[KlrStng]

I hate to get my hopes up, but I have been chasing this problem for so long now, and every potential fix led to worse problems than before. However, I have a feeling I might have found the issue.

First, for those that didn't follow my Kenne Bell install a couple months back, let me go over the issues again.

I installed the supercharger, but they sent the wrong MAF setup (sent the tune for the one they should have sent), so my AF was way too high. I got the new MAF setup and all seemed good.

Then I drove the next morning, and the engine bogged down and sputtered when I gave it gas. The AF gauge shot up when this happened. Once the car was warmed up, no problems. I called KB, and they told me to check plugs and look for a vacuum leak. Between advice from local mechanics and people here, I contacted KB about the tune, and they gave me the typical spiel about the tune works in all the other cars, it should work in yours. I went with that philosophy and started troubleshooting.

First, I changed back to factory plugs. No change.
I regapped the HT0s and put them back in.

Second, I checked for vacuum leaks (with carb cleaner) and didn't find anything.

Third, I bypassed the boost-a-pump vacuum switch. No change.

Now, I started getting an idle problem.. idle would drop too low when coming off throttle, sometimes stalling. I cleaned the throttle body, no change.

KB sent me a richer tune (since AF was going lean), but it only resulted in throwing a rich code, and the bogging and sputtering was still there.

I figured maybe the seal between the supercharger and manifold was not good enough, so I pulled it off, and despite the o-ring they put in now, I used silicone. No change.

Based on the oddball AF I was seeing when the problem hit, the MAF was suspect, so I got a new one from KB. No change.

Now I got serious. I took it to a mechanic and he worked on it for a couple weeks in his spare time. He datalogged a little, and the only thing he could point out was the fuel trims were excessive. This makes sense at our elevation as MAF tables for elevation are conservative and up here we see boosted applications go rich, particularly on cold run.

So we started looking at it from that perspective. When cold, the LTFT was around -18%, pulling a LOT of fuel to attempt to run right. In open loop, LTFT is ignored, but we figured this was a symptom of a rich condition. I even threw 2 more rich codes during cold run, despite being on the original KB tune.

In the mean time, we smoked the engine with a very good smoker. We found a massive vacuum leak in the plenum connected to the back of the supercharger. This was a flaw in the build, and I had to pull the supercharger again to fix it. After fixing it, I smoked it again and had no leaks. The problem actually seemed to get worse. Idle was really getting erratic now, and the bogging was as bad as ever when cold. Now idle was getting rough, something that had never happened before.

So after all this, KB decided to send me a new tuner, an SCT X3 so I can datalog and send them the info. Along with this were 2 new tunes to try. The new tunes have made an improvement, but I wasn't sure why. (It looks like, from the tune, they turned off the cold run, so it is always in closed loop now, except when on WOT. This way the O2 sensors are seeing whatever problem happens when cold and corrects it. I don't know this for sure but I suspect it.)

Today, I datalogged a cold start and run, and sent the data to them to analyze. Shortly after emailing the data, I started looking at it closely. You see, in the past few months I have learned a LOT about how these engines work, and each day I learn more.

A couple weeks ago I heard about a TSB for a problem when coming off a long highway cruise, the engine can stall. The TSB says it's a fuel pump problem, but I talked to people who had the problem and it only happened on the highway. Mine was happening on the highway (stall when push in the clutch at 70 mph), but also the idle was dropping just around town, and occasionally stalling after running hard. Similar issue, but not identical. Using my Aeroforce Interceptor gauge, I watched Fuel Rail Pressure and it stayed pretty much 40 psi, jumping when under boost. However, based on the TSB and the stalling, I wondered if the fuel pump couldn't be the source of the idle problem.

So, where does this leave me right now? Well, I took a close look at this mornings data log, particularly zooming in on the one time it sputtered and bogged when I gave it gas. The new tune seemed to help this problem, but it didn't go away. I attached a screenshot of the graph I was looking at. In blue is RPM, in Green is Throttle position, and in yellow is fuel rail pressure. I was in first gear, and lifted off the throttle, put the car in 2nd, and applied throttle. As I applied throttle, the engine bogged for a short time (.3 seconds maybe) and then took off. On the graph, you see throttle start to go up, rpm is still dropping, and fuel rail pressure drops to about 25 psi. This is all happening when the engine was sputtering and the AF gauge was going up. Then the engine stopped sputtering, rpms went up, and at the same time, fuel rail pressure had gone back up.

From this data, combined with the TSB about stalling when coming off the highway, I am thinking the fuel pump is bad.

