Help With Diagnosing This Problem

[bretamo]

I'm having trouble diagnosing a problem and need your help or advise in how to troubleshoot the issue.

Symptoms: The car severely trembles or shutters when the motor is under load. The shutter is a rapid shutter that does not go away as the car is in motion and advances through its RPMs.

It started after I ventured through a four way stop sign and accelerated to the next stop light. At that next stop light I felt the car shake more than normal when I depressed the the clutch and waited for the light to change. When it changed and I pulled through the intersection the thing just shuttered at the pace of a machine gun. I limped her home by slowly getting her up to speed, and then did a "coast, short burst of acceleration, then coast again" routine until I got home. The car shuttered every time I accelerated.

Other Facts:
- About 1500 miles ago I bolted on FR GT-40 heads, CompCams conversion Rocker studs, CompCam 1.60 Steel Rocker Arms, harded steel pushrods, Cobra upper and lower intake, 65mm TB, Summit Racing Fuel Pump 190lph, Underdrive Pulleys, and a new TPS set at .99v.

- I have not pulled valve covers to check rocker arms since the bolt-ons 1500 miles ago. There are no unusual sounds as the engine idles (no rattles or clanking).

- No noticable vaccuum leaks, as I have used the hearing test (hose to the ear), and sprayed starter fluid around all fittings and hoses (yes I know this could cause flame if a spark hit it).

- Pulled codes, and it passed (111), and it produces no intermittent codes.

- Engine starts fine, no smoke, sounds great, and runs through the RPMs in neutral without causing a huge shutter like it does under load. However, at idle the car does shake a bit more than it had prior to the problem emerging.

- When accelerating through the RPMS in neutral with no load, the shutter is nearly unnoticable (I'd say it is only slightly noticable).

- Cleaned the MAF sensor after the problem began; no improvement.

- Timing is set at 12 degrees without the spout, and the timing mark is stable (it does not jump around).

- Oil pressure and water temperature readings are fine.

- The shutter feels like its originates on the right side of the car. Visualize yourself in the driver seat and your motor is rotating like a wheel spinning clockwise in the engine bay. That imaginary wheel in the engine bay feels like it is way out of balances and tugs the car down and to the right.

Here have been my novice thoughts since this happened:

- Did I break a right motor mount, does a motor mount break cause the car to tremble and shake when under load?
- Is a clutch or transmission failure causing the car to tremble when under load, and could that cause the car to shake more than normal when the clutch is depressed or the car is in neutral?
- Do I have a rouge vaccuum leak that I just cannot detect?
- Is there something wrong with the internals of the engine?
- Is there a problem with the computer or any of the car's sensors; could there be a problem that would not be detected by a code reader?


Expert Mustang enthusiasts, please help by posting your thoughts.

Thank you for any help!

 

[HISSIN50]

I'd run a cylinder balance test. It sounds like one pot isnt firing - it's not super noticable with no load or while idling/revving with the car stopped (esp if the car's a little cammy). Once you get under load is when you'd feel it. It could be as simple as a plug wire that popped off or a bad plug.

That's where I'd start at least.

Good luck.

 

[bretamo]

Thanks, Hissin50.

The car's cam is stock (is that what you mean by "a little cammy"?).

I'll begin by checking the wires and plugs like you suggest.

But.....what if.....connections are good and the plugs are all firing. What are your next thoughts?

Thanks again.

 

[HISSIN50]

Thanks, Hissin50.

The car's cam is stock (is that what you mean by "a little cammy"?).

I'll begin by checking the wires and plugs like you suggest.

But.....what if.....connections are good and the plugs are all firing. What are your next thoughts?

Thanks again.

The CBT should help narrow down which cylinder isnt firing, if it's not a random misfire (the latter is not likely IMHO).

What I'd do then is: pull the plug and check it over and swap it. While it's out, check compression real quick (takes 30 seconds to do one cylinder). Then I put the plug and wire back on and put an inductive timing light back on the wire and make sure it's firing (as demonstrated by the inductive timing light showing consistant flashes). Then I'd put a noid light on the injector to ensure that there's juice reaching the injector (injectors get key-on constant 12 volts and the ground is what the computer modulates to fire the injectors).

There's a good chance that those checks (should take 10-15 minutes) could find the issue.

Good luck.