Does a Fuel Pump matter?
Thread Starter
Drifting
Joined: Feb 2005
Posts: 1,583
Likes: 5
From: Richardson Tx.
Does a Fuel Pump matter?
I have a mild engine rebuild with a stock fuel pump installed.
Long story short, I think the car is not accelerating worth a darn, and so I am looking for a missing piece of the puzzle. The car accelerates smoothly - no cutting out. its just way slower than I thought it would be.
Could this be a fuel starvation issue - even though it is not cutting out?
Is a stock fuel pump ok to run for a 275-325 hp motor?
thanks!
Long story short, I think the car is not accelerating worth a darn, and so I am looking for a missing piece of the puzzle. The car accelerates smoothly - no cutting out. its just way slower than I thought it would be.
Could this be a fuel starvation issue - even though it is not cutting out?
Is a stock fuel pump ok to run for a 275-325 hp motor?
thanks!
Le Mans Master
Joined: Jun 2004
Posts: 6,231
Likes: 65
From: Seattle WA
St. Jude Donor '14
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
Believe it or not, your problem is likely that the accelerator pedal is not opening the secondaries on your carb. To check it properly, you need to have someone in the car working the accel pedal and you under the hood checking it out.
You can check the car cold or warm; if warm (and the choke works properly) you do not have to manually release the secondary lockout link (on the right side of the carb). If you check it cold, that link must be moved so that secondaries will even open.
Remove air cleaner; verify that lockout link is out of the way so secondaries can open; hold upper secondary air valve fully open with your fingers; look down into the secondaries with a light, if you need it; have helper depress the accel pedal all the way to the floor.
The [lower] throttle valves in the secondaries should open fully...straight up and down. If they do not open or do not open fully, the accel pedal linkage, throttle cable, carb linkage, choke, etc. are suspect for not allowing proper function. This is a very common problem, but is often overlooked. Folks use their hand to exercise the carb linkage to WOT and assume that this will be the same as pushing accel pedal to the floor. It is not the same....
Hope that helps and you find your problem.
You can check the car cold or warm; if warm (and the choke works properly) you do not have to manually release the secondary lockout link (on the right side of the carb). If you check it cold, that link must be moved so that secondaries will even open.
Remove air cleaner; verify that lockout link is out of the way so secondaries can open; hold upper secondary air valve fully open with your fingers; look down into the secondaries with a light, if you need it; have helper depress the accel pedal all the way to the floor.
The [lower] throttle valves in the secondaries should open fully...straight up and down. If they do not open or do not open fully, the accel pedal linkage, throttle cable, carb linkage, choke, etc. are suspect for not allowing proper function. This is a very common problem, but is often overlooked. Folks use their hand to exercise the carb linkage to WOT and assume that this will be the same as pushing accel pedal to the floor. It is not the same....
Hope that helps and you find your problem.
Thread Starter
Drifting
Joined: Feb 2005
Posts: 1,583
Likes: 5
From: Richardson Tx.
I am really stumped over this lack of acceleeration....I verified that the secondaries open vertically when my wife floors the pedal. I have verified timing (32 deg.) for Vortec heads.
Gm Cam # 24502476 - Hydraulic Flat Tappet - 212/222 .435/.460.
Compression test showed all 8 cylinders 180-185psi
In case you are still interested:
Chevy 350 Bored out .020 - Block was not decked.
HypereutecticPistons: (Flattop) Sealed Power# H345NP - Flat Top; 4 valve reliefs
Comp. Ratio - 9:6:1 (I guesstimate)
New 64CC Vortec Heads - not modified
Performance Products Vortec Cyclone #52006 (Edelbroc Performer Clone) –Dual Plane
Total Timing set to 32 deg...all in by 2800 rpm....Initial = 20 deg.
3.36 Rear End gears
2.5 True Duals- no cats – long tube headers - turbo mufflers
4 Speed manual trans.
All emission stuff removed
New plugs (correctly gapped)and new wires (tested)
Q-Jet Carb - I completely went through and rebuilt it using Lars' papers
Primary jets: 73
Primary rods: 41K
Secondary Rods: DR
Secondary Rod Height: 41/64"
Float Level: .420"
idle mixture screws: 4 turns
Secondary windup: 3/4 turn
Gm Cam # 24502476 - Hydraulic Flat Tappet - 212/222 .435/.460.
