fuel pump dying?, timing off? or....?

[woobie1966]

My big block is giving me trouble, every now and then when hitting the gas while driving it will stutter, i believe the source to be a failing fuel pump, but could it be timing? it doesnt happen every time. I had also read a thread about msd units failing (i have an msd 6)
any thoughts would be appreciated
mike

 

[vette-dude]

Might be a dirty fuel filter. either the one in line or the bronze element on the inlet of the carb. Just a thought.

Randy

 

[JohnZ]

Does it "stutter" instantly, as soon as you hit the pedal, or does it respond normally and then stutter after it takes off and winds up?

 

[74bigblock]

Mike,

First thing to check is fuel delivery... it's the easiest to check.

1) Check with a flashlight the bottom of your gas tank (inside) and look at the sending unit sock. If there is "stuff" on it... that may be an issue, and should drain the tank and clean the sending unit, or just replace it. There is a special tool you will need to remove the sending unit if needed. It can be found at any of the main suppliers, and also locally at like Napa and the like. Also, be sure to look for rust at the bottom of the tank! (I ended up chasing a bog myself for over a week... turned out to be rust from the tank got up into the fuel system, through the filter and into the carb. I had to replace the sending unit, the pump, the filter, and all the soft fuel lines).

2) Check around the fuel pump for gas/oil residue. There is a small hole at the top of the pump near the block mount. This hole is there to let out extra fuel that is caused by the pump failing/getting stopped up by "stuff".

3) As someone else mentioned, check your fuel filter. If you don't know, or don't remember the last time it was changed... just change it.

Once you have inspected the fuel system, and everything looks good, then I would check the ignition system. It may be as simple as a fouling plug or bad plug wire. Our 454's tend to cook the wires easily, especially if you are running aftermarket headers. If neither of these solve your prob, then I will defer to those with more knowledge of MSD ignitions (as I run a regular distrib with HEI, and have never messed with MSD (except the Chinese food kind; Oh wait... tht's MSG!).

Good luck, and let us know what is going on!

-Dave

 

[RodsnRides]

Agree with all of the above. If you have a vacuum/pressure gauge, pull the line off the carb and make sure you are getting the 5-7 psi (or what it should be, anyways). Check your distributor-both mechanical and vacuum advance-you may have a weight hanging up. Look in the carb throat and give the throttle a couple of pulls-you got a good squirt going on (accelerator pump)? Also might want to recheck your timing and make sure the distributor and hold-down clamp is tight-I have seen them back off as well. Good luck.

Rick

 

[GTR1999]

If you're running the stock pump check to see if the S hoses are still there or if reg gas hose is used. I've had fuel feed problems from using regular gas hose instead of the molded S hoses, the hose will kink and stop flow.

 

[woobie1966]

Thanks for the input,
I neglected to say I had the same problem about a month back, replaced the inline fuel filter and I thought I had it licked. I will check the gas tank next for rust/trash, I have a holley double pumper (not sure cfm) where would the filter in it be located?
If these dont pan out, ill check the plugs, I had the headers jet hot coated, so they are a bit cooler but you never know.
thanks all ill let you know what I find
mike

 

[tomtom72]

Hi Mike, On a holley the bronze filter is at the float bowl in-let. If you have a dual feed then each bowl in-let will have a bronze filter. Just remove the feed line or lines and the fitting that is left on the bowl in-let is 5/8"(?) and it comes off and the filter usually comes out with the fitting. The filter is directional, I believe, so mind what the orientation is. It has a depression on one side and a funnel or cone structure on the other side. I don't remember exactly as it has been a long time since I took apart a holley. Good luck in finding the problem! Tom

 

[woobie1966]

ok ,

finally got time to check on issues discussed, heres the rundown:
-checked fuel tank, netting around inlet appears ok, though there is some rust on the bottom of the tank
-sprayed top of fuel pump, seems clean, no major deposits of gunk
-checked distributor, is tight
looked at carb with air filter off, appears I may have been wrong about having double pumper, as i give it gas only two squirts of fuel are showing
tomorrow i'm going to check the filters in the carb, any suggestions on keping the gas mess down (when i changed fuel filter it kept oozing fuel)
if the filters are clean, i guess my last option is to get timing checked
i dont have a timing light, or know how to check it any way
anyone know of a good tune up guy in the ft lauderdale area?
thanks
mike

 

[photovette]

My '77 started doing the same thing Friday--a prolonged (1/2 second) hesitation when applying light gas pedal. During the day it got worse--severe hesitation when going to WOT.

I got a can of carb cleaner and gave it a good spraying. I just took it out and barely made it home--started out okay, then got rapidly worse (within 20 minutes)-- no power at all now--it's top speed is 40 mph. Yep, I got a 'vette that does zero to 40 in about 30 seconds...

Idles just fine, but no power--zip.

The carb (Edelbrock Qudrajet 1903) and fuel pump are about a year old. I replaced the filter about a month ago. Distributor, plug wires, plugs all two months old.

I did fill the gas tank right before it started acting up, and it's got steadily worse as the fuel level dropped.

I'm calling the gas station now and taking it to the shop on Monday.

