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Powertrain Q & A: Feb 2003

Originally Published in MotorHome Magazine

Q.   We have owned a new Trail-Lite Class A motorhome by R-Vision
for three months. We have taken it on four trips and on three of those
trips, it has stranded me. After running fine for hours at a time, the
engine quits if I stop or slow down. The first time, I was in a busy
intersection in the Mojave desert. It took me 35 minutes to get it to
start. Needless to say, it was a bit scary being with my family in the
middle of the intersection while semis tried to get around us.
On the second trip, the engine stalled at the top of the Baker grade in
California. I was going 60 mph down the grade, towing a boat, without
power-assisted steering or brakes. I tried putting the engine in neutral
and starting it, but no luck. I got the coach to the side of the road,
and it started in five minutes.

On the third trip, the engine stalled as I slowed down at an
agricultural-inspection station. I blocked one lane for 10 minutes
before I could start the engine again.

It’s been serviced at a dealer after each breakdown. The mechanics
flushed the fuel injectors and reprogrammed the computer after the first
breakdown. They installed a new fuel pump after the second breakdown. I
called the factory and the technical person I spoke with thinks the
problem is electrical. The dealer can’t duplicate the problem. I have
put 1,500 miles on this motorhome and can’t continue to take the risk of
driving it with my family.

Please help if you can.

–Mike Morley, Via the Internet

A.   Saying that the problem is electrical is like saying
that the Titanic’s problem had something to do with water. It’s not
wrong, but it’s not very helpful in figuring out what went awry.

The problem is a loss of fuel delivery or a loss of ignition spark.
Your motorhome’s problems seem to be similar to the intermittent
fuel-pump failures that are fairly common; they occur most often when
the engine is hot, and then it begins working after a cool-down period.
However, many electrical components will act similarly and begin working
after they cool.

I would do some testing to determine whether the stalling and
hard-starting is caused by lack of fuel or spark. If the problem always
happens on hot days, you may be able to duplicate the condition at a
shop with a chassis dynamometer, where you could run it under a full
load without a lot of airflow. This will also be much safer than on the
road, in case it stalls. Have the shop mechanics connect a fuel-pressure
gauge and an automotive-type oscilloscope to the ignition during
testing. That way, they can trace the problem when it appears.

Q.   I am a longtime reader and fan of your column, and I
have a problem that I don’t recall ever seeing discussed in it. We have a
35-foot 1995 Pace Arrow motorhome with only 25,000 miles on it. I have
had to replace the main solenoid twice already. It’s the one that just
about everything goes through, including the starting motor, the leveler
jacks, the window fans, the driver’s window and likely a few more
things that I haven’t discovered yet. This is not the switch that I
would disconnect when I park for the winter (battery disconnect), but
rather it is the one that automatically activates when I turn the
ignition switch on and allows current to flow from the alternator to
charge the coach battery. (At least that is how the dealer described

This last time the solenoid got so hot while I was driving that I
could smell it and the outer case warped, but it would still work if I
turned the ignition key on and off enough times. After replacing the
second one, I tried to get the dealer to determine the cause of the
failures. My dealer contacted the Pace Arrow factory and was advised
that the continuous-duty solenoid it had installed was the same one
installed on all its motorhomes and the company had not experienced any
problems with it. My dealer also claimed that the replacement solenoids
he had installed were the same as the factory-installed one and that he
hadn’t experienced any problems with them, either. He suggested that the
only possible problem would be a faulty voltage regulator that would
allow too much voltage to the solenoid, which would fry it.

The voltage was checked, and after running for an hour at both idle
and high rpm, the voltage was absolutely steady and never exceeded
13.8, which I was told was well below the maximum. The dealer said that
if the solenoid kept failing, he could install an isolator to replace
it, but said there wasn’t room for it in the electrical compartment, so
it would require extensive rewiring.

This didn’t make a lot of sense to me, so I checked with an
automotive supplier, and he had a heavy-duty solenoid used in farm
tractors and big trucks that he thought might be the answer.

