For the longest time I thought my truck had a caliper or two that weren't fully releasing causing my truck to shake at 60 mph+. I was right and replaced both front calipers and put in new pads, but there was more to the story....

As it turned out an injector (#2) was misfiring above 60 mph. After a visit to PSE to confirm, I replaced the #2 injector and it ran good on the road test, but I was back to square one not long after. The misfiring wasn't as bad, but it's still there. (the other 7 were VERY healthy as proven with the FICM compensation off)

Things I tested/fixed/replaced:

-If while I'm driving I let off the accelerator, the misfire obviously stops. As soon as I ease back into it, it starts up again. So I know for sure it's misfiring somehow.

-I did some reading and found that the FICM logic board can burn up causing the situation I'm experiencing. I had a spare FICM, so I swapped logic boards and the truck started night and day better (started like crap before, but ran nonetheless), but the misfire at 60 mph+ was still there. I also made sure the connectors were fully seated.

-I checked the harnesses around injector #2 and wrapped them in some rubber insulation in case they were chaffing against the intake manifold somehow. Again, to no avail...

-I unplugged the ICP sensor and drove on the freeway, but again no Bueno.

-I tried unplugging the EBPS, but since my strategy is non-inferred, my truck wouldn't boost properly and I wasn't able to complete the test. (I'm starting to suspect that it may be playing a role somehow.)

The truck runs awesome at anything below 60 mph, the injectors sound happy and the truck accelerates without a problem. I just can't figure out why it would misfire the truck at highway speeds. It gets down the highway just fine, it just rattles the cab and has been doing so for some time now.

What am I missing?

 

Run a cylinder contribution test and see if it's actually a cylinder dropping. If you are not seeing anything there. Try driving it at the shake apart speed of 60 then apply light brake pedal, just enough to kick out of lockup. If shake goes away you may be looking at a trans issue. Converter clutch shutter feels about like a cylinder misfire.

 

Interesting....

On my 7.3 Excursion I could feel the converter shaking itself and the trans before it was replaced February 2006 due to a bad one way clutch.

I'll see what it does as lunch time.

In case this isn't the issue, any other thoughts?

 

I have never seen a 4R100 with converter shudder. I'm not saying it can't happen, but I'd be very surprised if it was converter shudder. The 4R70W is well known for converter shudder, and it has some design problems that cause that. The 4R100 did not have that problem.

Tapping the brake to turn off the converter lockup also puts the engine in a different operating condition, and that can change what's happening in the engine.

 

Possible to run IDS or AE contribution while driving 60 mph?

Letting off at 60 and vibration goes away? If you accelerate does the vibration go away?

Could still be driveshaft related which is what my thoughts would lean towards or pushrod related.

Josh

 

Run a compression test. If there are any problems with coolant intrusion into a cylinder (either previous or now) such as an egr cooler, it usually shows up on cylinder 2 or 8. It bends a rod, not letting the compression be uniform throughout.

 

The only other things I can think of is if it's not a wire chafing issue, would be injector cup ball oring or lifter trunion wearing down. If you've proven out electrical then you may have a high pressure Leak from the ball cup seal. All scanners I've ever used can never pick up actual mechanical failures. Does yours point you towards which cylinder is weak?

 

Thanks for your responses so far

I thought it might've been the converter on the 7.3, but all I know was that it would shake real bad before it went into overdrive. It never did it when the trans was replaced.

It'd be interesting to find out if the IDS could run the power balance or contribution test while at 60+. I know the AE can't do it.

It starts at 60 mph and gets worse running 65-80 mph. It's still there, but lightens up sometimes if I accelerate and if I let off without tapping the brakes it's still there.

I don't hear any signs of a pushrod being bent through the exhaust or intake and I the thought of the driveshaft also came to mind. Seems more engine related though, I could be wrong.

I'll see if I can get my hands on an IDS to run a compression test. If I'm not mistaken, this is the test that delays the engine starting for approximately 10 seconds correct?

The thought of a HPO leak at the nipple cup is one that occurred to me. I have the tool and the orings to do it, but I couldn't find the O-rings and needed to get the truck back together to get to work in the morning. I plan on hooking up the AE and watching the ICP actual vs. desired to see if I indeed I have a leak. I'll more than likely pull it again anyhow and replace the O-rings as a precaution.

I haven't run a compression test yet, but injector #2 is the one that showed as weak. When we ran a power balance with FICM compensation off, we turned off each injector individually for a 5-6 seconds, then turned them back on. Injector #2 is the only one that didn't come back up.

I checked around #2 for chaffing and insulated where I thought it would chaffed and didn't see anything.

While under the valve cover, how would I be able to tell if a lifter were bad or going bad?

 

If lifter bearings are going bad you will have slight to excessive pushrod play. It's tricky to test but can be done. I've always rotated engine over to compression stroke on the suspect cylinder and then checked pushrod travel by hand and feeler gauge. Check both intake and exhaust side. Also make sure the valve tip bridges are in place. I have seen some that someone didn't have on both intake or exhaust valves. Causing it to only open one of the 2 valves.

 

would these not be more of an all the time problem?

try putting the truck in gear 1 or 2 and run it at the same RPM you would at 60 MPH in drive and see if the problem persists. im starting to think it may be something drive line related. (carrier bearing, drive shaft etc..)

 

I think before we meander off into the abyss, there's a lot of missing information here. No mention of any warning indicators, codes, fuel pressure, relative compression and how far off the enhanced injector balance test actually was. I mention all of this because I got the impression that you have, or have access to, a Ford IDS?

 

Did this and no go, it doesn't shake or anything at all. Drives normally.


I have access to a Ford IDS, but it depends on how busy they are.

With regard to your questions:

-The only real warning signs that I got were that on occasion the pedal would be "hard". In other words, where I could previously and lightly depress the accelerator and the truck would go, it would take more and more pedal to get the truck to go. It eventually got to the point where the truck would start misfiring with normal in town driving. This was the day I had the IDS on the truck and injector #2 was found bad.

-I never got any codes no matter what test I run. KOEO, KOEO injector buzz, KOER. I drove the truck a total of 500 miles on a roadtrip with the issue and never got a code for anything, not even a pending code. What was strange was that while on the 4 hour journey, the issue cleared itself up for a good long while then came back once I got back in town.

-The injector balance test with FICM compensation off was reasonably flat with the exception of injector #2. We shut them off one by one for a few seconds each and #2 is the only one that didn't come back up or at the very least took it's time.

I'm supposed to meet up with a guy who works at a shop and run through a few things with the IDS. If he's not available, I'll see what I can accomplish with the AE.

 

I heard back and the relative compression test was good. They perform this test first on every vehicle before they go any further.

 

Have you dropped the driveshaft and physically checked for smooth movement on all joints. If you have one dry cup and a loose carrier it can send the shaft into a whip.

 

I would drop the rear drives shaft and run it in 4wd and see what happens.