Here is the thing: I could run the engine at idle for 20 minutes, but still have the bogging problem for a short time, as if I had to "flush" the engine out by pushing it. This part has never made sense. However, look at it from the fuel pump perspective.. it is able to pump after sitting for a while, but only barely. When the duty cycle increases, it hesitates before providing fuel. After a few bursts of fuel though, it starts functioning better, and the car runs normal. However, when returning to the lower duty cycle for idle, it pumps a little irratically, possibly causing the bouncing idle.

So that is my thinking, and the solution, rather than to replace the factory pump, is just to get the GT500 fuel pump setup. What do you guys think? Am I overanalyzing the problem or do you think I might have finally nailed it? I hate to spend $750 and get my hopes up only to find the problem still exists..

[stlwagon]

You should deep six that pump and the BAP and install the GT500 pumps and be done with it!

[Scrochy]

I agree with the fuel pump issue, plus i like your red squigglies on the data log

[cnsfugate]

For sure. I hope that is the issue but atleast your upgrading the fuel system and totally elminating that possibility as a problem.

Good luck man I know I have followed the soap opera. I hope this is the last problem.

Sure enough you will fix it a week before the 1st snow

[Jimmy Toronto]

I hope that fixes the problem, I have followed this as well .. GOOD LUCK

[jaja6009]

+1 on following this and hope this works. All of this is beyond my troubleshooting abilities. But I really do hope this fixes it.

[Muckerpuck]

And since your looking at the gt500 pump setup and people are chiming in i would ask a question. Ive had a couple of the pump problems in the tsb's, particularly the one were you gas gauge drops off and get a fuel code thrown. It says to replace the pump and senders.

So if i went with a Gt 500 pump setup , i would only need the other ford sender correct. The gt500 pump would be ready to drop in with its sender correct?

The stock setup is pump/sender, then separate sender correct?

[Back@itagain]

Not trying to rain on the parade and I might not have a clear understanding of what is going on but it sounds like the same thing my Whipple (with GT500 pumps) was doing. Hopefully I am wrong but on cold starts mine would buck and sputter. The 1-2 shift was the worst and felt like the blower was winding up and abruptly cutting, winding up and cutting until the rpms got above 2k or so. Once up to operating temps these symptoms were not so obvious but still present. I had to try and maintain my rpms above 2k to avoid the problem. I could hear a pop through the exhaust on the 3-4 shift at times. I even started to think it had to do something with air intake temps since it seemed so sporadic at times. Livernois did my tune and it took them several tries to get it out. Not sure if the tune was a bandaid or the cure but the problem is not nearly as apparent.

[stlwagon]

Originally Posted by Muckerpuck

And since your looking at the gt500 pump setup and people are chiming in i would ask a question. Ive had a couple of the pump problems in the tsb's, particularly the one were you gas gauge drops off and get a fuel code thrown. It says to replace the pump and senders.

So if i went with a Gt 500 pump setup , i would only need the other ford sender correct. The gt500 pump would be ready to drop in with its sender correct?

The stock setup is pump/sender, then separate sender correct?

Correct... The GT500 setup is plug and play. It comes with the new FPDM that you plug into the existing harness.

[Preston951]

I sure hope you found the problem!

Here's a GT500 pump for a little less than $750... This is the best price I could find...

Stage 3 Motorsports 2005-09 Mustang GT Dual Fuel Pump Upgrade Kit

[1035GT]

Very helpful thread. I plan on getting a KB so this is probably going to be useful. I hope changing those pumps work.

[10/05gt]

Looks like your on the right track with the fuel pressure but if I might add. Did the stock fuel pump exhibit these problems before the SC and BAP install? If not then its a big coincidence that it started now.

Are 39lb injectors part of this package?

My former engine set-up was a Novi 2200 and 9/10 psi. I ran the stock pump and a BAP on the stock rails and 39lb injectors with absolutely no problems.

The one thing that was different though was the BAP was set to full rich and I didn't have the boost reference signal connected.

I honestly don't think you need the GT500 pumps for this SC set-up unless you got a whole bunch more going on in the motor.

[KlrStng]

Originally Posted by 10/05gt

Looks like your on the right track with the fuel pressure but if I might add. Did the stock fuel pump exhibit these problems before the SC and BAP install? If not then its a big coincidence that it started now.

Are 39lb injectors part of this package?

My former engine set-up was a Novi 2200 and 9/10 psi. I ran the stock pump and a BAP on the stock rails and 39lb injectors with absolutely no problems.

The one thing that was different though was the BAP was set to full rich and I didn't have the boost reference signal connected.

I honestly don't think you need the GT500 pumps for this SC set-up unless you got a whole bunch more going on in the motor.

Yes, the setup came with 39 lb injectors, and the BAP is more than sufficient to cover the needs of an 8-9 psi setup with the stock pump. However, if the fuel pump is indeed bad, which is what I am suspecting, I don't see a reason to just replace the stock GT pump when I can use this as an opportunity to upgrade to the GT500 dual pump setup and eliminate the BAP, and any potential problems associated with running the stock pump at the higher duty cycle. I just don't want to spend the $750 and find that I gained nothing but a more solid fuel delivery system.