 

[ON 7TH]

dry rotted fuel lines will cause that problem,remove the rubber boot around the filler neck & check em

 

[74bigblock]

i'm going to check the filters in the carb, any suggestions on keping the gas mess down (when i changed fuel filter it kept oozing fuel)

Mike,

I used a clamp on one of the rubber hoses to crimp off the flow of fuel, then started the car and ran that portion of the line dry. When the car stopped running, I knew the line was empty. I would recommend crimping the feed line to the pump... that way you don't over pressurize the lines.

Dave

 

[woobie1966]

thanks dave,

sometimes the obvious lips through my mental grasp!
If the carb filters are clogged can they be cleaned/re-used?
If not how do I find out what carb I have? where do they stamp the model # on holleys?
mike

 

[74bigblock]

You bet.

Sorry, I can't help you out much on the holley.... I run an Edlebrock 750. They are much easier to maintain and rebuild. From what I understand, there is a filter plate right behind the fuel line fitting. It's just a wire screen if I remember correctly. This is re-usable.... just soak it in carb cleaner.

-Dave

 

[motorman]

My big block is giving me trouble, every now and then when hitting the gas while driving it will stutter, i believe the source to be a failing fuel pump, but could it be timing? it doesnt happen every time. I had also read a thread about msd units failing (i have an msd 6)
any thoughts would be appreciated
mike

if your fuel pump has a return line to the tank just squeeze the rubber hose closed with a small "C" clamp and see what happens. this return line is a calibrated leak and shutting it off will increase the fuel flow and pressure to the carb so if the pump is getting weak this will fix the problem. been there done that to get home on a failing fuel pump

 

[woobie1966]

Holy crap!!! I just went outside to check the logistics of crimping off the fuel,and for poops and giggles I checked the oil level (has not been started since yesterday evening). I had a grand total of two drops of oil on the dipstick!!!. I dont know if the two items are related, but i think i better get some oil in the engine (first things first), any suggestions on a gradeof oil/make for the filter? original internals as far as I can tell. Ps the few times i have gotten on it I have never seen white smoke, only some black (carb tuning) what the he## happened to all my oil??

As soon as you guys give me a recommendation, im out the door for the oil/filter

thanks mike

 

[Hib Halverson]

My big block is giving me trouble, every now and then when hitting the gas while driving it will stutter, i believe the source to be a failing fuel pump, but could it be timing? it doesnt happen every time. I had also read a thread about msd units failing (i have an msd 6)
any thoughts would be appreciated
mike

Typically, a "stutter" or a flat-spot (also called a "sag" or just "poor throttle response) is not usually caused by a bad fuel pump or, at least---if there is a bad fuel pump, you'll experience a lot of problems other than just a flat-spot.

First thing I'd do is check the general condition of the ign. Check the timing, make sure the plugs and wires are ok, if it has a point-type distributor, check the points and their dwell setting. Make sure the vac. advance is working properly. Make sure the ign. coil and all primary ign. wiring (incl. that of the MSD) are in good condition.

Once you validate those things, start looking for a carburetor problem, especially one with the accelerator pump.

Also, if the problem is intermittant, it's probably not the fuel pump as a failing (or failed) fuel pump is going to affect the engine all the time. A more obvious sign of a failed fuel pump will be loss of power at high rpm in higher gears, constant "vapor lock" and obvious. fuel leaks from the fuel pump body. Also, if the pump fails a volume test, that's indicative of the pump going away.

Lastly, a problem with the MSD ign. unit, while possible, is not likely to produce a flat-spot. Usually, when an ign. amplifier fails, the engine quits and won't run.

 

[wishuwerehere82]

Holy crap!!! I just went outside to check the logistics of crimping off the fuel,and for poops and giggles I checked the oil level (has not been started since yesterday evening). I had a grand total of two drops of oil on the dipstick!!!. I dont know if the two items are related, but i think i better get some oil in the engine (first things first), any suggestions on a gradeof oil/make for the filter? original internals as far as I can tell. Ps the few times i have gotten on it I have never seen white smoke, only some black (carb tuning) what the he## happened to all my oil??

As soon as you guys give me a recommendation, im out the door for the oil/filter

thanks mike

Yep, oil pressure might be a little low with that level.
I use Pennzoil 10W30 with a WIX filter, but an A/C Delco filter would do in a pinch. Let us know how it goes after the oil change.

 

[woobie1966]

You know whats funny though, the oil pressure gauge always shows good, i have read bad things about original gauges...hmm now I know why
off for 5 qts and filter.....
ps does anyone think this might have something to d owith original isue?
mike

 

[Jack]

My '77 started doing the same thing Friday--a prolonged (1/2 second) hesitation when applying light gas pedal. During the day it got worse--severe hesitation when going to WOT.

I got a can of carb cleaner and gave it a good spraying. I just took it out and barely made it home--started out okay, then got rapidly worse (within 20 minutes)-- no power at all now--it's top speed is 40 mph. Yep, I got a 'vette that does zero to 40 in about 30 seconds...

Idles just fine, but no power--zip.

The carb (Edelbrock Qudrajet 1903) and fuel pump are about a year old. I replaced the filter about a month ago. Distributor, plug wires, plugs all two months old.

I did fill the gas tank right before it started acting up, and it's got steadily worse as the fuel level dropped.

I'm calling the gas station now and taking it to the shop on Monday.

If the gas is OK ... 77 has HEI dist ... consider the plug-in ignition module beneath rotor ... readily available, cheap & easy to replace. Bad module can act up as you describe.
JACK:gap