Help- Fuel issue

tv’s 03

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Hi All, I was here a long time ago, but it didn’t recognize my user name anymore. Glad to be back.

I did a build on my 03 over the winter and can’t figure out my issue. Car has a Whipple gen 4 2.9. 3.5 upper, stock lower. I took it to the dyno to have a big name tuner tune it. After the initial data log with a start up tune. All looked good. But when we got to the dyno it was cutting out as soon as you went with.

tuner says it’s an issue with the fuel pumps, which are new Walbro improved GT supercar pumps. Modified FPDM, pprv delete, and dash 8 line from tank to stock fuel rail and huge AFCO race filter feeding FIC 1000’s.

tuner says that they don’t like the pulse width modulations for the returnless system. He wants me to spend another $700 to covert it to a “poor man’s return system”. I don’t think I need to do that, as this system is pretty robust. It may need the wire upgrades, but should make it past the initial stab and a dyno tune.

so that’s the backstory. I trying to figure out what’s wrong. Fuel pressure at the rail is dropping under wot. Fuel pressure drop across the injectors show the same exact numbers as fuel rail pressure. It hold 39-40 psi just driving around and drives great. I swapped out my frps for good measure, no change, checked for vacuum at the sensor, good. When I unplug the vacuum line and block it off, car runs exactly the same. It’s seems like the pcm is not recognizing vacuum at all.

could one of my pumps be bad, or is this a pcm issue? Any ideas? I need help
 

01yellercobra

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The GT pumps were designed for a returnless system. It sounds like he's trying to take a shortcut. Did he change the voltage table?

Who installed the pumps? Maybe there's a loose connection that only shows itself at higher pressure. Generally it'll keep getting looser until things stop working altogether. Or maybe it's a bad wire connection to one of the pumps.

I did have a similar experience with AEM 320's. They worked fine under part throttle, but under boost the pressure would drop. I found I read something wrong and they didn't like returnless systems and one of them burned up.
 

tv’s 03

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The GT pumps were designed for a returnless system. It sounds like he's trying to take a shortcut. Did he change the voltage table?

Who installed the pumps? Maybe there's a loose connection that only shows itself at higher pressure. Generally it'll keep getting looser until things stop working altogether. Or maybe it's a bad wire connection to one of the pumps.

I did have a similar experience with AEM 320's. They worked fine under part throttle, but under boost the pressure would drop. I found I read something wrong and they didn't like returnless systems and one of them burned up.
I installed the pumps. I soldered them directly to the positive and negative terminals on the stock hat. I did notice when I pulled them again and did the porch delete that one of them had brown stuff around the wires at the pump
 

tv’s 03

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I installed the pumps. I soldered them directly to the positive and negative terminals on the stock hat. I did notice when I pulled them again and did the porch delete that one of them had brown stuff around the wires at the pump
Pprv not pourch
 

tv’s 03

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Tuner is not willing to work with me, and this is after buying all my major parts from him. He basically is saying listen to him or he won’t help me. Buy more parts or else I won’t help you. I bought the whipple, JLT RAI, Accufab TB, fuel injectors, a SPEC twin disc clutch and a VMP pump booster from him. So I don’t know if he changed the voltage tables or not. I am also wondering if there is something in the tune making the pcm ignore changes in vacuum/boost. It acts like it is seeing 0 vacuum all the time. Never raises presure with boost, never lowers pressure with vacuum
 

01yellercobra

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First thing is I'd do is pull the pumps. I know it sucks but you need to make sure everything is good. Double check the PPRV delete.

Second is tell the tuner to piss off and find another one. There are too many good tuners to have to deal with that crap.

If you're watching pressure drop across the injectors it will never change. It should stay at 40ish psi. If you have a mechanical gauge it should fluctuate with the changing pressure.
 

tv’s 03

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Im watching several PID’s. Not exactly sure how to read it all. For instant I see fuel pump duty cycle. The highest number I seen was .50. I assumed 50%. Then I read you double this number and that is the percentage. So I want to confirm 100%, because that would indicate the pump to me
 

03' White Snake

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First, did you put the GT pumps in a stock hat or aftermarket?

Stock wiring cannot support the draw of GT pumps. You will need to upgrade the wires from the FPDM to each pump, should be 12 GA to each pump. Doing this in a stock hat is difficult to get the wires into the hat and seal them up from leaks.

I ran GT pumps returnless in a modified stock hat for years, no BAP, with a custom dual FPDM harness, -8an line.... made over 600 rwhp without any issues.

I attached the diagram I followed to wire the dual FPDM harness.
 

