454 Engine Problem

[85/345]

Got everything fixed with the batteries, now I have a problem with the engine. The engine will run fine until it is warmed up and than it will just quit and I will not be able to restart it. I will let it sit for 5 or so minutes and than it will crank right up and go again. Anyone got any ideas on what it could be.

Brian

[87MH]

Easy enough to diagnose -

Start engine with the air filter off. As soon as it stops, look down into the carb and activate the throttle (take the key out of the ignition first) and observe whether or not there is fuel present, if not, start checking fuel filters, electric pump, and lines - lots of info here in previous threads about fuel delivery in the 345's.

If fuel is not the problem, check for spark during the "no start" period.
If electrical problem is determined, I would start with the coil (most likely culprit), and diagnose both "upstream" and "downstrean" from there.

[swebster]

I agree with Dennis. Sounds like fuel delivery to me but certainly check the spark as well. also check to make sure your choke is opening up all the way.

[overlander63]

GM ignition modules have been a problem, if it turns out to be that, it is inside the distributor, under the rotor. Should be two 3/16" head screws holding it in. Be sure and use dielectric grease under the new module, or it will fail in short order.

Terry

[MikeL]

It takes 4 things to make an engine run---fuel---ignition<spark>---compression--and timing. All you have to do is determine which one is missing when it refuses to start. While there are things that can cause compression and timing to come and go it's highly unlikely. Dollars to donuts it's fuel or ignition. An easy way to check ignition is to pull a plug wire off , attach an known good spark plug to it and lay it on the engine. While someone cranks the engine check for spark at the plug. Caution,,,watch where you put your hands, sleeves, etc while you do this . It's easy to get wraped up in a fan belt when your in the engine compartment.-----Pieman

[59toaster]

Choke is not opening.

Quick way to verify is watch the choke after you start the engine It should be fully open within about 3-4 minutes. if it doesn't open if will drowned the engine.

Verify power to the choke element once you start it cold. Round doohickey on curb side of carb with one plug). The engine has to be running for it to get power. There is a oil pressure switch that will not send power to the choke if there is no oil pressure. On a 350 that switch is behind the distributor. I think on the 454 its above the oil filter on the side of the block or its on the street side of the block just in front of the motor mount. The sensor will have 2 or 3 wires on it depending on the carb. There is a Quad that has a fuel mis solenoid and it will have a wire for that.

If there is power then meter the resistance on the element. I think its suppose to be 45ohms but its been a while since I have checked one.

[85/345]

Finally got around to analyzing everything that deals with the fuel system and it ended up being the electrical fuel pump. To figure this out I put a clear filter up next to the carb and drove the AS around town. When under load the filter would go empty. So that's when I figured that it had to be the fuel pump. Changed the fuel pump and drove it on a 60 mile trip and no problems.

Thanks for all the help.
Brian

[ALANSD]

great job of self diagnosis. Common failure for sure on your model.
The other item mentioned- the ignition module, is a spare part that is worth carrying also. Inexpensive insurance.

[donnall]

Sounds like a classic example of a bad coil to me.

Coil cool it runs, coil gets hot it quits.

At least that's the first place I look.

Don

[swebster]

Brian - nice job! Good idea to use a clear filter up front to "see" what was going on with fuel pressure. Another "shade tree" diagnostics device I'll remember for the future.

[85/345]

I changed a lot before I figured out it was the fuel pump. I just left the new parts on and will keep the old ones for spares. From what I have learned from this forum is that you can never have too many spare parts for these beauties.

Thanks,
Brian

[ALANSD]

true- somewhere in the archive folks posted lists of what they were carrying with them on the road...quite amazing

(edit) actually here is the thread I mentioned----

http://www.airforums.com/forum...ht=spare+parts

[RichardT]

Does your motorhome look like this?

Hi Brian this is Richard in Bat Cave.

[85/345]

That would be my lovely lady!

[swebster]

nice looking 345. but to me every 345 is a work of art

[Auretrvr]

I'm thanking our lucky stars this happened at home and not while we were on the road!

