Builds 4508 - Ultra4 Racetruck Build (1 Viewer)

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Could you have a piece of debris in the lines or crap in the injectors? How is your regulator ran? Regulator allowing too much fuel to return?
 
Could you have a piece of debris in the lines or crap in the injectors? How is your regulator ran? Regulator allowing too much fuel to return?

I blew all the lines out with compressed air and they seemed clear, and unless all the injectors are clogged and only at high rpm I don't think it's that. Right now it's just the stock regulator.

I've essentially narrowed it to either the pump or the regulator. Interestingly, I looked at reviews for the pump I have and there was one guy who said that after 3 months the pump wouldn't hold pressure at WOT and described the exact symptoms I have which makes me think it's the pump. I checked the lines, I opened the tank and ran it to make sure it wasn't pulling a vacuum, I bypassed the tank pickup and put the hose right into the fuel, I tried it with and without the filter, I disconnected all the lines from the engine and blew them out both ways, etc. So either the regulator isn't fully opening or the pump can't keep the pressure up when she's sucking a lot of fuel. I'm gonna try to get a pressure gauge tomorrow and test where it's losing pressure, but based on the review describing to a tee what seems to be happening to me, I feel like it's the pump.
 
what sized brand pump are you running?

A summit one, 45psi and like 400L/hr or something. Every thing worked without issue at trail hero and in Moab. This exact same setup worked fine and the only thing different is I moved the fuel cell around.
 
Could it be the fuel pump sucking the rubber fuel supply line shut under high demand?
 
Could it be the fuel pump sucking the rubber fuel supply line shut under high demand?

I don't think so, the only rubber sections is a 1" piece immediately after the pump and then the actual pickup inside the tank, but to eliminate the pickup idea I took the stainless line coming off the tank and just submerged it into the tank itself and still had the issue happening.

I'm going to go out right now and try moving the pump, right now the pump is above the tank (which used to be about level with the tank) and the relation of the fuel cell to the pump is literally the only thing that changed within the fuel system itself. I find it hard to believe that would do this, but I read a bunch of posts last night that pumps usually want to push gas and want to have a siphon/positive pressure head going into the pump and not make the pump suck if possible. Hopefully it's as simple as that.
 
So..... I'm an idiot. It's the rev limiter.

I got a fuel pressure tester and the pump is totally fine throughout the whole range. My dad suggested it was maybe the rev limiter actually, or maybe the tranny being weird since the tranny cooler wasn't hooked up. I hooked up the cooler and took my dad for a drive (which I guess was his first time riding in it since I took it!) and he said it totally sounded like the rev limiter which I agree with. If you give it 80 or 90% throttle it's totally fine and up shifts and everything. If you floor it it seems to hold gear and hit the rev limiter which is weird...

It's never done this before, but my dad is very certain it's the rev limiter kicking in and it does sound like it now in retrospect plus you can definitely feel it hit the power band and then rev past it. It seems to be that I thought a safety feature was something broken in the fuel system. We think there might be an issue with the tranny since it won't up shift, so I'll just have to drive it accordingly. I wouldn't be surprised at all if the tranny has issues, lord knows I've beat the s*** out of it pushing the 35s and 40s racing and in the sand in Moab/Sand Hollow.

So yea..... the fuel system and engine seems to be totally fine.
 
I would do one of the shift kits on the transmission it really helps firm up an old worn out transmission and is only $130 and a couple hours of labor.

So..... I'm an idiot. It's the rev limiter.

I got a fuel pressure tester and the pump is totally fine throughout the whole range. My dad suggested it was maybe the rev limiter actually, or maybe the tranny being weird since the tranny cooler wasn't hooked up. I hooked up the cooler and took my dad for a drive (which I guess was his first time riding in it since I took it!) and he said it totally sounded like the rev limiter which I agree with. If you give it 80 or 90% throttle it's totally fine and up shifts and everything. If you floor it it seems to hold gear and hit the rev limiter which is weird...

It's never done this before, but my dad is very certain it's the rev limiter kicking in and it does sound like it now in retrospect plus you can definitely feel it hit the power band and then rev past it. It seems to be that I thought a safety feature was something broken in the fuel system. We think there might be an issue with the tranny since it won't up shift, so I'll just have to drive it accordingly. I wouldn't be surprised at all if the tranny has issues, lord knows I've beat the s*** out of it pushing the 35s and 40s racing and in the sand in Moab/Sand Hollow.

So yea..... the fuel system and engine seems to be totally fine.
 
I've been on a pit crew for a 4400 series car the last 4 years. Team 602.And have helped with a 4500 car the last 2 years. Team 4544. Every year is a new challenge. It's a lot of fun out there. This year I'll be there on Monday the 5th. I'll be driving my beat up green and grey 80 around and at pit 2. I'll keep an eye out for you and say hi. Good luck!
 
I would do one of the shift kits on the transmission it really helps firm up an old worn out transmission and is only $130 and a couple hours of labor.

That's a good idea, I'll look into that after KOH. One of my buddies also suggested that if there's a shift capable it might be out of adjustment (idk if 80s have that, but I know the shifter seems to have a lot of play itself so will see about tightening everything related to the tranny).

I've been on a pit crew for a 4400 series car the last 4 years. Team 602.And have helped with a 4500 car the last 2 years. Team 4544. Every year is a new challenge. It's a lot of fun out there. This year I'll be there on Monday the 5th. I'll be driving my beat up green and grey 80 around and at pit 2. I'll keep an eye out for you and say hi. Good luck!

Thanks! I'll keep an eye out for you too and hopefully we'll run into each other!

throwing a cheap tach on it might not be a bad idea either if you dont have the factory gauges in it

My thoughts exactly! If I can get a tach and tranny and coolant temperatures then I'll be super stoked. Probably just buy some gauges at O'reilly.
 
That's a good idea, I'll look into that after KOH. One of my buddies also suggested that if there's a shift capable it might be out of adjustment (idk if 80s have that, but I know the shifter seems to have a lot of play itself so will see about tightening everything related to the tranny).

80s have it, some people call it a throttle cable. follow your accelerator cable up to the motor and the throttle cable will be there. I found a quick guide on how to adjust it here on mud somewhere.
 
Sniv, how are you fairing now? Is it buttoned up enough to safely, semi-reliably race? Hoping to hear some great stories starting next week!
 
Been wanting to post bit havent had any time or even taken any pictures. Right now I'm about 10 minutes from leaving and the truck is all loaded up! Hopefully can post some pictures from Hammertown, the truck has had a lot of detail work happen from making a dash to fuel stuff to a spare tire carrier. I race a week from Thursday and hopefully at Hammertown tomorrow night. If the internet there is decent ill put some photos up!
 
Currently showing DNF like many many others today, but still excited for you to get to compete and can’t wait to hear some great stories!
 

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