Why Can't I Lower the A/F?

[MiataVOL]

After the engine reaches operating temperature, the J&S lights-up at anything more than moderate (1/2 throttle) acceleration at 2500 – 3500 rpm when coming up through each gear. Some of the “fixes” that I’ve tried:

1- vvt adjustment
2- Small BRP A/A intercooler
3- Replaced the PC with the PC-Pro
4- Iridium BKR8EIX spark plugs
5- Seafoam (to remove carbon buildup)
6- 180 deg. thermostat

I finally got to a dynometer. After welding in the bung for the probe, we tried 4 different pulls – each time the dyno operators stopped the pull due to overly lean conditions. After each pull, I would increase the PC-Pro in the Green (1,200 – 3,000) and Yellow (3,000 - 5,000) range. At the end, I believe that I had the PC-Pro maxed out (in the 3,000 – 5,000 range):

Green (1,200 – 3000 rpm) =6
Yellow (3,000 – 5,000) = 8
Red (5,000 – 7,000) = 4/5
Yellow/Blue = 8
Red/Blue = 8

Attached is a PDF file with the black line showing the A/F ratio. Any guesses what could cause the lean conditions in the 3,000 – 5000 rpm range? Is low fuel pressure suspect?

2002 / MP62-S3 (105mm-65mm) / BTB / Small BRP A-A Intercooler / NGK BKR8EIX plugs / PNP-PC-Pro + J&S (Sensitivity = 1:00, Start=full CCW, Rate= 1:00) / TDR Heat Shield / Good-Win-Racing RoadsterSport Mid-pipe / VVT Adj. / 93 Octane gas

Thanks,

MiataVOL

[Bo0osted]

Is it possible for you to upload a larger pic of ur dyno? It's very hard to read. People may be able to offer better advice if they can read the graph.

[MiataVOL]

Please pardon the small graph (I gave up after 1/2 hour). The really squiggly line in the lower right is the A/F. It is about 12.75 at 3,100 and rises to 13.0 when the pull was stopped at 4,000 rpm. [I'll keep trying to post a larger graph].

Thanks,

MiataVOL

[Bo0osted]

If it helps any, my 99 (with a high flow fuel pump and regular Powercard) runs too rich. Like under 10.0. I'm hoping the PC-Pro will fix my problems. It could possibly be that you need a high flow fuel pump but I'll let the experts here chime in.

[MiataVOL]

Attached is a (hopefully) improved image.194

[chuckerants]

Attached is a (hopefully) improved image.194

I can't figure how WTH I'm looking at.

[bogey]

That looks a bit like mine when I brought it to Tom last month... My graph was all over the place like yours.

I have a vacuum leak on the flex intake hose where it was attached to the MAF and TB. I had "rolled" the ends of the tube back into itself before connecting to clean up the install and hide the ragged edge, but that was enough to cause pinpoint leaks under boost.

Also, I had a boost leak on the boost hose that went to the JRPC. It only leaked when it saw significant pressure (>5psi) and caused the PCPro to deliver less fuel than it should.

Doublecheck (no - triplecheck) everything having to do with vacuum and boost. These were difficult to find becuase they were intermittant and only occurred under boost. The usual spray at idle did not detect them. Only after removal of intake were dust tracks visible.

Also, my cat was clogged and I was losing 20-30 hp. Once that was opened up, pinging stopped.

[Tom @ Fast Forward]

Also look where the vacuum/boost line is connected to the intake manifold. There's a thread around here that shows how NOT to connect it. If the boost makes 8PSI, for example, and the card only thinks it is at 5 PSI, for example, the card will not supply sufficient fuel. We have found that problem on several cars now. The connection has to be tight at all joints/connections.

Also, the cruise control barb on the intake manifold is a much better place to get the boost from than the dummy throttle body.

[MiataVOL]

I’ll plan to check for leaks this weekend (its been near 100 in the afternoons).

The vacuum/boost line is connected to the DTB with the stock BRP hose/connection. I’m game to try anything that may improve the situation. Would someone please describe the location of the cruise control barb? [My base 2002 didn’t come with cruise.]

If the intent is to increase the pressure signal going to the PC-Pro, how about tieing into the pressure tap on the discharge of the blower?

MiataVOL

[Tom @ Fast Forward]

Here is the old thread about the problem with the boost pickup in the DTB.

http://www.fastforwardsuperchargers.com/forum/showthread.php?t=553

The cruise nipple is on top towards the rear of the manifold. If you don't have cruise, it should have a rubber cap on the nipple.