We just got back from a 2,000 mile trip in our '83 310 (Ernestine). I filled her with gas and parked for a couple of days after we got back.

This morning I started it to warm up for a trip to the shop, and she died after about 10 minutes.

I'm a little spooked by this because I just put a bottle of Sta-Bil in the gas tank the other day. But my Onan Generator is running just fine on the same gas as the chassis engine.

The 454 starts, runs maybe 5 minutes and stops. After it sits for a bit I can start it again but it again stalls out. Once it has warmed up, it only runs for a very short time -- 10-15 seconds -- before it quits.

I connected a hose to the fuel line at the carburetor and watched it rapidly pump gas into a bottle. When it stalls I can pump the accelerator and see it shoot gas into the carb but it doesn't affect the stall.

I did check for spark but maybe I waited too long after it stalled, because it had spark when I checked it. I will redo that test.

I followed a mechanic's advice and replaced the manual fuel pump. No change.

Does the electric fuel pump normaly run slower once it has built up pressure? Mine never slows down. This could mean a bad pump or leaking tank line, right?

Would a bad coil suddenly start failing when warm? Would it be a very consistent failure, as though it were just shutting off at a certain temperature every time?

Seems like a case of having gas and spark but maybe not enough or not all the time!

Thanks!

[59toaster]

Originally Posted by Auretrvr

I'm thanking our lucky stars this happened at home and not while we were on the road!

We just got back from a 2,000 mile trip in our '83 310 (Ernestine). I filled her with gas and parked for a couple of days after we got back.

This morning I started it to warm up for a trip to the shop, and she died after about 10 minutes.

I'm a little spooked by this because I just put a bottle of Sta-Bil in the gas tank the other day. But my Onan Generator is running just fine on the same gas as the chassis engine.

The 454 starts, runs maybe 5 minutes and stops. After it sits for a bit I can start it again but it again stalls out. Once it has warmed up, it only runs for a very short time -- 10-15 seconds -- before it quits.

I connected a hose to the fuel line at the carburetor and watched it rapidly pump gas into a bottle. When it stalls I can pump the accelerator and see it shoot gas into the carb but it doesn't affect the stall.

I did check for spark but maybe I waited too long after it stalled, because it had spark when I checked it. I will redo that test.

I followed a mechanic's advice and replaced the manual fuel pump. No change.

Does the electric fuel pump normally run slower once it has built up pressure? Mine never slows down. This could mean a bad pump or leaking tank line, right?

Would a bad coil suddenly start failing when warm? Would it be a very consistent failure, as though it were just shutting off at a certain temperature every time?

Seems like a case of having gas and spark but maybe not enough or not all the time!

Thanks!

It's the Choke.
It's not opening.
GM wires the choke through a oil pressure switch so that the choke only gets power when the engine is actually running. This is to prevent a hard start if you turn the key to run and don't actually start the motor.

When it is cold start the motor with the air cleaner off. Hook a Volt meter to the choke wire and verify that when it starts it gets 12v once it starts and has oil pressure. If it gets 12v then the element has failed. If it doesn't get power trace it back to the oil pressure switch and check for power there. No power start looking for blown fuses.

On a 350 the switch is in a oil port right behind the distributor. My 454 is Fuel injected so not sure it where they put the switch. It may be down on the driver side of the block right above the oil pan up near the front of the motor. That's where the fuel pump switch and sender for the gage is.

You should also see the choke open as the motor warms from cold when the choke is plugged in.

[Auretrvr]

This was a lesson in troubleshooting discipline.

I did check for spark, but not until after the module had cooled down some--so it was working again. This morning I tested immediately after the engine stopped and there was NO spark.

$20 at Advance Auto Parts and I'm on the road again!

Lesson learned: The way I described my problem to the mechanic led him to suspect fuel problems ahead of electrical.

The GM HEI ignition apparently had a reputation for this type of problem but today's mechanics don't see that much of 25 year old motor homes!