Compression test showed all 8 cylinders 180-185psi
In case you are still interested:
Chevy 350 Bored out .020 - Block was not decked.
HypereutecticPistons: (Flattop) Sealed Power# H345NP - Flat Top; 4 valve reliefs
Comp. Ratio - 9:6:1 (I guesstimate)
New 64CC Vortec Heads - not modified
Performance Products Vortec Cyclone #52006 (Edelbroc Performer Clone) –Dual Plane
Total Timing set to 32 deg...all in by 2800 rpm....Initial = 20 deg.
3.36 Rear End gears
2.5 True Duals- no cats – long tube headers - turbo mufflers
4 Speed manual trans.
All emission stuff removed
New plugs (correctly gapped)and new wires (tested)
Q-Jet Carb - I completely went through and rebuilt it using Lars' papers
Primary jets: 73
Primary rods: 41K
Secondary Rods: DR
Secondary Rod Height: 41/64"
Float Level: .420"
idle mixture screws: 4 turns
Secondary windup: 3/4 turn
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
Does it 'sound' like the Q-jet's secondaries are opening when you hit the throttle? If it is just not accelerating, the timing must not be advancing as it should. Is it acting differently than before (with the same build)?
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Safety Car
Joined: May 2004
Posts: 4,363
Likes: 1,588
From: los altos hills california
With regard to the title "does a fuel pump matter" I managed (rather my car did) find a way to disable the pump. I put in a new roller cam and other stuff and also switched to Mobil 1 (what could be better, right?). Well over time the fuel pump lobe managed to round off to the point where the pump stopped pumping an adequate supply of gas. Either the the cam wasn't properly hardened or the lack of ZDDP protection was at fault. Took me a while and another pump and finally a dial indicator to believe and correct the problem.
Now I'm not saying this is what's happened to you but when things like this happen to me, the phrase "the sheer perversity of inanimate objects" comes to mind. Bizarre stuff like this is not outside the realm of possibility. It's easy enough to check the pumping capacity but surprise things weren't what they seemed. Fixed with a new cam, different oil, and a bronze tipped fuel pump rod.
Now I'm not saying this is what's happened to you but when things like this happen to me, the phrase "the sheer perversity of inanimate objects" comes to mind. Bizarre stuff like this is not outside the realm of possibility. It's easy enough to check the pumping capacity but surprise things weren't what they seemed. Fixed with a new cam, different oil, and a bronze tipped fuel pump rod.
Le Mans Master
Joined: Jun 2004
Posts: 6,231
Likes: 65
From: Seattle WA
St. Jude Donor '14
Let's back up for a second.
Has the car ALWAYS deliverd less acceleation than expected?
Timing - 20 degrees initial seems a bit much to me, and I would take it out to 36 degrees if it doesn't ping, removing the limit bushing if it's in place to end up with a lower initial. I tend to do this if I have over 14 initial, but I know Lars doesn't see a problem with higher initial - so I'd take that particular recommendation with a grain of salt
But overall, I'd take another look at that curve.
No filter in the Q-jet body, right? Especially the bronze one?
You also checked the PRIMARY throttle butterflies, right? The secondaries would give a huge flat spot if they're not opening correctly, but if the accel issue is right from off-idle, I would look elsewhere first.
After all this, worth taking a look at fuel pressure...but I don't think that's the culprit.
All just thoughts on other things to check
Has the car ALWAYS deliverd less acceleation than expected?
Timing - 20 degrees initial seems a bit much to me, and I would take it out to 36 degrees if it doesn't ping, removing the limit bushing if it's in place to end up with a lower initial. I tend to do this if I have over 14 initial, but I know Lars doesn't see a problem with higher initial - so I'd take that particular recommendation with a grain of salt
But overall, I'd take another look at that curve. No filter in the Q-jet body, right? Especially the bronze one?
