Checking injector pressure

[spastik monkey]

Ok, so I picked up a Holley 670cfm tbi for cheap. Mounted up just fine, but now the truck seems to have less pep than before, and the only thing left is the fuel pressure. I know how to check pressure at the pump by pulling the fuel filter and hooking a gauge up there, but how do you check the pressure at the injectors?

 

[4X4HIGH]

What engine are we talking about and what injectors are in this 670 TBI? The reason i ask is because if you're trying to just replace a 350 TBI with a larger one it wont work unless you have a chip burned to correct the dwell time of the injectors. If the injectors are larger and the chip remains unchanged then it will have waaay too much fuel and you're lucky if it even runs at all.

 

[spastik monkey]

Well it runs decent now, just seems like it needs tweaking. They are the injectors that holley supplies, I believe 65lbs/hr

 

[4X4HIGH]

Well it runs decent now, just seems like it needs tweaking. They are the injectors that holley supplies, I believe 65lbs/hr

The Holley units have been known to give problems and alot of people opt out of buying them because of that. My suggestion would be to do some data logging and send the file to Brian @ TBIchips and have him look at it. It could be that the slightly larger injectors are going to need a chip burn to optimize the fuel curve (don't cheap out on this as it could very easily cost you an engine).

 

[spastik monkey]

I'm just trying to get it goin for now. The manual says to adjust fuel pressure to 11psi. I think that'll help alot

 

[eagle mark]

Most manuals I have read say 9 to 13 PSI but 99% of cars I have checked come out at 13 PSI

Old holley injectors were very troublesome but the newer ones seem to have releived this problem. Either way you do need to have correct presure and then log data to see where you are...

 

[Thunder]

First to answer your question. You check the FP the same way as a stock unit. At the down stream side (TB) of the fuel filter. Do you have the adjustable FPR? or the style with the brass plug on the top? If the FPR is plugged you remove the plug, ( drill a small hole thread a screw and pull it out) then you will see a allen screw. Turing the screw in raises FP. Out lowers. Holleys like around 11- 12 PSI in a stock 350.
It will take time for the ECM to learn the changes you made. Run it 20 or so miles over varing loads, speed and RPM before making further changes in fp. Then run it again till you got it right.

 

[spastik monkey]

it has an adjustable fpr. so you check the pressure after the fuel filter but before the fpr itself?

 

[4X4HIGH]

it has an adjustable fpr. so you check the pressure after the fuel filter but before the fpr itself?

You can check fuel pressure anywhere between the tank and TBI before the line goes into the TBI.

I personally have one of these...http://marine-performance-parts.com/cfmtechfuelpsiguageadaptorforgmtbi2843505774.aspx and one of these...http://marine-performance-parts.com/015fuelpsiguage.aspx

This makes life a whole lot easier since you install it and leave it there. The only issue is you cannot check pressure while driving but that can be solved by removing the pressure gauge from mounting directly into the fitting and running a length of fuel hose then attaching the gauge to the other end so you can hang it under the wiper arm (temporarily of course) if you need to see what the pressure is while driving.

 

[eagle mark]

it has an adjustable fpr. so you check the pressure after the fuel filter but before the fpr itself?

Yes! Everything higher then where the presure is set will go out the return line.

 

[Thunder]

You should always check the fp after the filter to get a true FP reading.
Checking the fuel pressure Before the filter is a worthless test IMO.

 

[dave w]

After checking the fuel pressure, check the AFR with a WB O2 Tool like http://www.moates.net/product_info.php?cPath=31&products_id=177

dave w