suburban tow truck fuel issue
 

all right im tossing in the towel and begging someone smarter than i to assist with a 6 year old issue of losing fuel pressure ...

1990 suburban 1984 454 .040 reasonably fresh (has been out twice during this issue) , aluminum intake, RV cam, headers and a Qjet.
original tank mounted efi pump replaced with 3/8 copper line to bottom of tank
now have holley high perf mechanical pump
now have added carter in line small electric pump
fuel line is new from bottom of tank to carb, routed away from heat & insulated under hood
gas cap has hole drilled in it

has 7-8 lbs pressure when started ...
however after 1 hour or so of towing im running out of fuel at 2500rpm
if i stop i have 1-3lbs of pressure (guage inline under hood)
fuller tank seems to help but not 100%
temp of truck seems not to be an issue NEVER gets over 210 mostly 180

been 6 years, tanks been out 3 times, ran fuel line twice, two stock mechanical pumps plus holley and electric booster... im ready to put on areomotive 500gph and regulator or sell this thing while SCRAP is high !

help,
captain jack

Re: suburban tow truck fuel issue
 

These trucks had a problem when they first came out with the baffle in the bottom of the tank coming loose. Back then they would come loose and move around and knock the electric fuel pump loose causing the truck to die and be towed in. I fixed hundreds of them back then at the dealer I worked at. I dont know your setup but maybe yours is loose and causing a problem with your pickup in the tank. I still see one every couple of years. If yours is loose the choices are new tank or find someone with very small arms to go in a put new sheet metal nuts on to hold it back in place.

Re: suburban tow truck fuel issue
 

Did you install a sock type filter on the end of the fuel line in the tank?

My 1996 GMC started having stalling issues and after going round and round it was fine silt in the sock filter.....it would collapse and lose fuel pressure. This was a Vortec SFI engine and ran with 50 lbs fuel pressure.

I was on the hook once and had trouble numerous times before I saw what the issue was.

I attributed it to buying gas from some el cheapo stations. The fuel tanker truck might have been there when I got fuel.......stirs up the crap on the bottom of the tank and the cheap sob's never change their filters at the pumps......I found a reddish very fine silt in the sock.....

Re: suburban tow truck fuel issue
 

rob ive removed the pickup and replaced the entire tube to the bottom of tank, wrapped it in screen... did not see (could i see it??) or hear anything loose ?

thanks
jack

Re: suburban tow truck fuel issue
 

Jack just wondering if your problem is possibly a fuel tank that originally was non vented and now with the pump you are running it may require it to be a vented style?

Re: suburban tow truck fuel issue
 

If you pull the sending unit out and look in there its a big piece of white plastic. If there is fuel in the tank it will float a bit and if you slosh the fuel around you will hear the baffle hitting the sides of the tank. If your arms are small you can stick it in the hole and grab ahold of it. If it moves at all its moving too much. I used to be able to get my arm in far enough to put the baffle back over the studs made on the metal tank and start the nuts then I used a long 1/4 extension with a swivel socket on the end to tighten them up. It was a very common problem back then. My thought was that maybe it was floating up and blocking the inlet of your pick up tube.

Re: suburban tow truck fuel issue
 

I'll take a stab at this because I had a similar thing happen to me once.

Did you happen to route the new fuel line right next to the transmission cooling lines by any chance? In my case, the car always ran great on the first pass then once the trans was hot, it wouldn't run hardly at all. Re routed the fuel line and the problem went away.

Re: suburban tow truck fuel issue
 

I built a 391 Ford for one of my dads box trucks years ago. He calls me about a week later telling me it would die intermittently. If you let it sit for a minute it would restart and run fine, until it died again.

Replaced the fuel filter, fuel pump, carb, replaced the fuel lines, even the distributor.

Finally dumped and cleaned the tank, about twenty little tin foil disk from the top of gas additive bottles came out. They would float around for awhile then get sucked over the intake hole.

Have you cleaned the tank throughly?

Re: suburban tow truck fuel issue
 

tank has been off 3 times never notice any dirt, or anything else in it. sock is gone just tube with screen over it with hose clamp holding it on. cap has been drilled to vent. lines are now routed outside frame rail up over inner fender and insulated everywhere under hood...

was wondering about drilling hole in bottom of tank for pickup like a fuel cell... oem always had top exit for safety ??

thanks, keep coming with ideas !

