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Matt
Matt, Engineer
Category: GM
Satisfied Customers: 20593
Experience:  Honors degree in Mechanical Engineering, worked 8 years as a Formula 1 engine engineer.
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Workhorse P32: I have a 2000 Workhorse P32 chassis (Winnebago

Customer Question

I have a 2000 Workhorse P32 chassis (Winnebago motor home) with a 7.4l Vortec, 78K miles, well maintained. I have a chirping sound when under a load and over 2K rpm. No chirp at idle or when cruising along...just when I lean into it...like to maintain speed while going up a slight grade. I've already changed the serpentine belt, idler and tensioner pulleys. Doesn't matter if engine is warm or cold. Could this be a camshaft position sensor issue?
Submitted: 7 months ago.
Category: GM
Expert:  Matt replied 7 months ago.
HelloThis could be an airleak after the airflow meter, any air dragged in here isn't 'seen' by the ECU and so not compensated for and can lean the engine out and can also allow the engine to rev up when not desired causing rough running.As its a mechanical fault it tends not to turn on the fault light and you can sometimes hear a 'hissing or squeaking' noise with the engine running. Check the hose clips for tightness and inspect the trunking for any cracks or splits and also all the vacuum system, the small bore pipes and fittings for cracks and missing parts. The best way to locate a leak is to have the engine running and warm and then spray lighter gas /propane around each joint in turn. If the engine rev's up you've found your leak.Now you might think that spraying lighter gas around a hot engine isn’t wise, however the flash /ignition point of gas is about 400°C so you need a naked flame or spark to set it off and I’ve used this method for many years without incident.Work your way through each possible joint one at a time and you should find it. I use a slightly flattenedpiece of brake pipe and some rubber hose from the can of lighter gas to provide a spraying 'wand' and allow a direct blast of gas into each area, especially those difficult to reach with large implements.
Customer: replied 7 months ago.
It's a very loud "chirp chirp chirp" that changes with RPMs and is only present when accelerating, not a hiss nor a squeal. Engine runs fine, no loss of performance.
Customer: replied 7 months ago.
Sprayed propane around every hose, tube and fitting. No change in engine speed whatsoever. Engine idles perfectly, never rough, and never suges.
Customer: replied 7 months ago.
Never surges*
Expert:  Matt replied 7 months ago.
OK in that case its worth checking for worn mountings -check the tightness of the engine and gearbox mounts and their condition - thisis best done by using a jack to take the weight of the engine off the mountsand seeing if any cracks or splits open up in the rubber.Also check thetightness of the mounts bolts
Customer: replied 7 months ago.
OK, I have a floor jack and will check the engine and gearbox mounts...
Expert:  Matt replied 7 months ago.
understood
Customer: replied 7 months ago.
Mounts are fine...
Expert:  Matt replied 7 months ago.
OKin that caseit would be worthwhile checking the propshaft either for a worn joint or the centre bearing is worn or its out of balance you can easily check for for any slack in the propshaft joints by twisting either half by hand and feeling for any play as there should be virtually none the centre bearingis quite loosely mounted so this can be moved normally but if you can run the car in gear with the wheels off the ground and then feel the centre bearing housing for vibration if there's any then consider replacing the unit and then look along the propshaft for any signs of a missing balance weight as these take the form of little 3/4" squares that are welded onto the shaft - as they are only tacked on they can sometimes come loose and be lost resulting in the shaft being out of balance - if a joint is worn this can also shake them loose so if a joint is replaced its good practice to have the shaft re-balanced afterwards
Customer: replied 7 months ago.
Wouldn't the propshaft chirp all the time, not just under acceleration?
Expert:  Matt replied 7 months ago.
hello not necessarily as there will be a rubber element to the prop that winds up under load
Customer: replied 7 months ago.
I can put it into gear, put my foot on the break, then put my foot on the gas while keeping the vehicle from moving using the brake, and I get the chirp. So the propshaft need not be in motion for the chirp to be present.
Expert:  Matt replied 7 months ago.
OK thats really starting to sound like a mountit would also be worth checking the differential mounts in the same manner as the transmission mounts
Customer: replied 7 months ago.
I discovered that the engine has to be at or above 2K rpms, too. Won't ever chirp below that, even under heavy load (in gear with foot on brake, accelerating).I'll attempt to check mounts again. Differential is 20' away (motor home) and chirp definitely in engine compartment.
Expert:  Matt replied 7 months ago.
hello ok another thing to check is the engine ancillaries, like the alternator or power steeringso if you pop off the serpentine belt again and turn each unit by hand feeling for tight spots or roughness
Customer: replied 7 months ago.
Agreed, but once again, wouldn't those things *always* chirp, not just when there's increased manifold pressure (decreased vacuum, retarded timing, etc.)?
Expert:  Matt replied 7 months ago.
hello ok if its definitely only under load I'd also check the state of the vacuum hose that runs to the brake booster as any leaks from the hose or within the booster will also 'squeal'