Home » Public Forums » GMCnet » Fuel Delivery issue
| Fuel Delivery issue [message #321089] |
Tue, 25 July 2017 16:12  |
andyg
Messages: 12
Registered: January 2011
Location: Atlanta, GA
Karma: 0
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Junior Member |
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Posted this on Facebook, but want to see if there might be some insight here from folks that don't do FB
Hey GMC brain trust, The Pickle (1975 Palm Beach) is having a what I thought may be a fuel delivery issue. Little background, GMC has been set up as a food truck since 2004, and has been maintained as a working truck since. We are out working 3 to 5 days a week pretty much year round, in city/freeway traffic in the Atlanta area. Had the truck at the Coop in Jan for upgrades and to try to stay ahead of mechanical issues. New tranny, bottom of engine was rebuilt, fuel system was upgraded with new 12v pump on the aux tank, main is on the mechanical pump, rebuilt carb. . Also intake had cracks that were magnafluxed and and crossover plate installed to correct.
About a month ago on the way to an event on the freeway w/out traffic, truck just died, engine stopped getting gas, rpm when to zero. Since Jan had been running on just the main tank/using the mechanical fuel pump. Day wasn't that hot, mid 80s was cruising at 65/70 didn't seem like a vapor lock issue to me, check the engine compartment every seemed fine, would crank but not start. Switched to the aux tank with the 12v pump and it started up, got off the highway sitting in a parking lot at idle the engine was running hot 220ish so I shut it down.to let it cool off.. it was running ok, seemed a bit harder to start and had a bit of miss at idle, but didn't leave me stranded on the road. In the last couple weeks it has been running less well, losing power under load and up hills. I have replaced the mechanical fuel pump, and tank selector valve and the carb filter. Spoke to Jim B about it , he thought it might be the carb, so he sent a fresh one which we've swapped out as well.. Still not running right. Will start and run with aux tank/pump, no gas if set on main/mech pump.
Anybody have any insight, ideas or suggestions. I am leaning toward it being two problems. The issue with the mechanical pump/ and the poor performance. I did get a vacuum gauge on the engine yesterday, 15 or so at ideal, between 10 and 15 in gear and below 10 under load. Jim is thinking there is some sort of vacuum leak. Any ideas are appreciated. Thanks!
Andy Grimes
Atlanta, GA
"The Pickle" 1975 GMC Palm Beach
ultimateculinary.com
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| Re: Fuel Delivery issue [message #321095 is a reply to message #321089] |
Tue, 25 July 2017 17:52  |
lqqkatjon
Messages: 2324
Registered: October 2010
Location: St. Cloud, MN
Karma: 5
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Senior Member |
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I want to add from what I understood he did go get a boat gas tank and tried to run it by connecting direct to fuel pump. Told me there was no fuel from fuel pump and engine would not start trying to use boat gas tank. Pump is new.
Jon Roche
75 palm beach
EBL EFI, manny headers, Micro Level, rebuilt most of coach now.
St. Cloud, MN
http://lqqkatjon.blogspot.com/
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| Re: Fuel Delivery issue [message #321096 is a reply to message #321095] |
Tue, 25 July 2017 17:59 |
Justin Brady
Messages: 769
Registered: April 2015
Location: Bell Buckle, TN
Karma: 11
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Senior Member |
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Sounds like the fuel pump. I know you replaced it but that doesn't mean it's good. Chinese parts these days...
Get a block off plate and a Carter electric pump mounted to the frame and be done with the mechanical all together.
Justin Brady
http://www.thegmcrv.com/
1976 Palm Beach 455
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| Re: Fuel Delivery issue [message #321142 is a reply to message #321096] |
Wed, 26 July 2017 10:51 |
andyg
Messages: 12
Registered: January 2011
Location: Atlanta, GA
Karma: 0
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Junior Member |
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It could be the new pump, but the way the original pump stopped working and the new one doing the exact same thing makes me think it's something else.
We have been considering going to a second electric pump. Is there a preferred configuration for the second pump? The pump on the Aux pump is between the tank and the selector valve.
My goal is to get the system as dependable as possible. As it is now the truck is starting normally on the electric pump but not running well under load. I suppose we could just bypass the pump as it's set up now and just run the Aux tank and see if that improves the performance. Is there any downside in this idea?
As for dependability, what are folks thoughts on fuel injection vs the carb system. Don't mind spending the money if it takes some worry/stress out of my life. Would FI make more sense then just going to a two pump system with the carb?