Re: suburban tow truck fuel issue
 

Sounds like a condition caused by heat is percolating the gas,either in the line or engine compartment.Checked condition of fuel filter?
You can try refridge line sleeves near hot areas in fuel lines are.
Just some guesses from a two left handed psuedo mechanic.

Re: suburban tow truck fuel issue
 

I have repaired that type of problem many times. The frame is getting hot enough to boil the fuel. If you do not have a return line you need one. If you have a return line then insulate the fuel lines or move the to the outside of the frame to get away from the exaust. Here in south Texas i have done this type of mod with good results.

Re: suburban tow truck fuel issue
 

The inner fender is the wrong place to route fuel lines. Chevrolet put them on top of the frame rail on cabureted trucks because air flows there.

The big block carbureted trucks had a 1/2 fuel line from the tank all the way to the fuel pump, it was necked down for a 3/8" hose. They also had a different pick up in the tank. I always used a genuine Delco fuel pump for a 70 Chevelle on my big block trucks, that seemed to be the most reliable and effective mechanical pump, the big Holley race style pumps would at times have pressure spikes that caused a Q-Jet to flood.

See if you can find the correct fuel tank and the correct sending unit and pick up for an earlier truck with a big block and a carburetor. You can probably even find the fuel lines.

Re: suburban tow truck fuel issue
 

Oops. Sorry, I missed part of the original message.

Re: suburban tow truck fuel issue
 

?? Alan, I put 386K miles on an 86 454 GMC Suburban (last carburated model), but it had a 3/8 line. The line did run outside the frame rail mounted toward the top of the frame channel, if that is what you mean by the top of the frame. I replaced the fuel pump once and used a NAPA pump. No problems ever. I replaced the tank once (the original developed a split along the bottom) with a tank from an 89 model. I used my pickup and sending unit, still no problems. 40 gal tank.

Jack, that's weird!!

Re: suburban tow truck fuel issue
 

Dwight, most of the 454 trucks (3/4 ton and up) we had in the shop, Suburbans included, had 1/2" lines. Not all did though, you're right. Yes, the fuel lines do run outside the frame, high on the side and on the top in places. They were out there to keep them cool, and keep them away from shrapnel from failed drive shafts and such.

Now that you mention in though, around here, most every C/K 20 series truck was a "C6P" truck, which had a heaver GVWR. The dealers just ordered them that way. But you could get the C/K 20 series without that option, and those did not have all the heavy duty equipment. A "C6P" truck was just about a 1 ton truck. I'm pretty sure that the few trucks we had through the shop that did not have those lines were not "C6P" trucks, that would explain it.

Re: suburban tow truck fuel issue
 

If you have (after market), rear A/C, make sure they didn't tie the A/C lines to the fuel line as they will cause vapor lock. On my '85 we finally went to a 454 R/V (HD- motorhome) mech pump, with no more headaches. Good Luck.

Re: suburban tow truck fuel issue
 

If the fuel line was tied to the low side AC line it would get cold.

Re: suburban tow truck fuel issue
 

Captain ,, When you get it all figured out call Fred and Jo Anne they got the same problems and would buy cold beer ,,lots of it,,,, for the cure.:cool:

Re: suburban tow truck fuel issue
 

nice to see not only one with issue... thought it was something i did converting from efi to carb for a while but now im just baffled... am considering tapping pickup fitting into bottom of tank and using areomotive setup for pump... sounds like overkill but im tired !!!

captain
thanks guys

Re: suburban tow truck fuel issue
 

Jack, the factory in-tank pump would have made a nice pump with a return-style regulator, using the factory return line. Could have also been used as a booster pump, with a regulator, for the mechanical pump. Guys around here have done it both ways.

Re: suburban tow truck fuel issue
 

yeah ed hindsight is 20 / 20 !!

jack

Re: suburban tow truck fuel issue
 

Check/replace all the flex/rubber line connections, some types of hose can come apart inside or swell blocking flow.

Re: suburban tow truck fuel issue
 

Jack, call me tomorrow.

Been there done that.

I am pretty certain I have a $30 solution for you.

219-8610-1214 after 10am CST