Topic: Help with loss of power

[kgschlosser]

The HPFP has a solenoid in it.  This solenoid is what does the regulation of fuel pressure. It also removes the pulsing in the pressure caused by the pumping action. so as the cam lobe depresses the pump the solenoid will move one direction and when the lob releases it will move in the opposite.

The solenoid is PWM driven and has a feedback  so the ECM can see if the positioning of the solenoid is roughly the same as the ECM has requested it be. If the solenoid  has an issue you would get a check engine light right away. If the pump was failing mechanically you would have diminished pressure across the board. You aren't seeing a low pressure across the board you are only seeing a problem when a high volume of fuel is needed. This is where the LPFP can cause an issue if it is no good. There is no system that checks what the LPFP is doing. If the pump is able to supply 30PSI of pressure that would allow the car to run properly if cruising about and not pushing the car at all. As soon as the HPFP draws a high enough volume of fuel to cause the pressure to drop on the low pressure side the rail pressure on the high side is going to drop because there is not enough volume to maintain it.


It's pretty cheap to replace the LPFP and it is not that hard to do. There is an access lid under the carpet in the trunk. Just be sure not to bend the float.

You could also have a clogged fuel sock. The sock is the OE fuel filter. It is located at the bottom of the hanger assembly for the LPFP. A common cause of it clogging is a bad charcoal canister. The way the EVAP lines are  arranged on the top of the tank is not ideal. The line runs from the top of the tank and connects to the bottom of the canister. The canister sits directly on top of the tank. There is very little elevation change to the EVAP line. Topping off your gas tank (continuing to pump gas after the pump has clicked off) and also spirited driving (corning at high speeds) causes gas to go up into the EVAP line and it can get into the charcoal filter. Once the charcoal soaks up enough gasoline it will break down into crumbs. The crumbs are small enough to get past the screens in the canister and it ends up in your gas tank. The crumbs are not small enough to get past the fuel sock so they clog it up which limits  the amount of fuel the LPFP is able to suck up.

[KappaSky]

All good info.  Just not looking forward to it as I need to remove the hard top to get the carpet out (without bending it up). Other than that, doesn?t sound too bad.

The days are getting cooler here, so will do it over the winter. I won?t have an update to this thread until spring.

Thanks for all the advice.

[kgschlosser]

no worries m8, I am sure you will get the problem sorted out.

[MattM]

So it might not cause a cel from fuel pressure but would,t the wideband throw the light when it read how lean the mixture was?  I'm guessing it would have to be very lean to cause the belching and stumbling etc..

[kgschlosser]

The way the ECM is programmed is it only check for a lean condition if the engine load  is <= 80% and if the RPM's are below <= 4000. anything above that RPM and no DTC will get set, or if the load is higher then 80% no DTC gets set

There is a lean idle DTC but the engine RPM's must be <= 1120 and the engine load <= 45%. same deal anything above that and no DTC gets set.

This is why you have to be really careful when tuning the LNF because at high RPM if a lean condition is present you will have no indicator that there is a problem and you can burn a hole through a piston or cylinder wall.

Not really a fantastic design, Failure of something like the LPHP or a clogged fuel filter can cause problems only when there is a high demand for fuel and everything would run normal when the demand for fuel is lower. It's right up there with why are the window switches located where they are? Another one is the design of the rear section of the chassis. Why was it designed to allow flex in a corner and when it does it causes the rear tire on the outside of the turn to get a positive camber and a toe out?? We will never have an answer to those questions. I am thinking that to help keep the costs low they used engineers that got their degree and had a 2.0 GPA.

[kgschlosser]

I am hoping that the OP doesn't use the vehicle much until the issue is sorted. and if the vehicle must be used the RPM's get kept below 4000. By keeping the RPM's below 4000 if the problem gets worse a DTC will get set and let the OP know that there is a problem. Going above 4000  has a high probability of causing catastrophic engine damage.

[KappaSky]

No intentions on beating on it! 
As indicated, the weather is starting to turn up here in Canada. Probably have a couple more weeks of decent weather.  The car gets stored as of November 1, so I can start the tear down at that point.
Appreciate all the knowledge that you?ve shared.
Hopefully I can report back good news next spring.

[MattM]

I am hoping that the OP doesn't use the vehicle much until the issue is sorted. and if the vehicle must be used the RPM's get kept below 4000. By keeping the RPM's below 4000 if the problem gets worse a DTC will get set and let the OP know that there is a problem. Going above 4000  has a high probability of causing catastrophic engine damage.

Damn!  I didnt know that about the above 4000 rpms etc.  Hopefully he gets this fixed!!!

[kgschlosser]

It is easier to think of a DTC as a test and the test can have 3 outcomes pass, fail or not taken.

Every DTC has a set of conditions that have to be met before the cars ECM will run checks for that DTC. If the conditions are not met then no DTC will get set if there is a problem. One of those conditions can also be that other DTCs are not set. For the lean condition the list of DTCs that cannot be set is quite long. The conditions are not the same for every DTC, some will have conditions like  on the 3rd cold start of the engine or the fuel tank must be at least 20% full.

[KappaSky]

Have the part. Now to until spring.