Greetings, I recently had a small coolant leak so I took the car to a mechanic and they replaced the whole radiator. Anyways when driving the car home from the shop I noticed when I press the accelerator pedal down to the floor in wide open throttle that in between 3k-5k somewhere is when my problem occurs. I experience a loss of acceleration in these high RPM/s only when the throttle is wide open. I honestly don't know the correct term if it is a bog, sputter, ect. All I know is it feels like I hit a rev limiter and just lose acceleration power. Now if I baby the gas pedal I have no issue, Again this is only @ WOT.

I tried my best to do some research and came across quite a few things to help me understand what it might be and learned it sounds fuel related. Then I remembered these corvetteforums. anyways just to make sure It wasn't something small I did replace some things to try and do a tune up. So over the weekend I Installed new spark plugs, new spark plug wires, The dist cap looks clean/new so i didn't replace it. didn't even bother to check the rotor because few years ago I put in a whole new MSD HEI distributor in. I seen a post somewhere to try and replace the HEI coils, and I seen a video on youtube where someone had a similar issue and they replaced the coils to fix there problem they said they had the radiator replaced and the same prob occurred and a new coil fixed it. I was thinking about buying a MSD coil anyways. Also another thing I'm about to do is the air filter and fuel filter. I would take it for a test run after but its raining pretty bad here today so I'll have to wait to be safe. also the more research I do and keep coming across deferentially makes me think its fuel related maybe too lean, but I really am not sure.

 

Well if you dont know when the fuel filter was last changed that would be an excellant place to start.

 

Thanks for replying I changed the fuel filter last about 2 years ago I think?

Everything I mentioned above I changed already and test ran with the problem still occurring.

Except for the Air filter & Fuel Filter. I changed those today but its too much of a overcast for a test run. the Fuel filter wasn't really that dirty still could see the yellow part a bit in the filter it's just a little darker not too dark tho but it was tinted dark. now the Air Filter top was pretty dirty. Also I just put on a new oil cap breather not that it should matter but just to make sure. Then I ordered a new MSD HEI coil and MSD HEI BUSHING spring. and MSD Rotor today also. but it wont be here to install till weekend i'm expecting.

 

Dirty filter could be the problem, not enough air and too much fuel..

 

Do you mean that the loss of power occurs just as you floor it, or do you mean that after you have the pedal down for a few seconds and the rpm's rising the power loss occurs?

 

I know you may not like the idea but to check the fuel filter properly, drain all the gas out, put it to your mouth, and blow through it. It should feel unobstructed. In addition if you have a plastic see through filter replace it with a metal one.

 

Pop the dizzy cap and check for corrosion on the terminals. Even if it has low miles, moister will mess up the contacts.

 

Thanks for the reply everyone. Still having problems really bad now. OK so I just came back from a test run. Now the problem seems to be a bit worse. I couldn't even drive it in 3rd gear because it would just loose RPM/s all together when I gave it any gas I had a hard time getting it home actually coming up the hill where i live at the top it stalled out on me. I had to wait about 5mins and try and pump the gas just to get it to start back up and baby it to my house...ok so UPDATE on what I just now replaced today.

New Oil breather cap. New air filter top. New Fuel Filter. New HEI Coil. New Rotor.


@widowmaker221: New air filter and fuel filter I even tried running it with out the air breather on to see what it would do same issues still occur.


@jnb5101: Before It only seemed just when I had my foot to the ground but now today it seems to be when i give it gas all together pretty much. I have to really really baby the pedal to even get it going if i press the gas pedal just a tad bit it cuts off the acceleration of RPM/s all together. and if if even go half in or over more than half the pedal pressed in all the way the same thing loss of acceleration RPM/s feels like its gonna choke and die. like it did coming up the hill on my way home. I was scared thought I was gonna have to have it towed but I sat there for a about 5mins and then pumped it and it started up enough to where I could just make it home. Now I'm afraid to even try and test drive it again. so pretty much under 5% pedal pushed it stalls out and over 50% pedal pushed in it stalls out also.


@MelWff: I took the old fuel filter out the carb and put a brand new one in the other day. I looked for the old one and did what u said to try it had no restriction was like blowing threw a new one. It really wasn't that dirty as it was only maybe a year or two old.


@hugie82: when I put in a new coil and rotor I checked the cap it's like new.

 

It sounds like fuel starvation. Check the sock in the tank, kinks in the rubber hose from the tank to the hard line and the "s" hose from the hard line to the pump. By check, I mean remove it and check the inside. Then check the fuel pump pressure at varying engine speeds. Then look to the carb for dirt, residue, plugged channels, needle and seat operation and float position. Did insert the fuel filter correctly?

 

My guess is bad fuel pump.

