Direct injection pump question

[scoobaru88]

I’m leaning towards my direct injection pump is bad, desired pressure is 400psi, and it shows actual pressure is over 2000psi and creeps up to 2700/2800psi until car stalls out. No engine codes. Car just runs horribly and stalls out after idling for 5-10minutes.

Assuming new direct injection pump will fix the issue, but anything else that would cause this issue? Tuner says that the tune is fine. Ran on tune for 3k miles with no issues.

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[Proshop]

It’s plausible but I have only seen people with bad DI injectors. Hopefully some one who has dealt with this issue exactly will chime in.

 

[Joshinator99]

This happens on rare occasion in the Camaro LT1/LT4 world since they are DI-only from the factory. If the commanded DI pressure is significantly lower than actual (per the OP’s post) then installing a new DI pump generally cures it.

 

[scoobaru88]

This happens on rare occasion in the Camaro LT1/LT4 world since they are DI-only from the factory. If the commanded DI pressure is significantly lower than actual (per the OP’s post) then installing a new DI pump generally cures it.

direct injectors were replaced couple weeks ago with no change. Tuner noticed the DI pressure differences, just curious if I’m on the right track.

 

[Joshinator99]

direct injectors were replaced couple weeks ago with no change. Tuner noticed the DI pressure differences, just curious if I’m on the right track.

Yeah that wouldn’t be the injectors in my humble opinion. If you had one injector junk, it simply wouldn’t spike rail pressure beyond what the HPFP could accommodate. It would take virtually every injector locking up to cause rail pressure to spike that high so it’s a very unlikely scenario. I’m going with HPFP on this one…

 

[scoobaru88]

Yeah that wouldn’t be the injectors in my humble opinion. If you had one injector junk, it simply wouldn’t spike rail pressure beyond what the HPFP could accommodate. It would take virtually every injector locking up to cause rail pressure to spike that high so it’s a very unlikely scenario. I’m going with HPFP on this one…

Same. I’ll have to get one ordered.

 

[engineermike]

When 0% di is commanded the rail pressure slowly builds up for a couple of reasons. One, thermal expansion of the fuel in the rail and two, I don’t think the gdi pump can get to true 0% stroke. What I’m saying is it’s normal for gdi pressure to creep up at idle when no di is commanded. There is a de-pressure cycle where it basically commanded gdi blend higher than the tables indicate specifically to relieve this pressure buildup. It’s normal.

 

[Joshinator99]

When 0% di is commanded the rail pressure slowly builds up for a couple of reasons. One, thermal expansion of the fuel in the rail and two, I don’t think the gdi pump can get to true 0% stroke. What I’m saying is it’s normal for gdi pressure to creep up at idle when no di is commanded. There is a de-pressure cycle where it basically commanded gdi blend higher than the tables indicate specifically to relieve this pressure buildup. It’s normal.

While I don’t disagree, there’s a huge difference between “400 psi commanded” and “2700/2800 psi actual” and that’s definitely not normal IMO.

 

[scoobaru88]

When 0% di is commanded the rail pressure slowly builds up for a couple of reasons. One, thermal expansion of the fuel in the rail and two, I don’t think the gdi pump can get to true 0% stroke. What I’m saying is it’s normal for gdi pressure to creep up at idle when no di is commanded. There is a de-pressure cycle where it basically commanded gdi blend higher than the tables indicate specifically to relieve this pressure buildup. It’s normal.

I could see it creeping up some from 400psi but up to high 2k seems a bit much?

 

[MrMike]

Some paranoia here, but I had a 335 before the Stang, and I would immediately swap the HPFP in this scenario just based on that experience.

 

[Cory S]

Most independent DI systems operate between 1900-2800psi. Do these hybrid systems on the Gen3’s run that much less psi???????

 

[engineermike]

Most independent DI systems operate between 1900-2800psi. Do these hybrid systems on the Gen3’s run that much less psi???????

The commanded pressure varies over a wide range as a function of rpm and fuel flow. Max on most gen3’s is 2900 with a limit of 3000, though I did run across a stock cal that commanded 3000. It does run around 400 at idle. I run mine up to 3400 because my pump is bigger than my injectors.

I’m not convinced the pump is the culprit. The pressure is always being controlled by the pcm. If it goes above command, the pcm reduces the pump duty cycle. If it goes too high then it will turn on the gdi injectors to bring it back down. It would take a lot more logging data for me to be convinced.

 

[Proshop]

Most independent DI systems operate between 1900-2800psi. Do these hybrid systems on the Gen3’s run that much less psi???????

Cory I checked my logs and it runs like you stated in the 2k range.

 

[scoobaru88]

Cory I checked my logs and it runs like you stated in the 2k range.

At idle it is 2k psi as well?

I attached screenshot of what forscan shows. This is at idle, it slowly creeps up and once it hits around 2700psi the car starts hunting and eventually stalls out.

 

[Proshop]

At idle it is 2k psi as well?

I attached screenshot of what forscan shows. This is at idle, it slowly creeps up and once it hits around 2700psi the car starts hunting and eventually stalls out.

I don’t have my laptop currently but yes that sounds about what it was.

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