Engine will not start (2006 Chevy Express 3500 chassis)

[Ramblin__Rosie]

We have a 2007 Winnebago 331C Motor Home with a 2006 Chevy Express 3500 chassis (6.0 L V8 gas engine). We cannot get the engine to start. Here is a summary of what we have done, along with some hypotheses:


Problem

The starter cranks the engine with no problem, but it will not start. The engine will sputter briefly, but will not fire. We just got back home from a 1,400 mile round trip to Washington DC. The oil pressure light went on and off briefly a few times (it was on for a few minutes each time). Checked the oil a few times during the trip, it was full each time. The oil pressure gauge never went too high or too low.
Aside from the oil pressure light, we did not notice any problems during this trip. The first time we tried to start the engine after we got back home (the next day,) it would not start.

Things we’ve done

- Scanned for OBD codes several times with two scanners. No codes found.
- Inspected/cleaned the mass air flow sensor (did not replace it.)
- Replaced all spark plugs, wires, and ignition coils.
- Replaced the crankshaft position sensor.
- Checked fuel pressure at engine, 55psi (minimum limit, per the Haynes manual).
- Checked grounding wires/straps from the chassis to the engine.
- Looked for various fluid leaks. None found.

-------------------------------------------------
Possible Causes?

- Bad fuel?
- Clogged injectors?
- PCU problem?
- There is an “AUX START” switch on the driver’s side kick panel, below and to the left of the steering wheel. I damaged this switch when I removed the panel. This is a momentary switch which connects the motor home’s marine batteries to the vehicle’s electrical system, so the marine batteries can be used to start the engine, if the vehicle’s battery is dead. Is it possible that this switch needs to be assembled and in place to start the engine?

We welcome and and all advice! Thanks in advance!

[allbrandauto]

forgot to tell you. because you changed the crankshaft sensor it has to be calibrated to the truck. any auto repair shop should be able to do that for you will cost you a hour labor

[allbrandauto]

glad you got going next time don't pull fuses to look at them use a 12 volt test light

[Ramblin__Rosie]

allbrandauto wrote:
it takes spark fuel and compression to make a engine run. you said fuel pressure was good. start with spark is it good if no spark check all fuses.I have seen wire rub on the frame and blow the coil fuse.

Well, I just won the newbie mechanic of the year award.

After making arrangements to have the RV towed to my mechanic, I decided to check the fuses one more time, after reading your post. I noticed that the fuse for the Body Control Module (BCM) was missing. I also noticed that a fuse with the same amperage rating was in a slot that was designed "spare" (e.g. a slot should have been empty.) I moved the fuse from the spare slot to the BCM slot. The RV started without a hitch.

When I initially noticed that the engine would not start, I checked all the fuses, before I did anything else. I am sure I moved the BCM fuse to the incorrect slot when I did so. We then proceeded to replace the various components that are mentioned in my original post. The fuse was in the BCM slot when the problem surfaced, so clearly, one of the components we replaced was the culprit. However, whenever the original problem was fixed, the engine would not start, because BCM was not receiving any power. Long story short, we have no way of knowing what originally caused the problem.

Thank you to everyone who provided input!

[allbrandauto]

also this chevy has had ignition switch problems

[allbrandauto]

then you need a scanner to look at data

[PaulJ2]

Crankshaft position sensor controls the spark and engine timing. Cam position sensor controls the fuel injector timing. Have you checked/replaced that unit? Located where the distributor use to be, back of engine between the cylinder banks.

[Ramblin__Rosie]

We checked all of the fuses and relays that could be culprits. They are all fine. I checked each coil with a spark tester; spark is present on all 8 cylinders.

We have not done anything to check compression. That is beyond my level of expertise. However, I am not sure what could be causing a compression problem. The engine ran flawlessly for 1400 miles, then decided that it would not start.

allbrandauto wrote:
it takes spark fuel and compression to make a engine run. you said fuel pressure was good. start with spark is it good if no spark check all fuses.I have seen wire rub on the frame and blow the coil fuse.

[allbrandauto]

it takes spark fuel and compression to make a engine run. you said fuel pressure was good. start with spark is it good if no spark check all fuses.I have seen wire rub on the frame and blow the coil fuse.

[Ramblin__Rosie]

bguy wrote:
Did you bypass the switch?

Not a bad idea. however, I'm not sure how to do that. There are three wires that connect to the switch harness, but I am not sure what purpose each serves. I imagine they go to a relay somewhere.

The engine will sputter briefly when I try to start it, so I don't think the vehicle is completely immobilized for whatever reason.

[bguy]

Did you bypass the switch?

[Ramblin__Rosie]

That was the first thing we we tried, as a matter of fact. It did not seem to help with the problem.

MDKMDK wrote:
Will it start if you press the gas pedal to the floor while cranking? I had a similar problem on a 2002 5.7L Vortec. I think it was described in the owners manual. Think it cleared excess fuel from the cylinders from repeated crank no start.

From the 2002 Chevy Express owner's manual
"NOTICE:
Holding your key in START for longer than
15 seconds at a time will cause your battery to
be drained much sooner. And the excessive heat
can damage your starter motor. Wait about
15 seconds between each try to help avoid
draining your battery or damaging your starter.

2. If it doesn’t start within 10 seconds, push the
accelerator pedal all the way to the floor, while you
hold the ignition key in START. When the engine
starts, let go of the key and let up on the accelerator
pedal. Wait about 15 seconds between each try.

When starting your engine in very cold weather
(below 0
F or -18
C), do this:
1. With your foot off the accelerator pedal, turn the
ignition key to START and hold it there up to
15 seconds. When the engine starts, let go of the key.

2. If your engine still won’t start (or starts but then
stops), it could be flooded with too much gasoline.
Try pushing your accelerator pedal all the way to
the floor and holding it there as you hold the key in
START for about three seconds. When the engine
starts, let go of the key and accelerator. If the vehicle
starts briefly but then stops again, do the same
thing, but this time keep the pedal down for five or
six seconds. This clears the extra gasoline from
the engine."

[MDKMDK]

Will it start if you press the gas pedal to the floor while cranking? I had a similar problem on a 2002 5.7L Vortec. I think it was described in the owners manual. Think it cleared excess fuel from the cylinders from repeated crank no start.

From the 2002 Chevy Express owner's manual
"NOTICE:
Holding your key in START for longer than
15 seconds at a time will cause your battery to
be drained much sooner. And the excessive heat
can damage your starter motor. Wait about
15 seconds between each try to help avoid
draining your battery or damaging your starter.

2. If it doesn’t start within 10 seconds, push the
accelerator pedal all the way to the floor, while you
hold the ignition key in START. When the engine
starts, let go of the key and let up on the accelerator
pedal. Wait about 15 seconds between each try.

When starting your engine in very cold weather
(below 0
F or -18
C), do this:
1. With your foot off the accelerator pedal, turn the
ignition key to START and hold it there up to
15 seconds. When the engine starts, let go of the key.

2. If your engine still won’t start (or starts but then
stops), it could be flooded with too much gasoline.
Try pushing your accelerator pedal all the way to
the floor and holding it there as you hold the key in
START for about three seconds. When the engine
starts, let go of the key and accelerator. If the vehicle
starts briefly but then stops again, do the same
thing, but this time keep the pedal down for five or
six seconds. This clears the extra gasoline from
the engine."