C7&7

So...back in December my car starting making a terrible vibration type noise from under the intake manifold and it turned out being the stock LT1 high pressure fuel pump that took a ****. Replaced it with the LT4 fuel pump and just last week the car started making the same noise only worse this time. Car wouldn't idle, through check engine codes and of course the pump basically sheered itself off the the factory mounting plate and was not supplying fuel properly of course.

So...the car is boosted and cammed with the 32% larger fuel lobe. I am starting to think maybe the fuel lobe could be out of spec or possibly too oversized? I am kicking around the idea of pulling the cam and having a look and maybe just going with the z06 fuel lobe instead of the 32% larger lobe.

Anyone else having issues??? It is a cam that my tuner has put in multiple cars.

Elite275

Someone else had this exact same issue shearing it off...Higgs maybe?

Higgs Boson

yes the LT4 sheared off with a lash cap and stock lobe. now stock lobe, LT4 pump and no lash cap, no problems.

C7&7

It sheared off the mounting plate basically? Not where it attaches to the block but where the pump attaches to the factory plate? So you were running the lt4 pump with lash and a factory lobe? Now you're running the lt4 pump and factory lt1 lobe or lt4 lobe?

Higgs Boson

LT4 pump, LT1 lobe, lash cap = sheared
no lash cap = all good

LT4 pump has a shorter throw than the LT1....

C7&7

oh damn... that explains why the lt4 pump went so quick.

im not sure if my setup is lash capped to be honest.

Higgs Boson

well if it was then it's probably in your oil pan now!

C7&7

C7BB

No... We don't have lash caps.... Only LT4 pump.

WKMCD

I had the stock pump go bad and replaced it with another stock LT1 pump. I run an E-force and it works fine.

Higgs Boson

do you have a bigger cam lobe?

C7&7

Yea he does..and the LT4 pump now. His setup is virtually identical to mine except he hasn't seen this issue.

I am just baffled by it because there are tons of cars our there with an oversized fuel lobe not destroying fuel pumps....

I am just gonna change the cam it go back with the normal fuel lobe. Assuming I will have enough fuel with the LT4 pump not overdriven. Might do a DOD delete cam while Im in there.

C7BB

I would say it's an wet sump/dry sump issue... But Higgs' car is a wet sump car too. Great mystery for sure.

C7&7

Hmmm....

RpeterK

I have a stock pump that I purchased from Theta a long time back when he swapped his out. I bought this to work with in an effort to build a higher volume pump but decided against the idea due to the potential leak into the crankcase should there be a seal failure. Anyway I have never looked but there must be a preferred install height to make sure the pump isnt going into a dangerous area of the stroke. where its being almost bottomed. There are variations to parts although they are close but when your pushing things to the max this could be just like a valve spring going into coil bind. I have not installed a pump and only have the one to work with. I guess assumptions have been made that the mounting height of the pump flange on the std versus Z valley cover are the same. I believe I have both and if so I will check. Would make sense that they would be but GM does plenty of things that make NO sense what so ever. Just throwing some thoughts out. Havent had an engine to take apart to completely research things.

bob

555ctsv

I haven't seen the lt1 and lt4 pumps side by side. Is it possible they are the same pump but the lt4 version just has the lower throw to incease pressure? If that is the only difference i think ill stay with my lt1 pump and aftermarket cam. (I had been thinking of upgrading to lt4 hpfp and injectors to run flex fuel)

Higgs Boson

it won't help you.

if I could do it again I would leave it all stock, add the CPR pump and meth and that's it.

if you are NA you can run E85 without changing any parts. Boost and E85....not going to happen without meth anyways so why change anything?

555ctsv

I have an A&A, Cam, meth, headers; so if I wanted to go to flex I would need some more fuel capacity. Maybe just a low pressure pump upgrade nd some lt4 injectors would be enough

Higgs Boson

won't even be close to enough without meth but since you are already running meth, what's the point in dropping all that cash on fuel system parts when you can just turn the meth up instead? not to mention you don't need E85 if you are already running meth.

black_c7

hey Higgs
my car is lash caped and have the 32% lobe, if i drop the hpfp would anything be bad ? what do you think i need t do ?

thanks