Andy Grimes
Atlanta, GA
"The Pickle" 1975 GMC Palm Beach
ultimateculinary.com
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| Re: Fuel Delivery issue [message #321143 is a reply to message #321142] |
Wed, 26 July 2017 11:04 |
lqqkatjon
Messages: 2324
Registered: October 2010
Location: St. Cloud, MN
Karma: 5
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They all have pro's and con's
As for fuel pump installation you want pumps as close to tanks as practical. Electric Fuel pumps can fail, so running an electric on each tank you should always have a 2nd pump/tank to fall back on.
Most people go to 2 electric fuel pumps to solve vapor lock problems. The mechanical pump is usually the more reliable pump other then vapor lock issues.
Wiring in multiple pumps takes a little thought as far as relays and wiring and such. Making sure pumps
Do not run when they should not.
As far as fuel injection, there are lots of options and some performance improvements, But you are also introducing failure points. So can be a trade off.
Fuel injection will not fix the problems you are having now. Something or multiple things are going wrong.
You are located in atlanta, it would be good to have a second set of experienced eyes looking over the problem. You dont want to spend money on fuel injection if something is majorly wrong with engine.
Jon Roche
75 palm beach
EBL EFI, manny headers, Micro Level, rebuilt most of coach now.
St. Cloud, MN
http://lqqkatjon.blogspot.com/
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| Re: Fuel Delivery issue [message #321145 is a reply to message #321089] |
Wed, 26 July 2017 11:46 |
lw8000
Messages: 201
Registered: July 2012
Location: S.E. Michigan
Karma: 1
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Senior Member |
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It sounds very much like vapor lock to me, we've had it when it reaches about 85 degrees or more on a consistent basis. We too have the exact same setup with the aux electric pump (installed by JimB as well), and it works every time to correct the issue long enough to switch back to the regular tank. I've been slowly doing some additional things to the coach to try and cool down the engine box little by little to see if we can prolong the time it takes for the vapor lock to start. I figured I would post everything at once, when I have some sort of results.
Chris S. -
77 Kingsley, 3.70 FD, mostly OEM -
S.E. Michigan
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| Re: Fuel Delivery issue [message #321148 is a reply to message #321089] |
Wed, 26 July 2017 11:59 |
andyg
Messages: 12
Registered: January 2011
Location: Atlanta, GA
Karma: 0
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Junior Member |
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Thanks Jon. Good points. Been talking through the issues with JimB, who did the work in Jan. He's been helpful, but difficult to really do effective trouble shooting over the phone. Have a mechanic here who is capable, but by no means a GMC expert. Is there a mechanic other then Zeb at Southland that people have used in the Atlanta area with good results on their GMC?
Andy Grimes
Atlanta, GA
"The Pickle" 1975 GMC Palm Beach
ultimateculinary.com
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| Re: Fuel Delivery issue [message #321151 is a reply to message #321148] |
Wed, 26 July 2017 12:18 |
77Royale
Messages: 461
Registered: June 2014
Location: Mid Michigan
Karma: 6
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Senior Member |
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For 20 bucks and 30 minutes of time, I'd put in another new Carter 6108 mechanical pump and run the boat tank to see if that makes any difference. You didnt say if the fuel lines were all replaced recently. Possible one is gummed up if its old, one of the in line filters other than the carb filter is clogged, or hoses which are cracked/damaged/pinched.
Another new mechanical pump and the known good boat gas can will rule out all that other stuff (selectors, elect pumps, relays, wiring several yards of fuel line) back toward the tanks at a minimum.
Then if that runs well, start eliminating things one at a time working back.
Id also take a good smell of the oil and check the engine oil level to make sure one of the mechanical pumps didnt puke fuel into the crank case. oil that stinks like raw fuel is no good.
77 Royale, Rear Dry Bath. 403, 3.55 Final Drive, Lenzi goodies, Patterson carb and dizzy.
Mid Michigan
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| Re: Fuel Delivery issue [message #321375 is a reply to message #321089] |
Mon, 31 July 2017 07:33 |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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Senior Member |
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After vapor locking on I 75-85 at the Brady curve one Monday afternoon at 5P I heal;ed my problems pretty much permanently with this setup:
http://www.gmcmhphotos.com/photos/g6198-cane-9-creek-rv-park-heflin-2c-al.html
A pair of Mr Gasket electrical pumps and a relay to switch. They have built in backflow valves. Discard the sup[plied filters and buy a pair of the Wix exact replacements, the originals will looseb at the swaged fitting and leak. Blankflange the mechanical pump-. I'm off the rest of the week to VA, but back nect week, PM me of you have questions.
johnny
Braselton
Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
I forgive them all, save those who hurt the dogs. They must answer to me in hell
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