Issues with bogging and suspected fuel pump output...

[Oystercopy]

Hey guys.. several years ago, I upgraded the cam with a Comp Cam kit, for slightly better performance on the 440. I believe the lift was .477, so not super radical. However, since adding the cam, I've had a runnability problem, where the engine will not rev above about 3000rpm and bogs on acceleration. A couple of years ago, I also added a new Holley Fuel Pump, since the OEM one died on me, which did not change the bogging issue. So, at least I believe the carb is getting a good supply of fuel. Also replaced the carb with a brand new Edelbrock 750 and only ever ran non-Ethanol gas in the car. So, my question is, did I need to possibly add a higher output pump to the engine when I upgraded the cam? The bogging seems like its not getting enough fuel? If I get a fuel gauge and test it, my understanding is that it should have about 5-6psi in pressure. Lets assume that's the case, is that enough for a cammed engine and could it be I'm simply not getting enough fuel to the carb? Any help greatly appreciated!
OC

 

[Steve340]

Do the test first. I understand the Edelbrock carb will operate no problems with 5-6 psi under driving conditions.
Given your 3000 rpm issue you need to mount the gauge where you can see it and go for a drive.
If the fuel pressure is maintained your problem is not fuel supply.

 

[Oystercopy]

Thanks Steve.. I'll give that a shot!
OC

 

[Ricks72Chlgr440]

Hey guys.. several years ago, I upgraded the cam with a Comp Cam kit, for slightly better performance on the 440. I believe the lift was .477, so not super radical. However, since adding the cam, I've had a runnability problem, where the engine will not rev above about 3000rpm and bogs on acceleration. A couple of years ago, I also added a new Holley Fuel Pump, since the OEM one died on me, which did not change the bogging issue. So, at least I believe the carb is getting a good supply of fuel. Also replaced the carb with a brand new Edelbrock 750 and only ever ran non-Ethanol gas in the car. So, my question is, did I need to possibly add a higher output pump to the engine when I upgraded the cam? The bogging seems like its not getting enough fuel? If I get a fuel gauge and test it, my understanding is that it should have about 5-6psi in pressure. Lets assume that's the case, is that enough for a cammed engine and could it be I'm simply not getting enough fuel to the carb? Any help greatly appreciated!
OC

You had the problem begin after changing the cam. Did you degree the cam or stick it in "dot to dot"? If the latter you'd be surprised at how off the marks on the gears are. I had a guy build my 440 and it ran like a dog. Ended up going to a different block using the same cam & heads... but the machine shop degreed the cam. He said the gears installed at "0" were quite retarded according to the cam card so he advanced the cam 6* as I recall. Day and night difference. Don't always blame the fuel system for runability issues until all other areas have been examined.

 

[Xcudame]

To Rick's point, new camshafts need to be degreed in. Some of the timing gear sets are also a couple degrees off. Since it bogs with two different carbs, I'm thinking install timing is the culprit. Comp cams are OK, but there are better out there (Hughes camshafts come to mind). Lunati Voodoo cams are awesome, but sense Comp cams bought Lunati, the Voodoo cams are going away. Ultradyne cams are good.

 

[Oystercopy]

I didn't put the cam kit in myself, so I don't exactly know how it was done. But the guy was an experienced engine builder and looked at the engine later and (seemed to) confirm that there was nothing wrong with the cam. But I hear what you're saying and if the fuel pump pressure yields nothing, we may have to go back to that and look at it again.

 

[Xcudame]

Could it be a partial plugged pickup screen in the fuel tank? Fuel pressure gauge will probably answer that question.

Correct me if I'm wrong but here's what I'm reading.
Car ran fine before camshaft swap
Car bogs and doesn't run over 3000 rpm after new cam
Swapped fuel pumps, no change
Swapped carburator, no change

Why did the OEM fuel pump die on you?


Assuming no other changes, and the fuel pressure winds up being OK, the timing between the camshaft and crankshaft can still be off. Even experienced engine builders make mistakes. We're human!