You also checked the PRIMARY throttle butterflies, right? The secondaries would give a huge flat spot if they're not opening correctly, but if the accel issue is right from off-idle, I would look elsewhere first.
After all this, worth taking a look at fuel pressure...but I don't think that's the culprit.
All just thoughts on other things to check
Thread Starter
Drifting
Joined: Feb 2005
Posts: 1,583
Likes: 5
From: Richardson Tx.
Since I completed the rebuild it hasn't ever accelerated like I thought it would. I've been double-checking all that I know since then.
I am not sure whether or not I can "hear" the secondaries open. Would you say it is an unmistakable sound?
Yes- I verified the Primaries fully open when my wife holds down the throttle.
Yes- I have a Fram paper type fuel filter installed - about 2.5 inches long. Is there something wrong with having the internal fuel filter installed?
The only reason that I have 32 deg. total timing is because I've read so much that 32 is all that is needed for Vortec heads. I'm open though.
Yes - thanks for the replies. I am looking for ideas that I haven't thought of. On paper I would think that what I have installed should make the car run very well. I think my Buick could take my vette in a 0-60.
If you have any other thoughs please share.
Rob
I am not sure whether or not I can "hear" the secondaries open. Would you say it is an unmistakable sound?
Yes- I verified the Primaries fully open when my wife holds down the throttle.
Yes- I have a Fram paper type fuel filter installed - about 2.5 inches long. Is there something wrong with having the internal fuel filter installed?
The only reason that I have 32 deg. total timing is because I've read so much that 32 is all that is needed for Vortec heads. I'm open though.
Yes - thanks for the replies. I am looking for ideas that I haven't thought of. On paper I would think that what I have installed should make the car run very well. I think my Buick could take my vette in a 0-60.
If you have any other thoughs please share.
Rob
Le Mans Master
Joined: Jun 2004
Posts: 6,231
Likes: 65
From: Seattle WA
St. Jude Donor '14
The Q-jet filter can cut flow to an extent that causes issues in some cases. I know with original lines there's nowhere to put a larger filter...but I would inspect the filter...and maybe make a few quick runs without it just to see. But since it's the Fram and not the bronze one...not as likely.
The secondaries in a Q-Jet definitely make a sound The exhaust note deepens a bunch! I grew up on that sound and it's unmistakable!
I would take another look at the curve - I agree that Vortecs typically require less total advance...but that's something to sort out on the dyno, and do a very standard curve to sort this out. You have vacuum advance as well? What distributor?
How did you "guestimate" the CR?
Sorry to play 20 questions - this would be easier sitting in my driveway More beer, too...
The next step IMHO would be to get on the chassis dyno. It's $250 well-spent regardless, and I'd be 100% they would find the issue.
The secondaries in a Q-Jet definitely make a sound
The exhaust note deepens a bunch! I grew up on that sound and it's unmistakable!I would take another look at the curve - I agree that Vortecs typically require less total advance...but that's something to sort out on the dyno, and do a very standard curve to sort this out. You have vacuum advance as well? What distributor?
How did you "guestimate" the CR?
Sorry to play 20 questions - this would be easier sitting in my driveway
More beer, too...The next step IMHO would be to get on the chassis dyno. It's $250 well-spent regardless, and I'd be 100% they would find the issue.
Team Owner
Joined: Apr 1999
Posts: 21,953
Likes: 1,445
From: Reno Nevada
2024 C3 of the Year Finalist- Modified
Years ago I bought a pot metal roller cam from Comp cams. This was before they told you to use a bronze or roller fuel pump rod. The cam lobe for the fuel pump went to mush.
I thought I had a fuel pump problem because of lack of pressure. I replaced the pump never thinking of the cam
I thought I had a fuel pump problem because of lack of pressure. I replaced the pump never thinking of the cam
Melting Slicks
Joined: Aug 2008
Posts: 2,200
Likes: 3
From: Lehigh county Pennsylvania
Not where I come from.Your initial + mechanical + vacuum should be closer to 50 degrees total advance. No wonder your performance is close to that of a wound up rubber band.
Last edited by 69 Chevy; Jun 13, 2012 at 11:15 AM.