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I am wondering what the symptoms of a bent crank, or an out of round
crank might be.
I have two 89 4.0 engines, so all the parts are compatible. So I was
going to start swapping sensors, coil, and other parts to see if I can
move the problem from one jeep to the other.
Again the problem is after 15 minutes of driving, the engine loses all
power at 3000 rpms and above. bumping and farting until I let off the
gas down to 2500 rpms.
It doesnt matter if I stop the engine and restart it.
It doesnt matter if it is under load or not.
After it sits for a couple of hours, everything is fine until it is
running for 15 minutes.
Any thoughts on where to start?
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bad O2 sensor or stuck EGR, bad fuel pump relay or pump itself is bad/overheating.
bent crank would cause horrible vibration at all RPMs and likely rubbing noise in the bellhousing. front pulley would also wobble & probably throw belt.
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I saw that once on a chevy pickup--it was a bad wire harness that ran close to the exhaust manifold and when heated up one of the wires separated from expansion.
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It didnt seem to do it before I was taking a bolt off the exhaust, and
the vibrations caused the old O2 sensor to explode....lesson
learned....take out O2 sensors before using an impact on the exhaust.
I put a new bosche O2 sensor in it when the problem started.
Fuel pump is a Corvette external fuel pump and the pressure and drip
down tests seem to rule that out. If the pressure is within specs while
this is happening (on the valve on the fuel rail).
Since your description of the crank is not happening, It is great up
until the engine runs for a bit. I think the Hesco harmonic balance TPS
is probably out of round by 10/1000....and I can take it off and let my
machinist friend get it within specs. I had two problems with this
puppy. The CPS they sent with it was damaged by thier guy setting it for
the harmonic balance puller. I had to go to the junkyard, get my own and
take the mount off.
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check exhaust back pressure , could have a catalytic converter going bad, works ok cold but when warmed up after running a while restricts exhaust
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yeah, if you're CPS isn't round you'll have some issues with timing especially when it warms up, the gap may expand. I'm not familiar with the Hesco unit but that'd be the first thing to check being it controls timing and may be retarding to base timing when warm.
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The hesco uses the stock CPSensor with the mounting flange removed and
the rubber ground off until it fits into an aluminum mount. The aluminum
mount goes where the timing marks are.
The Harmonic balancer is replaced with the Hesco harmonic balancer,
which looks like a square tooth gear. Then you set the CPS at .010
But we found that the unit is out of round, what we had to do was
measure it around, and set it so they all fall within .005 and .010
It is a small hassle to remove it, as I have to remove the radiator etc
I was going to have my friend (a machinist) round the harmonic balancer
to .001 of round.
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