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olympic

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Im watching several PID’s. Not exactly sure how to read it all. For instant I see fuel pump duty cycle. The highest number I seen was .50. I assumed 50%. Then I read you double this number and that is the percentage. So I want to confirm 100%, because that would indicate the pump to me

Yes you have to double it, 0.50 is 100%. And I agree with 03' White Snake's post above. Stock wiring can not support GT pumps. Probably worth looking into a billet fuel hat as well at this point.
 

01yellercobra

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Do the newer GT pumps draw a lot more power than the old? I only ask because I ran the old style pumps in a stock hat with a stock FPDM and wiring for years with no issues. Well, not 100% stock as I did have the wire upgrade for the FPDM. When I went to buy the upgraded FPDM everyone was out of stock.

I was going to run twin FPDM's in this car, but the cost for that was too with upgraded lines was too close to the return style set up IMO.
 

tv’s 03

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A couple of things:

1. If it was too much current, wouldn’t it have blown the stock 20a fuse? Wondering if I had a bod pumps the whole time.

2. If I used the stock wiring and harness for just one of the pumps and then wired my second FPDM up and just ran the powers wires from it to the second pump would this be ok? I’m thinking I don’t need to upgrade the stock wire if it’s only powering a single pump.

3. I’ve been reading about a secondary circuit that sends the higher powers to the pumps and that there is a relay under the dash near the glove box. Is this true with the 03 cobra? Could that be a problem? I don’t see many having this as an issue on the 03, but I trying to understand it all

4. Any recommendations on a good hat foe a returnless system. They all seem like return setups these days.
 

tv’s 03

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Do the newer GT pumps draw a lot more power than the old? I only ask because I ran the old style pumps in a stock hat with a stock FPDM and wiring for years with no issues. Well, not 100% stock as I did have the wire upgrade for the FPDM. When I went to buy the upgraded FPDM everyone was out of stock.

I was going to run twin FPDM's in this car, but the cost for that was too with upgraded lines was too close to the return style set up IMO.
This is what’s making me think my system should have at least for me through a dyno session and that my issue has been a bad pump the whole time
 

ITSTOCK

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You're on the brink of maxing out those pumps, even if you upgraded the wiring and added a BAP. You do the wiring not only for higher draw, but also to avoid voltage drop. What fuel are you running? You should be around/over 700rwhp on that pulley/18#'s.

Even if his opinion comes across as harsh, listen to your tuner, he is trying to help you make a smart decision.
 

tv’s 03

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You're on the brink of maxing out those pumps, even if you upgraded the wiring and added a BAP. You do the wiring not only for higher draw, but also to avoid voltage drop. What fuel are you running? You should be around/over 700rwhp on that pulley/18#'s.

Even if his opinion comes across as harsh, listen to your tuner, he is trying to help you make a smart decision.
I was only expecting to make just north of 600, maybe 625 on 93 octane. That is what the tuner said it would do. He just wanted me to run a booster on the stock pumps, so I did buy the booster from him. But the stock pumps have over 100,000 miles on them, so I tried to upgrade them to the Walbros and the booster. I had the booster wired directly to the battery then to the FPDM. We thought that since the duty cycle of the pumps would be reduced by the booster, plus the booster being powered by its own wire from the battery, the stock wiring would be ok. I’m concerned I have a bad pump, so I don’t want to go through all the work to convert to a return style just to have to take the tank down again. From all my research the stock wiring might get hot with extended draw, but should at least get through a dyno tune. It doesn’t deliver with or without the booster hooked up.
 

cajun cobra

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Something similar happened to me. Car ran fine under normal load but would stumble bad under hard acceleration or wot and 100% duty cycle. One of the gt pumps had failed. Finding the bad pump was a little challenging I should have just replaced both of them which is what I would suggest. I run dual fpdm's, gt pumps in a fore hat with a direct power feed from the battery. I would also suggest that since you are using the stock fuel hat to make sure you don't have a line that my have kinked. I went down that road with nothing but problems and finally just spent the $ on a fore hat.
 

tv’s 03

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I gave up and installed the Fore LE1 system with dual 450lbs/hr Ti pumps. It’s a deadhead return system. I got it tuned yesterday finally and it made 625 rwhp and 567 rwtq. Thing made 21 psi with the 3.5 pulley and stock lower. Tuner said my stock manifolds and flow master mufflers were the restrictions causing the over boost situation. But he tuned for it and it’s running strong
 

tv’s 03

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Dyno graph…they accidentally printed time vs rpm but he went from just over 2k to 6500
 

01yellercobra

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Nice numbers. Was the boost reading on his gauge or yours? I saw 18psi with the stock logs, but I'm running a standard inlet.
 

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