Engine stubbles at idle speed

[Gjac]

The MH in my signature has become Ihard to start and falls flat when I give it the gas. The problem seams to be progressing. Changed fuel filter before trip, ran can of seaform. Still does it when it's hot. Runs normal once im driving.

[wildmanbaker]

Yes they did Bud, and they had a Directory for the Standbys'. When people have trouble on the road, they sometimes go into a kind of shock, and have trouble reasoning things out. It just helps to have someone to talk things over with. I though the idea was a good one.

[enblethen]

I too am at a loss!
I would like to add that when Good Sam was in early times, there was a group called Standby Sams that was there to help others having problems on the road. This list showed their locations.
It is a shame that more of us here do not offer to help!

[wildmanbaker]

Bud,
Great job! It is strange that under heavy loads it would run good. Just the opposite of what you would expect.

[enblethen]

Gary is on the road as I type headed for Yakima River canyon south of Ellensburg, WA.
Rig sounds good!

[azrving]

Heck yeah, great to hear that. I know when electric pumps are used in cars etc that running them real low on fuel/fuel slosh can shorten their life. My daughter texted me a pic of the high outdoor temps on her dash display on a 2015 Mazda. When I texted her back and said I thought I told you to not run cars low on fuel! She texted back that she reaized as soon as she had sent the text she knew that I was going to rag on her about that. Aint gettin nuttin past the oldman. 🙂

Safe travels to you.

[Gjac]

Just got a call from the shop they test drove it and it works. It was an expensive lesson, the cost to diagnose and replace fuel pump was $ 1100 plus all the parts I changed trying to fix problem. The previous owner changed the pump before I bought it. If your MH fails to start with one crank and you need to give it gas to start it spray some starting fluid into tbi and see if it stays running. Thankful that it is now fixed and thankful to Bud for all his help he took us to Grand Coolee Dam and saw the lazer light show and Leavenworth which is a reconstruction of a Bavarian village while we waited for the MH to be fixed, stuff we would never have found on our own. So now on to Mt Rainer. Thanks again to all who posted ideas.

[wrgrs50s]

Keep us posted ! Sure has been a mystery ride. I have a brother with a 1987 Aluma Lite with the carbeurated 454. He had similar issues and I got him a distributor complete at Amazon, changed plugs and wires to rule out electrical and these were due anyway from age. That resolved his problem after lots of failed troubleshooting. That's why I previously suspected a distributor related issue with yours.

Hoping the fuel pump does the trick for yours. These things can sure be a booger to figure out sometime.

[enblethen]

It would be good if it wants to fail when they are doing test drive, not when you are ten miles down the road!

[Gjac]

What was strange about this problem was when the psi tested good and the injecters had a nice cone and it ran well at hight speed it sounded more like an electrical problem rather than a fuel problem. One would think there would be greater demand for fuel at high speed rather than idle, never heard about checking fuel volume either but when I saw that young mechcanic spray that starting fluid into the tbi and it stayed running I wished I thought about that a week ago. Even the older mechanic was still not convinced. They installed the new pump while the tank was down and it was still up on the lift and it started by just turning the key.They should finish it by noon and test drive it . I trust it won't die when they put it in drive.

[azrving]

Gjac wrote:
Was not the timing 150 psi on both sides. The older expierenced mechwas baffled. One of the young kids he trained took starter fluid and sprayed it into the carb and it ran. He said just because it had 15 psi it may not have the volume. Order a new fuel pump will get MH back tomorrow. Hopefully that fixes it .

It's fuel related. I dont think I've ever seen a volume/time spec but it should fill a pop bottle pretty quickly when free flowing. Yes, pressure and volume are two different things. Also seen connectors, corroded wires not provide proper voltage. Anyway you will have it straightened out soon. Hang in there.

[Gjac]

Was not the timing 150 psi on both sides. The older expierenced mechwas baffled. One of the young kids he trained took starter fluid and sprayed it into the carb and it ran. He said just because it had 15 psi it may not have the volume. Order a new fuel pump will get MH back tomorrow. Hopefully that fixes it .

[wildmanbaker]

Al most all manufactures used nylon gear on the cam gear for quiet operation. Heavier duty engines had the steel, but the chain doesn't like operation above 3,000 rpm for extended operations, and them wears the gears. This was a common failure. I always recommended changing the timing set on GMs at about 70,000 miles. A lot cheaper than what happens if it fails.

[Gjac]

wildmanbaker wrote:
You should not see more than 300 ohms on any wires. Lightly pull and twist the wires as testing them, as their may be bad areas on the inside. Bad wires usually do not show up at idle, as it only takes about 5,000 volts to fire the plugs. As loads increase, it will take more voltage to jump the gap, and that is when bad wires show up. Has anyone put a timing light on it? IS the timing jumping back and forth more than 5 degrees? Check slop in the timing chain by turning the engine forward until you see the rotor start to move, then turn the engine backwards until you see the rotor move the other direction. If it takes more than 10 Degrees of movement at the crank pulley, it may be the timing chain has jumped a tooth. Keep plugging, and let us know what turns up.

. Talked to the mechanic at the shop he checked all the sensors and found no problems. He was thinking that it was a timing issue also. He was going to do a compression test tomorrow morning to see. He said that vintage had nylon gears and the gear could have worn gradually. He said that they usually go bad at 80k miles or so I have 113k now. If it jumped a tooth it would have happen all of a sudden. Sounds logical to me but so did all of the other suggestions. I was surprised to learn Chevy used nylon gears I thought they were steel. I gave him your idea also to check for the 10 degree movement.

[azrving]

Good to hear that. Hopefully they get it straightened out for you.

[enblethen]

It is at a shop. They are doing compression test as soon as engine cools down.
Replaced the plug wires this morning with no change.