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Those balancers are easy to break with the wrong type puller like a claw type. You definitely have to use a harmonic balancer puller on them. I'd say someone used a claw type puller on it before and it finally gave in to a hairline crack. It makes sense as it was firing late to the point the the exhaust valves were opening while combustion was still going on. It's not going to throw a code because the crank sensor is still reading the vanes.
I would suspect the cats but that would throw an O2 code. I've seen timing issues and lean conditions glow the manifolds before. I had an old 1964 Ford 30 years ago do that. I scratched my head for a long time.
Sadly, I think the problem may be more frequent than realized. The problem I saw with mine didn't look like the fault of a puller or it's misuse. The keyway on the balancer was stretched out. You could see where it had stretched to about three times the width of the key. Once it had stretched to a certain point the balancer broke. This truck must have been running less than 100% for quite some time.
We suspected the cats, fuel pressure, etc., etc. I believe pretty much every possible suspect was checked and/or replaced up to the point where we found the bad balancer. The truck was even taken to a Ford dealership who couldn't find the issue. Their suspicion was the Cats were clogged. I almost gave up at this point since we'd already disconnected the exhaust at the manifolds to test.
I have a friend that's a great mechanic. He said from the beginning he suspected a mechanical timing issue, Timing chain, crank sensor, etc. But Ignored the crank sensor since it had been replaced. I guess I should have listened to him in the beginning since I found the issue when installing a new timing set.
I will say this.. The timing set had almost zero slack at 280k miles. I was impressed.
It was the harmonic balancer. The keyway widened and then broke. The crank sensor was picking up the wheel in the wrong place as a result. I swapped the balancer and the truck runs like new.
Knew it wasn't cats because it had the same symptoms with the exhaust disconnected at the manifolds. Was one of the first things we checked.
Thankyou!!! For posting these results, I have been through this whole truck trying to figure out the problem.. All along I had no trouble codes either..After reading this thread I crawled under my truck and sure enough the harmonic balancer would rotate left to right about a 1/4 inch!! Without ever turning the crank! I pulled the holding bolt and the balancer slid right off.. I could then see down in the keyway that half the key slot was double the width from the original size....Can't thank you enough for Taking the time to post your results.I'm trying to get a new balancer now.
Harmonic balancer broke sheared off in two pieces right at the crank seal, motor ran ruff had no power and both exhaust manifolds glowing red after about 5 min of run time. I was ordering new cats because that's usually the first thing that comes to mind that there's blockage read this forum stoped my order checked the balancer broke so thank you
What was causing the balancers to break? Never heard of this
Me neither working on this truck for my uncle found this forum today read it checked mine and broke maybe it's a maichine fit and it's not as tight as they should be and over time vibration causes it.
Wow I just found this tonight while trying to make sense of this 98 F150. No codes but no power along with occasional backfire. I pulled the intakes to check out gaskets and it needed the lowers badly. While it made a noticeable improvement, it still was sick. So tonight after reading this, I pulled balancer off and sure enough the keyway is twice the width it should be.
12-07-2012, 01:08 AM
