Topic: Fuel pump on ’78 C3 350??
in Forum: C3 Engines
Dave
Lifetime MemberIf you use a 3/8 extention and socket you can sort of guidle the bolts in place. A bit of good dexterity and you can get them started. You can reach in there to do this, but you may need to try from several different approach angles. It's really not that bad.
Just be sure to see the fuel pump push rod is in the up position. If it's down you won't get the pump lined up and the bolts started. You can turn the engine by hand and lift on the push rod at the same time to be sure it is up. To keep it there, there is a bolt in the front of the block that can be removed, and a longer bolt installed finger tight to hold the rod in place.
If it drops and you can't lift it, just take the remaining two bolts off the plate the pump bolts to, and remove the plate. Then you can access the rod. It may fall out. If you don't want to use the bolt to hold it, if you took it out you can coat it with wheel bearing grease and stick it back in place. That will usually hold it up. When you put the plate back, be sure to start the fuel pump bolts, without the pump, to know the plate is lined up when you tighten the bottom plate bolts, or you may stop yourself from getting the bolts started.
I just replaced my fuel pump in my 78,last weekend,the easiest way to get at the bolts for the pump is;remove the wheel,there is an opening were the brake line comes frome the top of the frame to the rubber brake hose,the opening is more than wide enough ,if you look through the opening,you will see the pump right there in front of you ,I used 2 ,6 inch extensions, piece of cake.the thing I had the hardest time with was,breaking loose the nut on the pump where the fuel line attaches,you need 2 wrenches 1 to hold the pump fitting and a flare nut wrench for the line nut,use a liberal amount of PB Blaster and let it soak for a while.I took off the flat plate afterwards and took the pump rod out and greased it and put it back in ,it will stay up for a while.I bumped the engine over with the starter until the rod was in the up position,I have A.C. and a free wheeling fan so I couldn't use the fan blade to turn the motor over by hand.as long as you have the steel line off and the fuel drained out,it's a good time to take the other end of the line at the carb off and change the fuel filter 
.I got my fuel pump and filter at ADVANCE AUTO $27.00 plus tax and about 2 hours install time,it won't take you that long if everything goes smoothly,but it is a 26 year old car,and nothing ever goes that way,good luck ,any problems ,give a shout
C3VR Lifetime Member #93
I'm not even certain the fuel pump is bad, but in a lazy moment last year when I was dropping the ZZ-4 in I reused the old fuel pump rather than making the 20 mile round trip to Advance right around their closing time. REALLY bad brain-fart, should have waited another day.....
Occaisionally when I shower down on it, it seems to momentarily run out of gas for a few seconds then pick back up. I changed out the fuel filter, which helped, but the problem still persists. Might be the Q-Jet. I have the choke plate cranked tightly open, so I don't think it is slamming shut under high air flow.
I'm driving the old rod to Panama City next week and planned to replace the fuel pump as cheap insurance. I'll dig back into it this weekend.
Thanks again!
Dave
That sounds like the acellerator pump in the carb. With the engine off look down past the choke plates. At a moderate speed, fully open the throttle. You should see two continous jets of fuel shoot into the carb. If not, repair the acellerator pump. How? Look at
www.vetteprojects.com under Ken's projects.
Great piece on Q-Jets. I put the site in in my "Favorites" for when I dig into mine. It seems to be doing well now though. Mine is the 800 CFM Q-Jet from the L-82.
I was a little unclear on my problem. When I "run out of gas" the acccelerator pump has already done it's job. It comes out of the hole like a bullet strong as lye soap all thru the 1 - 2 shift then just B4 of after the 2 - 3 shift, it dies MOMENTARILY then picks back up if I stay in it. No problem at all just off-idle. It COULD have possibly been the choke plate slamming shut momentarily under the continued high airflow then opening back up again as the flow died down. I have not really showered down on it since I tightened the choke plate up.
Problem is, it just started doing it a couple of weeks or so ago and I did not notice it between last Sept., when I got the thing back together till recently, the choke plate tension was the same, leading me to the pain-in-the-butt fuel pump.
Under sane driving, no problem, only WOT high RPM incidence. Problem is it's hard to drive sane in that thing and I can just see it embarassingly happening when a Mustang GT or Cobra or Z-28 is next to me leaving the light!! (or driving down I-65 South in Alabama).
Dave
I've been jacking around with the secondary air flap tension for the past several weeks and if anything, it might be a tad tight, but I think I have it about right, there is minimal, if any, bog when the secs kick in. When I started the tension was light and boggy, I'm maybe 1/4 turn, maybe more, past the initial adjustment which is a bunch, I quit counting 10 degree turns in March. As far as I know, the carb has not been kitted or rebuilt. All I did was clean it with "Scrubbing Bubbles", one helluva external carb cleaner. Is the function of the vacuum pull offs discussed in your Q-Jet piece? I just scanned it for a few minutes and saw them mentioned, but not in detail.
My intermittant problem crops up when the secs are wide open in major roaring gas-sucking mode, then dies for a couple of seconds before picking back up again, almost as if the bowls are dry and waiting for food and beer.
I don't file for Social Security 'till October and am kinda pressed for time b4 I head for FL. Once there, we head back up to Ozark, AL, hook up with the locals for a cruise with their bunch back down to Panama City. I just KNOW there are going to be a few races on the way back and want to be prepared! I think I can dust about any C4, maybe even a C5 in the 1/8th with my 3:55 gear vs their 2:59s, if those C5 wimps would ever hit the strip.
I don't want to have to jack it up in Elba, pull the wheel and fix the fuel pump on the road. As a 1943 model, I've done it before, but was a whole lot more flexible and less fat then.
BTW.... I really like the Q-Jet on this setup. 15, maybe more, MPG hwy. under my overweight right foot.
Dave
The front vacuum pulloff is the primary. If you have a rear one, it's the secondary.
The primary is used to open the choke a small amount at startup to prevent it from running too rich until the choke coil starts to open the choke place. The secondary can do the same thing, but it's staged.
Both of these have an additional function. When retracted and fully pulled in by vacuum, the secondaries won't open. As manifold vacuum drops, the secondaries are allowed to open. This is not controlling by the secondaries plates, but the air flaps. If one of these pulloffs is failed, the car can bog.
How much impact will fuel pressure have? Most postings about bog include suggestions to check fuel pump pressure to be in the range of 4 to 6 psi. I also have an Advanced Auto fuel pump that pumps a volume of 12 oz of fuel in 30 sec at 4 to 6 psi. However, the shop manual and Chiltons says my 78 should have 7.5 to 9 psi. I'm working on a bog problem at acceleration and feel it must be a fuel starvation problem.