[MiataVOL]

1. My DTB is the older BRP (cast) type, and not the later welded type that caused some problems with the vacuum / pressure connection.
2. I moved the vacuum / pressure to the cruise control barb on the top / back of the intake manifold. No change – the J&S would light up after the car reached operating temperature.
3. I confirmed integrity of the vacuum / pressure line going to the PC-Pro and J&S knock sensor by removing the line from the manifold, and inserting it into a hand vacuum pump. I could pull (and hold for an extended time) vacuum on the line (no significant leaks).

I’m open for suggestions…would there be expected any problem in connecting the vacuum / pressure line into the fitting on the discharge side of the blower? Would this not increase the pressure going to the PC-Pro (eliminating the pressure drop caused by small A/A IC)?

Thanks,

MiataVOL

[Serpico]

I'm not sure that's a good idea. There's about a 2-3psi drop across the BRP intercooler. In my case that would mean I would be adding fuel for 12psi when my engine is really only seeing 9psi and the J&S would be pulling way more timing than was necessary.

You may want to think about upgrading your fuel pump if it's not able to supply enough fuel.

FWIW, I'm able to get 12:1 all the way to redline with my fifth injector unplugged, so the main injectors are indeed able to supply enough fuel. I have the walbro 255 though.

If you still have the OEM fuel pump, so may want to try the walbro 190 or even the 255.

[MiataVOL]

If the only issue in connecting the vacuum / pressure line to the port on the discharge of the blower is the J&S pulling more timing than necessary – the start and rate (amount) of timing that is pulled is completely adjustable.

Has anyone tied the vacuum / pressure line into the port on the discharge of the blower?

What are the odds that I have a low fuel pressure problem? Should I invest in the equipment to check the fuel pressure myself, pay the dealership to check it, or just invest in a new stock (or Wabro) fuel pump?

Thanks,

MiataVOL

[Kyp J]

Way back at the beggining of my supercharging expereince, I was getting intermittant sudden fuel starvation under boost and after thinking about testing options, decided to put in a 255 Walbro and it solved the problem. I think the stock pump wasn't quite up to the job and was failing after heating up (just a theory, knowing the fuel is supposed to keep it cool. Maybe just crappy electrical connections getting hot???) Anyway, it was easier and cheaper than trying to figure out how to install and monitor a fuel pump for a one time problem.

By the way, I originaly thought it was a bad fuel card (ELF at the time) but it wasn't.

[Serpico]

I agree with Kyp J. It's cheaper to just get the Walbro rather than paying someone to trouble shoot your fuel system only to find out that it's marginally adequate.

Yes it's louder than stock , but at least you'll know it's running.... :)

[bogey]

Checking fuel pressure is not difficult. You need a guage and a T adapter line.

It could well be a bad fuel pressure regulator. On an NA, the pressure should be around 50-60psi and the system is supposed to hold ~40psi for 20 minutes or more after shutoff. If the FPR is bad, then the pressure will drop like a rock after shutoff.

A bad FPR will still allow the stock pump to deliver adequate pressure for a non-boosted engine, but under boost, fuel delivery will drop off due to lower pressures.

Replacing an FPR is a lot easier and cheaper (used for $25) than a new fuel pump. A new pump may exhibit the same problem if the FPR is open, then you have wasted more money.

I don't know which year your car is, but on an NA, you can pull off the FPR, and check to see that it is closed and will not allow air to blow through. If it is open, replace it. PlanetMiata, FM, or Mikes Place should have used ones quite cheap.

[Serpico]

He has an 02' and FWIW, even on the puny Jackson Racing M45 kit for NBs, it is recommended that you upgrade the stock pump to the walbro 255.

I believe Tom and Bill (Pulley Boy) both have tested their NBs and found that fuel pressure was dropping off in the higher rpms.

Just get a Walbro and be done with it!

[maggie]

I'm in the middle of my install and I asked Tom about the fuel supply. He indicated that my '02 should not need an upgraded fuel pump. I'd check the FPR first. There was an aftermarket one posted in another thread here available on e-bay.

[Kyp J]

Let me iterate again, my pump would work all the way through the RPM range when it was working but occasionally crap out about anywhere in the range when on full WOT with boost. If you have a good stock fuel pump you won't need a different one with the base kit. If you are having problems, maybe you need a different fuel pump. I don't know what an FPR is but I don't think a 2002 has one. I could be wrong, I usually am.

I found fuel gauges that would mount inside very expensive. You can't have fuel lines inside the passenger compartment so you either have to get a volunteer to ride under the hood to watch the gauge, tape it to the windshield on the outside or get an electronic fuel pump. I thought a new fuel pump the easiest first step (not counting the thousand hours of thinking about it) and it worked out the best. I can't hear my Walbro 255. One good thing about being practically deaf.