 

Hey thanks for the reply I was actually thinking It possibly is fuel starvation. some where in that area anyways. since the ignition all seems to be good. I first thought it might be the fuel pump itself. I was hoping it was something minor and easy I could get too because I know that the pump is in the tank and for me that is a little hard too play with, being I really have no tools or jacks to get under there and not any experience in removing a gas talk either. Since I'm not trying to do all that. I'm gonna have to have it towed to a new mechanic that will be willing to work with me when I speak to one. also since it does not feel drivable to me I really don't know how I would be able to test the fuel pressure at varying engine speeds. I was actually thinking it would be good idea to check the fuel pressure tho I don't know what it should read I would like too to make sure that's it, but I don't have a fuel pressure check gauge or know what one I would need and driving it to check pressure is not gonna work since the problem is pretty bad and I don't want to make things worse can i check pressure in park? I was thinking to check the tuning of the idle mixture screws with a vacuum pressure gauge on the carb from reading around on here too. Not sure if that would cause the symptoms I have or or not tho. I don't have a timing light on hand but was thinking to check that too do you personally think this issue could possibly be from my timing going out of place a friend thinks it might be from the timing. I think its Fuel related tho maybe a/f ratio is off. idk starvation sounds like that might be what its doing tho, anyway to check the fuel pressure with out driving it to see if that its fuel starvation. I seen they have small lil inline fuel pressure gauges but dunno if i need to be driving to know. I really appreciate all the help on here from everyone tho I'm still learning. Also just now brought to my attention. I was going over my invoice repairs from last year and see on here they put "Fuel leaks appears to be coming from the fuel pump and steel line" but they didn't replace either one. what it says put here on the invoice is " Steel fuel line is leaking. Repaired steel line with piece of stock rubber line & (2) clamps " no mention of anything else about fuel. that was from last year tho It actually did sit there a whole year because I had a radiator leak and when I got it back 6 months later I had to take it back because it was still leaking. Well u can already guess I'm not going back there. Anyways just trying to see what else this acceleration loss could be from before I take it somewhere. I'd like to be able to see if its something I could fix myself like the timing or idle mixture I'll have to take it somewhere to have the stuff inside the gas tank checked what else really is there that it could it be I can look over under the hood.

Edit: fuel filter was inserted correctly

 

I really am starting to think so but I want to test fuel pressure to make sure, but I can not seem to find a Schrader valve anywhere under the hood to hook up a test gauge how can I test it without one?

Also if its not the pump could it be my timing or Idle mixture screws need adjusted?

 

I believe that your car has a mechanical fuel pump (unless a previous owner changed to an inline electric pump). The pump should be easily found at the pass side front of the engine-follow the fuel line. There isn't any connection for a fuel pressure gauge, unless as above, a PO added one. Don't start messing with the timing or idle adjustments. If you don't have the experience or equipment to check fuel pressure, have someone do it for you.

 

I thought the fuel pump was inside the tank are you saying its easily replaceable under the hood? I'll have to look again. I only know how to check fuel pressure from a Schrader valve but I would like to learn if it still can be done with out one also I rather not have it towed to check for fuel pressure and have a new pump put in if i can easily do it with out going underneath the car. btw if i forgot to mention it's a '79.

Side note: I have everything ignition wise replaced already with all new parts except the Ignition Control Module I had one of those go bad before and the car wouldn't even run so not sure if they go bad slow or just completely stop working. so if you think that it wouldn't be that we can rule out ignition I had it timed a few years ago after putting a new dist in (I was just wondering if it was accidentally bumped or turned out of place it would cause the issues.) so it would have to be fuel ?

 

Follow the fuel line that feeds the carb. It probably drops down the right front corner of the engine and leads to the mechanical fuel pump. I still think that is your problem. You can change the pump with no more trouble than installing an in line gauge. Just get a stock replacement type.

 

hey thanks for that info sounds cake. now my question is how would i go about doing a inline gauge to make sure it is the pump I would really like to check the pressure before replacing the pump tho I do believe it has to be the pump. I just can't seem to figure how how I would test the pressure all i can see is 15psi inline gauges that have no instruction on how to install wouldn't my pressure be above 15 and break the inline gauge do they have something I can screw in to the fuel filter port screw that i can use as a inline gauge or do i have to unclap the rubber hose from that and use a 2nd small fitted rubber hose.

 

The pressure should be about 6 psi. You can T off the rubber line, but be careful-you don't want a geyser of fuel squirting on a hot engine. My advice is to get some help with this from a friend that has more experience than you have.

 

Max, I skimmed the post, so apologies if you already checked this - I didn't see what year yours is, but if it's a'73 or similar with a filler-cap on the top centerline of the vehicle, take a flashlight and look closely at the sock through the filler cap, and the tank surrounding it. About a year ago, I had a similar problem which progressively got worse it seemed - and it was due to a rusty gas tank, which had rust-dust that caked up on the fuel sock. So, at a specific RPM (2300 or so I believe) it would start starving for fuel and around 2700 or so it would drop rpm down and sputter until it refilled the bowls or what not.

Chances are if you see any significant rust in that tank, you'll want to look more closely at that.

 

Do you mean look down in the tank with a flash light under the gas cap? some one mentioned checking the sock and removing the tank previously but I really am not accessible to do all that. I would have to take it to a shop for that to be looked over, but thanks for the input I can ask after i get it running to take it somewhere.

 

6 psi with the car running or just with the key turned to accessory?

does this look like the right thing to use

http://shop.advanceautoparts.com/p/s...013/22906125-P

I'm assuming I would install that somewhere in-between the fuel filter and fuel pump would i need to cut the line to do so? I'm looking at a new pump and see they even have new fuel lines from the carb to pump also on corvettecentral.com looks like installing a new line and pump would be very easy to do from looking at this diagram https://i.imgur.com/puflIfT.png not sure if i need to cut the line or theres a part where i can slip it in if its not all a complete steel line.

also when I do change the pump I see they have plastic fuel line clamp sets I'm assuming it would be placed on a fuel line somewhere before the it reaches the pump not sure where i'll need to do more research but could I use that to also install the inline pressure gauge also to prevent gas coming out. and when u say gas will come out do u mean it comes out as much as it does when replacing the fuel filter or way more? because when I did the filter there wasn't really that much that came out.