Bad CP3

[catman3126]

So I'm working on a low power issues with a 02 LB7, connect efi scanner and in a matter of seconds I can see that rail pressure is the problem, as soon as I begin to accelerate I can see the desired is 15k+ and actual is staying down around 4K cruising up the freeway at 70 which takes forever to get too. It will run 6-7 k and desired will be 18-20K so I know this is the issue with low power. When I get home I use DVT and run the rail pressure up to 160mpa and the desired stays at 4.5k at idle, but when I rev the engine to 2500 rpm or above it will climb to 16-17k actual while still calling for 23k with DVT. My thoughts are the cp3 is shot. 170K miles, been doing this for 40K the guy said and just seems to be getting worse. the bad thing is he took it to two sdifferent shops and they sold him a new set of injectors once and another place put a S366 on it trying to remedy this problem. sounds like someone doesnt know how to use a scanner. anyway. I kinda ruled out a relief valve issue due to the fact that it will climb up to 17K with no load free reving it. and when driving with a light load it will never even break 8K rail pressure. also i know the sensor is right because the main io=njection pulse is going up to 2900us which if the pressure was actually there and just not seeing the pressure from the sensor this thing would be a runner. was just going to do a bottle test if I get to the hose to do it. let me know what you think. pretty certain I'm on the right track. thanks.

 

[DAVe3283]

Of course, we are assuming you've changed the fuel filter.

Yeah, a CP3 is likely here, but it could still be the relief valve. I'd do the bottle test before swapping the CP3 to be safe.

 

[catman3126]

Yes fuel filter is new and like the guy said he has changed the filter several times over the years and it has never made this issue better. Usually when I have seen the filter plugged the rail pressure will start to ramp up and as the pulse ramps up and the pump requires more fuel the pressure starts dropping. This issue the rail pressure never even starts ramping up and falling back down.

 

[Harbin_22]

If you look at a pulse table, you will see why it is at 2900 pulse. Look at the bottom left of the table, when pressure drops, pulse increases to try to compensate for the lost rp.

But I would try a bottle test and if it is good, maybe a return rate test from the pump alone before replacing the pump

 

[catman3126]

Yep I understood that part, Low rail pressure and high throttle position= high pulse. getting down in that 3900 area if it got much lower.

any good write up on the pump return rate test? Thanks

 

[NC-smokinlmm]

Could have an obstruction on the fuel supply line. Reving at idle will not demand the fuel load that actual driving will so it would probaly beable to get up 17k with an obstruction but not under load. I woud attach a seperate fuel tank (from a small gas can filled with diesel) to the supply line under the hood and see what happens before I did anything else...

 

[catman3126]

Could have an obstruction on the fuel supply line. Reving at idle will not demand the fuel load that actual driving will so it would probaly beable to get up 17k with an obstruction but not under load. I woud attach a seperate fuel tank (from a small gas can filled with diesel) to the supply line under the hood and see what happens before I did anything else...

I agree.

 

[catman3126]

So I pulled the line of the banjo bolt going to the return that connects the injector, rail and cp3 return line that the only one flowing fuel at idle was the cp3 and in 10 seconds time it would have filled a beer can. I know this should be done cranking but as soon as it was cranking the fuel started moving I had a clear hose into a bucket. And it was a steady 1/4 inch stream at idle. There was almost none come from the injectors and not comin throught the relief valve for the rail. So looks like it's time for a new cp3

 

[catman3126]

Yep CP3 was bad allgood now.