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Guest 1FASTC4

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Guest 1FASTC4

OK, I stepped down to a slightly smaller Cam to bring the power in about 500 RPM earlier (2500). On the slightly bigger cam the car was running great but power didn't really roll on til 3000 RPM's. Everything went back together fine. Here's the problem: Through first gear, the car runs like it's been lit on fire, all the way to the rev limiter at 6800 RPM. It's fast. Second gear is where my problems begin. In second gear and WOT, as soon at it get to 4000 RPM's, the motor leans way out and stumbles bad. I have to get out of it completely to keep it running. As soon as the RPM's come back down, everything is fine. Distributor, spark plugs and wires, MSD digital 6, timing chain, all new. Fuel pump is a Holley. black I can't find any crimped lines in the fuel lines. If it's the fuel pump, why wouldn't it fail in first gear? All I changed was the cam and I added some T&D roller rockers, stiffened the springs a tad.

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corvettech

id start with the basics, what is the fuel pressure and is it holding under a hard load, if thats good you might try checking back pressure at the upstream o2 sensors, maybe the cats got pluged at a bad time, ive seen pluged cats pull some bad voodoo and cause all kinds of odd problems.

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Guest 1FASTC4

id start with the basics, what is the fuel pressure and is it holding under a hard load, if thats good you might try checking back pressure at the upstream o2 sensors, maybe the cats got pluged at a bad time, ive seen pluged cats pull some bad voodoo and cause all kinds of odd problems.

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Definately a fuel problem for sure. We used to have that happen to our drag cars back in the day. Fuel pressure or fuel delivery one of the two.

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Desertdawg

How does it run in 3rd? 4th? ???? Also what does your air intake look like? Sounds like you may have a problem sucking air as you get to speed, maybe a backdraft (duh, can't think of how to word it) where it's not allowing air to flow into your airfilter!

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I'm going to hook a gauge up and check fuel pressure thanks. But why wouldn't fuel pressure drop out in first gear?

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it would be best if you can duplicate the 'lack of power' while in the garage, and having someine sniff the tailpipe.

too bitter/acid= lean

to sweet= rich

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Guest Sidewinder

Put it on a dyno with a wideband. That way your not out one the road flogging it with idiot drivers in the way and you can monitor your readings (air, fuel, spark) in a controlled environment. LPM has a great dyno setup.

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Did you mod the prom to adjust for the change in the cam? You will need to mod the chip as the values have changed. You will need to take it to a tuner on a dyno.

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No cats, no O2 sensors on this motor. No computer, no injectors..... just an old fashioned 383.

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I know you replaced the timing chain, but it might be worth checking timing again.

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id start with the basics, what is the fuel pressure and is it holding under a hard load, if thats good you might try checking back pressure at the upstream o2 sensors, maybe the cats got pluged at a bad time, ive seen pluged cats pull some bad voodoo and cause all kinds of odd problems.

I'm going to hook a gauge up and check fuel pressure thanks. But why wouldn't fuel pressure drop out in first gear?

No cats, no O2 sensors on this motor. No computer, no injectors..... just an old fashioned 383.

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Guest 1FASTC4

OK, you guys are on it! So, the car doesn't go lean in first gear because the bowls start off full. As the bowls get empty due to low fuel pressure, the car leans out. I know it ls leaning out because I have a wideband AFR gauge in the car. So, with this informaiton I put a fuel gauge inline and discovered I have only 5 PSI to the regulator. Unfortunately, the most I could get was 6 PSI so I may still have a problem... dying pump(Holley Black 3 years old)? clogged filter(new)? kinked line(none visible)?

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Final Effort

I say it's fuel volume. disconnect the gas line at the carb and measure the volume of gas the pump is putting out after the filter and pressure regulator.. Compare what volume you got to what your supposed to be getting from that pump.

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OK, you guys are on it! So, the car doesn't go lean in first gear because the bowls start off full. As the bowls get empty due to low fuel pressure, the car leans out. I know it ls leaning out because I have a wideband AFR gauge in the car.

So, with this informaiton I put a fuel gauge inline and discovered I have only 5 PSI to the regulator. Unfortunately, the most I could get was 6 PSI so I may still have a problem... dying pump(Holley Black 3 years old)? clogged filter(new)? kinked line(none visible)?

