. Let us know if you need anymore help.