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Matt, Engineer
Category: RV
Satisfied Customers: 20391
Experience:  Honors degree in Mechanical Engineering, worked 8 years as a Formula 1 engine engineer.
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HOT start problem with 2002 Workhorse V8 in my motorhome.

Customer Question

HOT start problem with 2002 Workhorse V8 in my motorhome. Engine runs fine until I stop then it will not start again until I let it cool down for 15 to 30 minutes. It has been suggested that I might have a fuel pump vapor lock but that does not seem logical since the fuel pump is in the tank (or at least I think it is). Also have had suggested crankshaft sensor but that does not really make sense since the problem exits only on re-start. Any ideas? I am on the road now in Utah and dealers are not nearby.
Submitted: 3 months ago.
Category: RV
Expert:  Matt replied 3 months ago.


This could be a wiring issue as things tend to expand when hot and its possible a poor or partial electrical connection is being pushed apart on one of the major sensors so check the connection plug and wiring to the following;

Airflow meter

Crank position sensor

Cam position sensor

O2 sensor

Throttle position sensor

unplug each in turn and use some switch / contact cleaner spray on the pins to ensure its all grease / dirt free

Also worth checking the connections to the fuel pump for the same reason - unplug each in turn and give them a good squirt of switch / contact cleaner - Not WD40

and also unplug and inspect the main power relays and fuses for signs of overheating or corroded terminals - so the ones for the ECU and the fuel pump

And also unplug the wiring loom connections in the engine bay one at time and inspect for corroded or recessed pins.

Check the resistance of the spark plug leads ( 13-15Kohm / metre) and replace if any doubt or high resistance - Also replace the spark plugs if any of them fail this checklist:

Also its worth checking that the electric pump that feeds the injectors is working correctly, it should run for a few seconds then switch off when you first turn the ignition on. If the connections to this are corroded or damaged then the pump could stop at any time. Check that its relay switches in and out and the relay contacts are clean and bright – replace the relay if in any doubt and do the same for the fuse, ideally measure the voltage at the pump and check its getting 12V

Also check for exhaust leaks before the o2 sensor as if this has been experiencing an exhaust leak then it will have been running very rich as the sensor will see the extra air pulled in as fresh / lean fuelling and be adding fuel to compensate.

this can lead to catalyst failure as the extra fuel can re-light inside and melt the catalyst

The best way to find an exhaust leak is to run the engine from cold and feel around the exhaust joints with your bare hands - you'll have about 30 seconds before it all gets too hot and you should feel any escaping gas blowing over your fingers

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