 

[Oystercopy]

Yes, XCuda, all true and accurate. I know that the Fuel Tank and Sending Unit were replaced before I bought the car, probably going back about 15-20 years at this point, by the previous owner. That doesn't guarantee anything of course, but at least we know it wasn't the OEM parts still in the car! I'm going to find some time and put the Fuel Pressure Gauge on the car and go from there. I'm not sure that I can have it with me in the car itself while I drive it, to see if it drops while driving. But I was thinking that maybe I could put my GoPro under the hood and have it watch the gauge for me as I drive... who knows.

The original pump in the car was replaced because it started to fail and the engine would die. Luckily, I had one of those plastic, see-through filters on the car at the time and we would watch it empty and of course, the engine would die. So we replaced the pump. But I was having this bogging issue both before and after the pump failed, so who knows.

And of course, it is still possible that the cam timing could be off. If all else fails, I guess I'd have to go back into it to do that work, but not looking forward to it... UGH...

 

[Steve340]

Yep don't have the fuel gauge in the car. Either strap it to the cowl vent or your camera idea sounds good.
I would be quite surprised if the cam timing is the culprit of the bog or the will not rev past 3000 issue.
If the cam timing is off enough to cause a problem the engine is really badly affected - very hard to start etc.

Just one thing to check - are all 4 throttle butterfly blades able open correctly at full throttle?

 

[Steve340]

Just a thought to keep in mind. You may have 2 completely separate issues causing your problems.
For example the carb accelerator pump is causing the off idle stumble and the ignition is the reason it won't rev over 3000 rpm.

 

[Xcudame]

Good point Steve340, he may have two completely separate issues like you indicated.

The GoPro solution sounds effective and safe to me for watching the fuel pressure gauge!

 

[540HemiCuda]

Checking whether your carb is getting enough fuel is simple enough. Many parts stores will rent a vacuum/pressure gage. Just 'T' it in anywhere between the pump and carb. Then you can take a length of hose from the 'T' to the gage which I usually just tape to the windshield where I can watch it while driving. Quick, cheap, and effective. You are looking for very low fuel pressure or pressure that drops significantly with RPM if fuel delivery is the root of your problem.

Even if the pressure is not as high as it should be, the carb will need to run low on fuel in order for the engine to exhibit your operating issues. So, the pressure would need to be far below the recommended pressure or non existent.

Fuel deliver issues usually present themselves after a few seconds of high demand. Not usually initially. Never say never, but not usually right off the bat. There should be enough fuel in the bowls to run the engine for a short time at higher load before a lack of delivery starts to lean the mixture to the point that operating issues become apparent.

 

[Mascottrepair]

Hey guys.. several years ago, I upgraded the cam with a Comp Cam kit, for slightly better performance on the 440. I believe the lift was .477, so not super radical. However, since adding the cam, I've had a runnability problem, where the engine will not rev above about 3000rpm and bogs on acceleration. A couple of years ago, I also added a new Holley Fuel Pump, since the OEM one died on me, which did not change the bogging issue. So, at least I believe the carb is getting a good supply of fuel. Also replaced the carb with a brand new Edelbrock 750 and only ever ran non-Ethanol gas in the car. So, my question is, did I need to possibly add a higher output pump to the engine when I upgraded the cam? The bogging seems like its not getting enough fuel? If I get a fuel gauge and test it, my understanding is that it should have about 5-6psi in pressure. Lets assume that's the case, is that enough for a cammed engine and could it be I'm simply not getting enough fuel to the carb? Any help greatly appreciated!
OC

Hope I'm not late, but it sounds like you’ve covered a lot of the basics already. If fuel pressure checks out around 5–6 psi, you’re probably okay on pump output. But with a cam upgrade , your issue might be more about timing,jetting, or even vacuum advance rather than just fuel pressure. Could also be a mismatch between the cam and carb tuning. A fuel pressure gauge is a good next step, but you might want to double-check your ignition curve and make sure the distributor is dialed in for that cam.

 

[Oystercopy]

Thanks for all the excellent replies people! And YES, Mascottrepair, the distributor is the ONLY item not replaced under the hood, ignition-wise. I had one guy mess with the distributor weights and lock them out, in an attempt to get better runnability. The engine has not stalled or died since he did that, but it comes close. And I don't think locking out the weights did anything for the non-rev over 3K either... I sure hope I don't have to go back in to degree that cam again, that would really blow. But I'm going to do the fuel test and try to report back.