So, since I built the top end of the 5.0 in my truck, I have had a random engine shimmy/shudder/shake/whatever. Ive been trying to track down the cause but have been unsuccessful. Here is a video of another engine that looks to have the same "shudder" mine does:


Have any of you ever seen anything like this? It is completely random and inconsistent. Some shakes are more violent than other. Whenever the engine shudders the rpms dont seem to change nor does the exhaust note change.

Engine mods: tfs 170 61cc track heat heads (thermactor air function turned off in tune), custom ground ed curtis cam, 1.6 probe roller rockers, moss ported lower intake, jba shorty headers, magnaflow y-pipe, dronemaster 40, 3:73 frpp gears. Also turned off in tune: knock sensor function, and egr function. Truck put down 225/267 to the wheels. Poopy numbers if you ask me but when you consider the 205/275 they came with from the factory (to the flywheel) I guess its not terrible.

Some more details and things that have been suggested on other forums:

Fuel pump/fuel trims: This would have shown up in the A/F on the dyno, no?

Spark/miss: New plugs (gapped at .050) and wires, new tfi and coil, original distributor.

Motor mounts: Maybe?

Bad balancer: Not likely from a reliable source (holla at my boy qdeezie).

EGR: Still leaking exhaust gases into upper, despite being turned off in computer. Thoughts?

Anyway, trying to eradicate this engine shudder but havent been able to. Ideas please? No codes, cylinder balance test passes on first go.

If I dont have it figured out by mid-May then its going back to the tuner, and maybe he can uncover something with his data logs. In the mean time, Im bored and like tinkering, so lets figure this out =).

Thanks fellas.

 

Try a vacuum gauge. That would possibly tell you where it's coming from. My first thought would be valve spring but that's just a wild guess. vac test should identify that.

 

I'm assuming this is at idle right (just like the video)? Mine is going the same thing (not as bad). It's likely just the Cam doing it, but I would do like Chris said and check with a vacuum gauge.

 

Okay. Why would a valve spring cause this? I thought (hoped) it could just be the cam but I emailed Ed and he said likely not lol. Also, what do you make of these dyno numbers LOCO?

 

Have you sat an watched it for a few minutes at a time too see if there's any rhythm to it?

What are the specs of the new cam? If it's a higher lift did you put on stiffer valve springs?

Have you checked the adjustment of the rockers?

 

No consistency or rhyth to it. I was told the track heat heads had a seat pressure of around 150#, and since my truck wasnt going to be spun into the 6s and 7s they would be fine. Hopefully I wasnt let astray. I was told that by a performance engine builder. Havent looked at rockers since we set the valve lash during the build. Did it per instructions on the cam card.

 

Look at your dyno sheet and compare mine if you like.



I just think you have too big of heads (likely low static compression ratio) to be making good power unless you add a turbo or supercharger.

 

What are the specs of the cam? Lift, duration, and lsa ?

 

He sent me a PM about last month with the specs, Here they are:

Unless you want mine?

 

You are most likely right. The tuner at Finish Line Automotive in Denver told me that if I was already at low compression in MO, I'm even lower up here. Oops. I still would like to get rid of this shudder. Oh well, going back to my tuner in MO on May 15, if he can't figure it out using his experience or the data logs I'll just have to accept it.