Fuel Pressure Woes...

[3X00-Modified]

Maybe a few more minds on this topic will help...

I have a Caspers AFPR on my fuel rail right now, I'm running the trailblazer Injectors which are 28# per/hr at 61PSI... I have my pump set for 62PSI at WOT, so all is good there...

Now I have two issues that have to be related and I'm not sure of the source.

1) Hard starting. Never had this issue before up until a few weeks ago, always started quickly, even if it was followed by stalling due to the large cam, but it would fire quick before.

2) Large pressure drop when nitrous fuel solenoid engages. This is where I noticed it the most and it worry's me... its enough of a drop for long enough to have the a/f ratio on my wideband hit 14-16:1 for one line in my log... Yeah short but its still there.

it drops from 63PSI down to about 25 for what seems a split second, but you can feel it.

I have a gauge on my car right now so I can see it driving, I have NO issues at WOT n/a or even just doing a key on prime test... the pressure goes up and stays up there it does not drop of quickly. Yeah it will bleed back down to 0 over 3-4 hours but that can't be my issue.

I just tested and when I start it jumps to 60 and stays there while cranking... so its not the similar symptom of no pressure while cranking because the pump primed and the regulator didn't hold it.

Now the nitrous setup, its a line that taps off of my pressure valve on my rail, and by the coil pack and down to a solenoid that's on the other side of the brakes, then there is a 18" line to the nozzle that's in the TB spacer. I'm assuming this drop in pressure is due to filling the long source line of any air pockets, and also filling the 18" up to the jet in the nozzle... Back to back engagemnt of the fuel solenoid does not produce the same drop, its only the first one say ever 5 min or something, so I'm assuming by the the 18" line is sucked dry from the vaccum of the motor since thats after the solenoid.

Either way the only thing that comes to my mind is fuel FLOW being an issue... I have a 255lph walbro HP pump, and I had to modify my bucket to make it fit...

PIC






The pump has direct access to the bottom of the tank so its not stuck in the factory bucket that could be drained quickly... I'm thinking and hoping, the rubber line I used was a little long, you need to compress the springs on these pickups to get them down and in, and I'm HOPING TO GOD that the rubber line just got softer and kinked a little and is restricting flow...

I've also purchased a new fuel filter, since I did change that when I did my tank but it was a god who knows how old filter I had lying around...

The hard starts did not start happening right after I installed this pump, it actually fired REALLY quick the first time after setting this all in, and I figured it would crank more the since the line was empty.

I want to say this all started a few weeks after I did the pump... so thats why I'm thinking something changed in there due to that excess compression and I hope its nothing I can't fix quickly.

[wicked-irocz]

I was actually concerned about that when I saw the picture and although I'm sure its not your issue, I would replace any worm gear clamps with high pressure ones. That pump should easily be up to the task of supporting that combo. I wouldn't worry about the nitrous line stuff until you figure out the starting issue. Does it start right off if you let the pump prime then try starting it?

[3X00-Modified]

Does it start right off if you let the pump prime then try starting it?

Not really... Its odd... I've let it prime twice some times and its still an odd or hard start. Not as bad as if I were to just jump in and turn key... but still not as quick as it should be. I'm starting to wonder if maybe my tune could be off in a way to delay the start, But I haven't really changed anything. When the car is warm it fires right off no problem.

I doubt the clamps are an issue since it holds pressure fine, once I shut the key off it will sit at 60 for a while, if one of the clamps were loose it would bleed down quickly. I'm almost feeling that there is some sort of kink in the system or maybe my filter is plugged with something that was in it that I didn't know about... I have no clue.

Right now my plan of action is to drop the tank on sunday morning to inspect that rubber line when the pickup is compressed down, and also do the filter at the same time... hopefully the combination of the two will solve all the issues.

[woody90gtz]

Wow, that is hella different than the Walbro that came with my 91.

This is a strange problem. With 60psi you would think it would lite very easily, cold or hot.

[3X00-Modified]

Woody that's the entire pickup, not just the pump. The pump is just a small cylinder.

[wicked-irocz]

when I said "concerned about that when I saw the picture" I meant in the thread and the hose.

[3X00-Modified]

Yeah now that I re-read your post it makes more sense

Well sure enough the hose was too long... I should have measured the pump in its installed length, and made the hose to fit that... I fit it fully extended and when I put it in I was like OK its compressing... I left it that way for a day or so and it didn't kink, BUT it hadn't had any fuel run through it to soften it up.

Well here are the pics...

I'll be replacing the line with a shorter length, and I'll do the better fuel pressure clamps too.



Not only did it kink, but it split as well, thats why I need to replace the line.

[wicked-irocz]

I'm guessing the pressure build up enough to burst the line.

[Cliff8928]

Usually if it's fuel injection line it will hold quite a bit of pressure (at least 100 PSI).

You may even have been better using a loop of line so it could flex up and down easier. But the shorter length should work well too.

On another note, could you actually use an older (93?) fuel sending unit that has the fixed length hose and exposed pump?

[wicked-irocz]

I blew the fuel injection hose on my car.

[3X00-Modified]

Usually if it's fuel injection line it will hold quite a bit of pressure (at least 100 PSI).

You may even have been better using a loop of line so it could flex up and down easier. But the shorter length should work well too.

On another note, could you actually use an older (93?) fuel sending unit that has the fixed length hose and exposed pump?

Inlets are different on the tank, I was going to do that on my old setup but couldn't get it to fit. I was thinking a loop of hose, but 3/8 hose is very thick and does not loop nicely...

I think the loop being un-reinforced would have eventually turned into a kink too. The shorter line works great so far, my quick starting is back and there is no more dip when I engage the nitrous fuel solenoid.

[MY91GT(Z)]

nice to see that it worked out and hope to see this car turn out some nice times at ne fest