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Guest 1FASTC4

OK, you guys are on it! So, the car doesn't go lean in first gear because the bowls start off full. As the bowls get empty due to low fuel pressure, the car leans out. I know it ls leaning out because I have a wideband AFR gauge in the car.

So, with this informaiton I put a fuel gauge inline and discovered I have only 5 PSI to the regulator. Unfortunately, the most I could get was 6 PSI so I may still have a problem... dying pump(Holley Black 3 years old)? clogged filter(new)? kinked line(none visible)?

What pressure after the regulator?

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Could be a mal adjusted or sticky float in the carb reservoir. If you start going full throttle from a cruise in 2nd gear, does the lean condition occur in 3rd gear, too?

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Final Effort

Remember don't confuse Psi for volume. Looks to me like it's your fuel delivery system. I got this info from Jegs. What Black pump do you have? #12-815-1 Black Pro Series Electric Fuel PumpsFor street/strip or water race applications # Compatible with alcohol # Preset to 14 psi # Flows 120 gph maintaining 9 psi line pressure # Free-flow capacity of 140 gph # Regulator required # Mounting bracket and relief valve included # The marine pump meets USCG regulations (Holley P/N 510-12-803) The Holley HP 150 delivers 150 GPH at free flow (140 at 7 psi) and is internally regulated at 16 psi to work efficiently with the included 4-7 psi regulator

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Guest 1FASTC4

Could be a mal adjusted or sticky float in the carb reservoir.

If you start going full throttle from a cruise in 2nd gear, does the lean condition occur in 3rd gear, too?

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You can always try a run through 1st and just after it falls flat in 2nd, kill the motor (assume the pump too) and coast to a stop in neutral of course. Pull the carb top and check the level in the bowl. If that bowl is empty, it's a lock that either the pump is faulty under the demands of the load or there is a restriction in the line. Unless you have a full tank, a vacuum in the tank will not react that quickly. While you have the top off, turn on the pump and see how long it take to fill the bowl if it's empty. It should happen quicker than the time it took to empty it. I saw a restriction in a carb inlet one time that was caused by some leaf gathering insect. When the fuel demand was low, it could supply enough, but when the demand went up the pump couldn't supply enough. The carb had not been used for quite some time and that's when the bug dragged in his food supply.

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Glad to hear it was a realatively easy fix!

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Final Effort

I say it's fuel volume. disconnect the gas line at the carb and measure the volume of gas the pump is putting out after the filter and pressure regulator.. Compare what volume you got to what your supposed to be getting from that pump.

Remember don't confuse Psi for volume. Looks to me like it's your fuel delivery system.

I got this info from Jegs.

What Black pump do you have?

#12-815-1 Black Pro Series Electric Fuel PumpsFor street/strip or water race applications

# Compatible with alcohol

# Preset to 14 psi

# Flows 120 gph maintaining 9 psi line pressure

# Free-flow capacity of 140 gph

# Regulator required

# Mounting bracket and relief valve included

# The marine pump meets USCG regulations

(Holley P/N 510-12-803)

The Holley HP 150 delivers 150 GPH at free flow (140 at 7 psi) and is internally regulated at 16 psi to work efficiently with the included 4-7 psi regulator

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Guest 1FASTC4

I say it's fuel volume. disconnect the gas line at the carb and measure the volume of gas the pump is putting out after the filter and pressure regulator.. Compare what volume you got to what your supposed to be getting from that pump.

Remember don't confuse Psi for volume. Looks to me like it's your fuel delivery system.

I got this info from Jegs.

What Black pump do you have?

#12-815-1 Black Pro Series Electric Fuel PumpsFor street/strip or water race applications

# Compatible with alcohol

# Preset to 14 psi

# Flows 120 gph maintaining 9 psi line pressure

# Free-flow capacity of 140 gph

# Regulator required

# Mounting bracket and relief valve included

# The marine pump meets USCG regulations

(Holley P/N 510-12-803)

The Holley HP 150 delivers 150 GPH at free flow (140 at 7 psi) and is internally regulated at 16 psi to work efficiently with the included 4-7 psi regulator

Ok WHAT DO YOU HAVE FOR ME JOHNNY ?

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