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I couldn't read the numbers on that gauge. What is the range? Is it a combination fuel pressure, cylinder pressure gauge? Perhaps, after following @leigh1322's instructions, you just need gauge with a lower range.
I’ll run some test when I get time to get some numbers. I agree that the pump rod doesn’t look like it was turning and being stuck backs that idea up. I also thought that scale on the gauge was too broad for an accurate pressure reading. It was the only kit that had the correct firing to do the hookup I was wanting to do.
KC
2020 Corvette of the Year Finalist (performance mods)
2019 C3 of Year Winner (performance mods)
2016 C3 of Year Finalist
I would block the fuel pump off and run an electric pump to make sure its not another issue as well.
Also areyou buying a new pushrod or cleaning up the other. Does it slide in and out freely once you got it freed up? Im curious if the rod is to big of a diameter
I bought a new Comp Cams fuel pump rod, they discontinued the old part. I checked the old rod and it was bent a full 1/16” explaining the sticking. The end isn’t “mushroomed” but dies has a VERY slight worn place from not turning. I’m guessing my fuel pressure gauge is faulty as it shows zero, I unhooked the pump hose, ran the engine and it flowed a healthy amount of fuel into a container. I’ll buy another gauge just to see what the fuel pressure is.
KC
From a completely mechanical aspect I understand those that choose that choose to run an electric fuel pump. My car is very original and part of the joy (and pain) of ownership is getting it to function as it left the factory.
To follow up, I ran the pump with the carb supply hose in a container and it flowed well. I will follow up with a new fuel pressure gauge but feel confident my power issue isn’t fuel flow.
2020 Corvette of the Year Finalist (performance mods)
2019 C3 of Year Winner (performance mods)
2016 C3 of Year Finalist
That was what I was trying to get you to see. YOu need to go in a different direction to figure out your power issue. I would look at carb tuning, dirty internals if its a fuel issue., weak coil, bad plugs or wires and timing for a possible ignition or weak spark issues.
All of those items have been checked.
1. Carb was recently sent to Lars.
2. Dist was rebuilt by a reputable supplier and weights are advancing.
3. Tuned via Lars papers.
4. Coil replaced.
5. plug wires replaced twice.
6. fuel tank and lines are clean.
7. I pulled the valve covers and everything is intact and valves are moving.
8. I started the car at night and didn’t see any arcing.
9. The storage area does NOT have the fuel smell but I do smell rich “un burnt” fuel when driving. Could be a dead or intermittent cylinder but I don’t get any change when pulling each wire with the engine running.
KC
Update:
I purchased a fuel pressure testing kit and only getting 1 psi at idle and maybe 1.5 psi at 3000 rpm. Should I do a road test while the equipment is hooked up? I don’t know if much will be learned for the time.
From my research it sounds like I should be at 5 to 6 psi for the quadrajet, do most “stock” or OEM type pumps do this without a regulator?
Any suggestions for a quality OEM type of mechanical pump? I’m pretty excited to get this on the road with the new pump and see how it performs.
KC
Just curious, I see that your vacuum advance is connected to the CEC Solenoid like it came from the factory. Is the solenoid working properly....higher rpm's at start up for about 15 seconds and higher rpm's in 3rd or 4th gear?
I bought a new Comp Cams fuel pump rod, they discontinued the old part. I checked the old rod and it was bent a full 1/16” explaining the sticking. The end isn’t “mushroomed” but dies has a VERY slight worn place from not turning. I’m guessing my fuel pressure gauge is faulty as it shows zero, I unhooked the pump hose, ran the engine and it flowed a healthy amount of fuel into a container. I’ll buy another gauge just to see what the fuel pressure is.
KC
I would assume a bent pushrod was an installation error.
Could the rod have gotten caught behind the arm instead of on the tip?
Can not think of anything else that would bend 1/2" steel.
When you put a new one in:
Rotate the engine 1/2 turn or so until the pushrod goes all the way in, then pump is easier to screw into place. You can use some grease to help hold it up in the hole, it should be almost flush. There is no screw hole on a BB to help you like on a SB.
It must slide in easily and be able to rotate.
At this point I would seriously consider measuring the fuel pump lobe lift with your finger tip and a remote starter.
You must be getting faster at R&R'ing fuel pumps by now!
Leigh1322, I’m betting with you on the incorrect installation leading to the bent rod. I think all is well now but will order another fuel pressure gauge as I’d like to see what it is under acceleration. My main goal is to figure out why the engine is not accelerating.
Concerning the CEC, I’m studying up on that solenoid and would like to get it working correct. I don’t know if it’s currently working as I don’t know enough yet. I understand it’s a one year part?
KC
Last edited by grumman41; Aug 20, 2024 at 01:07 PM.
A new gauge with a 0-30 scale or 0-15 scale is what you need.
A typical 0-100 or 0-140 EFI tester may not even move the needle at 5 psi.
Me I would probably just change the gauge:
I’m going to be away for about a week but will get a video ASAP. I did get to check the vacuum and it’s only about 8 to 10 at idle. I didn’t have time to block off or isolate the low vacuum issue. More troubleshooting on that when I get back.
KC
Actually that cam is bigger than you think. It's a 230/236 HR on a 110LC.
It might be mild for a race cam, but it is borderline for a nice street cam.
6-8* bigger than a ZZ502 cam. which made 13" idle vac.@ 700, but would be a little more at 850.
See his tuning thread here: Link
6* bigger than my dyno'd solid roller which made 15" vac @ 850
It is basically the same as a LS6 cam, if you measure that after the valve lash. And yours is on a tighter 110LC vs that one's 114LC.
IIRC those made around 13", yours has more overlap than that, so less vac.
My 350 had a slightly larger 239/239* @ 114LC and made 10.5" vac at 850.
I would only expect maybe 10-12" vac max on yours.
That's the range where the idle vac is starting to drop, and very careful tuning is necessary to make it good & streetable.
It's doable but you will have to work at it.
And if might not work well with a Q-Jet!
They have trouble with idle vacs below 13".
Didn't I see a Q-Jet in your pic?
How did it idle on the dyno run? & pick-up with a throttle hit?
It might not have enough fuel from the QJet until it hits the main jetting @ 2800 or so.
Maybe that is why it seems "off"
Last edited by leigh1322; Aug 21, 2024 at 07:25 PM.
Correct, it is the original QJet, it operated like fuel injection on the dyno and has very good off idle response now. The engine just falls off about 2600 to 3000 rpm. It actually pulls ok then starts to fall off. It sounds like my vacuum is still a few inches low. I’ve tested so many things it’s getting pretty limited as to what it can be.
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