For the record, there are other KB setups here in town that run the same basic tune and work fine. This is not an issue with the supercharger, it makes boost just fine, and when fuel is getting to where it needs to be, it makes power just fine. I have always been looking for a mechanical fix, and this is the closest I have been.

The problem was NOT present before I installed the supercharger. The problem, however, is not in fuel capacity, it never has a problem at WOT. The problem is in the other end, when it is supposed to be delivering smaller amounts of fuel. On a return system, the pump would just be running and excess fuel returned to the tank, but on the returnless, it is dependent on the fuel pump driver being able to regulate the demand perfectly accurately, as well as the pump to be able to cycle on and off precisely every time.

The increased demands and stress from the BAP could have been what triggered the glitches in the pump, or perhaps it's the FPDM. Either way, a replaced pump, and a second pump with it's own FPDM would correct the problem.

When you throw into the mix the fact that the longer the vehicle sits without putting a load on the engine, the worse it runs when you do finally put a load on the engine, you can start to rule out things. If the problem was in the cold run part of the tune, then starting the car and letting it warm up to temp in the driveway would result in it running fine, but that does not happen. I always associated the problem with the cold run, because the engine is cold when the problem occurs. However, the problem will stop under the right conditions before it is fully warmed up. Also, the problem exists when we force closed loop on the computer, although it is far less pronounced (probably because the feedback from the O2 sensors is allowing it to correct the problem where in open loop it just happened and there was no feedback to allow the pcm to adjust). On the other hand, if I let the car sit for 3 days then drive, the problem was incredibly worse, but a few cycles of heavy throttle allowed it to go away and run right.

The other factor is that the problem is getting worse, occasionally showing similar (although far less pronounced) symptoms when fully warmed up and having been run for a long period of time already. The idle issue is also causing a problem.

I could spend the next few weeks datalogging to see if I get the same results over and over, or I can just bite the bullet and order the pump and hope it fixes the problem.

I still think the tune is a little rich on the cold run, which can be corrected with tuning, but I strongly believe the fuel delivery is the issue. The stumbling/bogging/popping has always sounded like the engine was starved for fuel. Until I actually logged the fuel pressure with a laptop, I never saw the subtle and very rapid change that is reflected in the above graph. I have been over so many things on this engine, I had already convinced myself that either fuel delivery or throttle body was the root cause of the problems, and this only adds to that hunch.

Two other factors come into play here though: It looks like I need to start back at square one on my rear end yet again as I have terrible noise at the neutral throttle point coming from the rear end. I have been into it 4 times and spent a lot of money on parts and labor (through 2 sets of gears, my choice there), and want it to just be fixed. I am taking the car to another shop to find someone who is best qualified in this town to set up the rear end and by the time it is done I expect to spend another $600 there. So it hurts a little to spend $750 on a fuel pump, and I need to be more convinced it will fix the problem. (plus I want some GTA mufflers, and then I am talking some real money again).
The second factor is the upcoming International Mustang Meet here in town. It's the biggest event of the year for around here, and included in the show is the use of a dyno (for pulls only, no tuning), and drag racing at the track, both of which I am signed up for and want to have the car running right for. I have less than 2 weeks, so i have to decide fast if I will continue with the datalogging and tuning or shoot for the potential hardware fix. If I can get the core problem sorted out, I have a friend here that has some KB tunes he wants me to try.

I am going to sleep on it and decide in the morning what to do. Hopefully tomorrow, the tuner at KB will have his opinion ready for me, and i can throw that into the decision process.

[sqidd]

Have you tried eliminatig the BAP all together?

[KlrStng]

Originally Posted by sqidd

Have you tried eliminatig the BAP all together?

No, but there are a couple things there that affect that decision:

First, the BAP was originally set up with the vacuum switch, and when I meter voltage feeding the FPDM, it is ~13v when the switch is off. Since the problem occurs when I am out of boost, it occurs when the BAP is only passing along the stock voltage, not actually doing anything.

Second, even with the vacuum switch bypassed, I read a steady 17.2 volts at the FPDM, and there is no change in the problem.

Third, the BAP is basically a voltage transformer. It is not doing anything with the pulsing of the pump or controlling its duty cycle, it just gives more input voltage to the pump driver module, which results in a higher output on the driver module. While it would be possible that the BAP is fluctuating in voltage, I would think it would show up as a huge fluctuation in the duty cycle that the OBD2 port shows, and that is not the case.

I could be wrong, but I am somewhat confident the BAP is not the issue. Of course, my track record on successfully fixing this is pretty poor though, so I will keep it in mind. Thanks!