Can you suggest any other tests that might determine the cause of
the failures? I think the solenoid is merely the weak link in the chain.
I really would like to determine why it continues to fail and fix the
root of the problem.

–George Bardsley, Minnedosa, Manitoba

A.   You mentioned that starter current goes through this
isolation relay. Normally, starter current does not pass through the
charging isolation relay. I suspect that the relay is miswired. Check
this first.

The 13.8-volt reading is normal. If the charging rate was high
enough to fry the relay, the alternator should have quit by now, or the
batteries would be boiling over. I recommend you use an inductive
ammeter (such as a Sun brand VAT tester) to measure how much current is
going through the relay during all operating modes, and make sure it’s
within specifications.

Then make sure that the relay is indeed the correct continuous-
duty unit, and not a Ford type starter relay that got slipped in by
mistake. Sometimes products get boxed up and/or labeled wrong, even from
the factory. If the current that the relay is handling is normal, it
wouldn’t hurt to use a relay designed for heavy equipment.

Q.   We have a 1989 Class A motorhome on a GM P chassis, and
I am looking for information on the in tank electric fuel pump. I had a
problem with the motorhome acting like it was fuel-starved, but the
filters are OK, and I changed out the oil pressure switch and the
fuel-pump relay to eliminate the possibility of an intermittent
electrical fault. I tested my pump and it is pumping 4.5 psi, controlled
by a Holley fuel pressure regulator, and I measured 36 gallons per-hour

Fleetwood told me to contact Chevrolet, but the company didn’t
help. I am at a loss after checking with dealers and repair shops. Can
you help me? The motorhome has a 90- gallon tank, and to change out the
pump is a real pain. Is it possible to install an external electric fuel
pump and draw through the internal pump?

–Jim McNally, Via the Internet

A.   The fuel system has a return line that connects at the
mechanical pump. If this bypass is not working properly, or the
regulator is faulty or set incorrectly, pump output will return to the
tank and not enough fuel will get to the carburetor.

To flow-and pressure-test, it is necessary to measure the fuel
pressure at the inlet to the carburetor. There should be 4-to-5 psi of
fuel pressure at the carburetor at idle, with a minimum of 2-to3 psi
under full load. Check volume after you have verified that the pressure
is correct. The factory recommends a minimum of 25 gallons per hour at 2
psi and 3 psi maximum at full throttle and load. That’s not easy to
measure, but if it puts out about a pint a minute at idle it should be
fine, assuming the pressure is within specs at full load.

I don’t recommend adding an external pump. The dead pump in the
tank becomes another restriction, and the intake side of pumps is very
sensitive to restrictions. Besides, the extra plumbing and wiring can be
a fire hazard.

Q.   This is in reply to Brian Thomson’s inquiry in the
September 2002 Powertrain Q&A about his 1979 Class C with a Dodge
chassis running hot. I had a similar problem with a 1987 Ford Class C
equipped with a 460 engine. In 1998, I put the motorhome in storage, and
in the spring the engine ran hot, similar to Brian’s Dodge. I changed
the radiator, the coolant pump, the timing gear and chain, the fan
clutch, hoses, belts, the thermostat and dual exhausts, to no avail.

Somehow I encountered information on the “green” ethyleneglycol
antifreeze. If the antifreeze is older than 18 months, it may jell in
some parts of the engine. I flushed the engine several times with clean
water, and each time helped. There was no evidence of foreign material
in the flush water (dirt, rust, etc.). The engine ran a little cooler
with each flush.

Also, the makers of the orange antifreeze, Dex-Cool, have told me
that Dex-Cool will help remove the jell and has an indefinite shelf
life. I have changed the Dex-Cool antifreeze once each year for the
past three years, and my engine is finally back to a normal temperature
in all driving situations. Perhaps you can pass this on to Brian.

–R. Patrick, Catlettsburg, Kentucky

A.   Thanks for the note. Apparently there are still a lot
of Dodge motorhome chassis out there, judging from the number of
responses we got.

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