I have this ghost issue I’d like some advice/suggestions/ideas on. Most of you know already but...04 gto, 5.3, 7875 turbo

fuel system:
pump 93
2 aeromotive 340’s in the tank. One boost activated
stock 3/8 feed
5/16 Teflon return on the stock rails, on the pressure port but drilled out
custom 1.5 liter bucket
52psi at idle
fuel line is not run close to the exhaust at all.
return dumps into the bucket a a fairly low position close to the pump pickups (I have an idea on this)

so here’s the issue. After cruising a while, stop and go traffic, a good bit of idling and slow speed driving, it I smash on it, it starts to go rich (or ideal should I say) then leans outs to 13-14:1. This is at any boost level, even 4-5 psi on the gate. Keep on mine I can run the car the next day, afr is fine, fuel level does not matter.

I tried zeroing out the boost power enrichment and using just power enrichment. no effect.
I zeroed out the pe and tuned the ve table to desired afr under boost. No effect.
I reflashed the ecm with more fuel. No effect.
I thought it was getting pressure locked so I loosened the fuel cap, no effect
I have forced the 2nd pump to run to be sure it’s on. No effect

the only two things that cures it is letting it sit for a long while or adding fuel to it. I was at about 6 gallons fuel level, I added 6 more gallons while letting the car idle. Immediately made a couple passes, no more lean out.

my thoughts are:
1) the return being close to the pump is constantly cycling almost the same fuel and it’s getting hot?
2) the return is causing it to aerate the fuel and cause the pumps to pick up air/bubbly fuel
or
3) it’s just simply heating up the fuel and well....I dunno. If it was vapor locking, wouldn’t it not run? Or I’d see issues at cruise?

Maybe running a 340 pump is too large to circulate the fuel all the time? I could put a stock pump back in?
or turn the fuel pressure down to like 40-45 at cruise?

ideas?

 

Fuel will heat up with the bigger pumps. Do you datalog fuel temp? I had a similar issue using two 450s and watch temp go up on fuel by 30 to 40 *. Started pwm on fuel pump and issue was gone by holding temp down. Don't know if this your problem just throwing it out there for you

 

I don’t have any kind of temp sensor for the fuel. But say it is heating up....how would that cause it to lean out? Just wondering.

 

does it have a intake air temp correction table. ?

 

Maybe I missed it, but what's the FP doing when this happens, is it rising. Can you read the voltage at the pumps. If the wiring is on the small side, it can heat up and create further resistance.

 

^^^This^^^ FP likely not keeping up. The big question, why? FP reg setting changing with heat? Voltage dropping at pumps?

 

It does but its zeroed out...iat's are usually close to 105 when it happens....btw.....if I add fuel to the tank, problem goes away....my thought it the fresh fuel is either 1) cooler, therefore cooling it off or 2) getting rid of the aeration

 

I dont have a way of checking the fuel pressure right now. I may add a sensor....my guess is that it is dropping, my commanded AFR stays the same (11.31) whether the problem is happening or not. I ruled out the issue to NOT BE in the tune.

 

You can try a temp gun on the tank to crudely try to keep track of fuel temps , you could also be heat soaking the iat sensor . If using hpt there's a table for calibrating that , I'm using an iat from a regal in the evap solenoid position and had to tweak that quite a bit to maintain consistent a/f ratios at various temps OL SD . Driving around on a single 340 shouldn't be a problem, I'm on a single 450 as are many others with no issues. The adding of fuel could have been the fix , or the fact that didn't shut it off - which heat soaks the most . Hope you get it figured out

 

I did pull over and look at my base fuel pressure and its not changing. under power.....I cant say 100% but i'm pretty sure its dropping.

so, i've always run one 340 on the stock wiring....never an issue and kept up with things to 10-12psi. This never happened before I did a return system. Also, I ran 10 gauge wire to the secondary pump, activated by a relay. Theres no way that even if I had a voltage drop....that two pumps (one pump is definitely going to have adequate voltage becuase of the stand alone wiring) couldnt keep up with a measly 4-5 psi at 4500rpm. keep that in mind....this is happening at really low boost.

 

Sorry, I type slow. Lots of new info since I started Lol

 

good idea on the temp gun.

I plan on pulling the tank and changing how the return shoots into the bucket. I saw a radiaum bucket that shoots return fuel at the top of the bucket but it shoots it to the side to create a swirl effect....eliminating aerated fuel...thats what they claim anyways...


look what it says below the 4th picture


http://www.radiumauto.com/MPFST-Mult...ank-P1565.aspx

 

That might help although your problem does seem to have a temperature factor . Worth a try unless it's very expensive

 

I saw a similar issue and after alot of dicking around I changed the way they had the regulator and bam fixed. It had the regulator on the front of the driver's rail. The supply hooked to one side of the regulator and the rail hooked to the other. So the rails didn't get any flow except what was going through the injector. They would get super hot and the regulator would be alot cooler. I moved the supply to the back of the rails with a y and teed the regulator and no more issues. It did have a high ram so I've heard by alot of internet gurus the aluminum intake makes it worse because of heat soak. I didn't think the temp with 58 psi would really make that big of a difference but it did.

 

My buddy and I had fuel pressure issues. I had to remove the sock from my fuel pump with a 525. Don’t think that’s your issue cause you say it’s fine when running at first.

my buddy has a 3xx pump and it had such bad reviews about heat and electricity it draws. He made 450 on it before tuner said it had to go. We swapped to a 450 and his relay wouldn’t get hot anymore and it fixed his issues. Those 3xx pumps just no good IMO. Run hot.

I personally love having my fuel pressure gauge in the car. I would’ve sent car to tuner thinking tune related and chased it thinking not fuel pressure.

 

Thats exactly how I have my regulator now. Maybe I need to rethink how i have it.....I have an extra set of rails i could modify.

 

IDC going way up when problem occurs? This would validate pressure drop. If pumps keeping up with volume and pressure, then reg must be an issue.

 

The supply hooked to one side of the regulator and the rail hooked to the other.
Bass ackwards.
This: I moved the supply to the back of the rails with a y and teed the regulator and no more issues.
"and teed the regulator".
I'm assuming "teed" means the ft of rails into the 2 ports on the reg, then the return out of the bottom. Y/N?

 

the duty cycle isn’t going up unless I add more fuel in the ve. I’m not sure how or why it would go up.....unless I had a self learning ecm. I could be wrong tho....

 

Sorry, wasn't thinking about the ECM your running.