Please help before I drive my FI SC400 into a lake and leave it for dead!

[kc95sc400]

Ok, some of you may be familiar with my car, some not, so here's a couple of links.

Lextreme http://www.lextreme.com/forums/showthread.php?t=8757

Club Lexus http://clublexus.com/forums/showthread.php?t=312268&highlight=boosting+projects

I've had quite a few problems along the way and up until now, I've always managed to figure them out. I am very stumped on this one, I don't know what else to do.

Car: 95 Lexus SC400 with V-9 vortech supercharger. Non intercooled with the piping ran outside of the engine bay. About 135k on the odometer.

Problem: With a COLD start, my AFR stays at about 14.5 to 1 while at idle and while cruising. Goes lean with boost. Doesn't matter if I drive the car 2 miles or 20 miles, the idle and cruise AFR stay at about 14.5 to 1. With a HOT start, the AFR starts out at about 14.5 to 1, but then starts to go rich after about a minute of running, down to 12.5 to 1. Still goes lean with boost. Also, fuel cut operation seems kind of funny, ok at higher RPM's but pulses rich at lower RPM's.

Testing, parts changing:

I've tested and changed a million and one things, which I'll go over, but this first thing is kind of interesting.

With the car HOT, I shut it off, then start back up, AFR is normal. As stated above, slowly goes to 12.5 to 1 after a minute or so. If I disconnect the MAF while the car is running, the AFR stays at 12.5 to 1. When I plug the MAF back in, the AFR goes to 14.5 to 1, then does the same thing, goes down to 12.5 to 1 after a minute.

I figured out that my FPR was leaking vac / boost, replaced it, no difference.

I did some testing on my fuel pump, seemed a bit shady, so I replaced it with a high flow Walbro. No difference.

I checked my fuel pressure, about 40psi at idle. 50psi with the FPR vac line removed and plugged. And..I saw as much as 65psi while blowing air into the FPR with an air gun. This all seems normal.

I have removed or bypassed the charchol canister, the VSV for the FPR, and the power steering idle up swith. No difference. My EGR is and has been blocked for a while now, since before this problem. The only thing, that I am aware of, that is still connected to a vac source is my boost gauge, the heater control valve and the FPR (without the VSV). I've checked everything for leaks, can't find anything.

I took out my plugs, cleaned them. No difference.

I changed some of the piping before the MAF sensor to 3inch. I did have 2.5 inch all the way up to the MAF with a 2.5 to 3 inch coupler on the MAF sensor itself. Didn't make any difference.

Unplugged all of the O2 sensors, no difference. Normally, I have all the sensors installed except the drivers side front sensor, this is where my wideband is installed and is where I'm getting all my readings. I've thought that maybe my wideband is reading funny, but the AFR readout reacts as it should during testing. Shows leaner if I pull a vac line for example.

Within the last year (before supercharging), I have changed the coils, wires, caps, rotors, t-belt, all the fluids and a few other things I'm not remembering at the moment.

I checked every single wire between the ECU and the MAF and TPS sensors. Also checked for shorts to ground, no problems found. Checked the IAT sensor, good.

I plugged the throttle body side of the PCV hoses, no difference.

I've unplugged the coolant temp sensor on the radiator, no difference.

I'm sure there is a few other things I've tried, but I can't think of them all.

I'm really at a loss here. I'm assuming that the lean with boost and HOT AFR decline to 12.5 to 1 are related, but I'm not sure. The only other thing I can think of is an IAC problem. The car runs smooth otherwise, so I wouldn't think it could be a mechanical problem. I also don't suspect injectors, I think I'd also have other issues. Like I said, I'm really at a loss.

Please help!

Thanks for reading my novel.

Khris

 

[striker]

What ECU,

the build up page says something about 315cc injectors, those seem a little on the low side for what you're trying,

if running the stock ecu, ditch it and put a programmable one on, opens up a whole new can of HP worms. doesn't have to be one for a motec buget btw. (for the experts I'm not dissing motec here :sombrero: )

grtz Thomas

 

[Lextreme II]

What is your vacuum gauge read during idle? Why arent you using a Bypass Valve?

 

[cribbj]

Did you change your fuel filter too? Simple suggestion I know, but lean on boost and rich at idle sounds like a fuel starvation problem.

At the risk of having gasoline in the cockpit with you, why don't you run a fuel pressure gauge from the rail so you or a helper can watch it.

Ideally it would be a differential pressure gauge, with one side referenced to the intake manifold, but those are rare and expensive...

Edit: KC - check this out: http://www.lextreme.com/forums/showthread.php?p=84968#post84968

 

[kc95sc400]

I have had a gauge on it while idling.

50psi with the FPR vac line disconnected. 40-45psi with the vac line connected. And 65psi or so with some air blown into the FPR with a blow gun.

Seeing as how this started all of a sudden, I don't think it's a fuel problem. Plus have new pump and FPR. Edit, I think it's a fuel problem but I think something is telling the ECU to take out fuel.

Khris

Did you change your fuel filter too? Simple suggestion I know, but lean on boost and rich at idle sounds like a fuel starvation problem.

At the risk of having gasoline in the cockpit with you, why don't you run a fuel pressure gauge from the rail so you or a helper can watch it.

Ideally it would be a differential pressure gauge, with one side referenced to the intake manifold, but those are rare and expensive...

Edit: KC - check this out: http://www.lextreme.com/forums/showthread.php?p=84968#post84968

 

[cribbj]

Khris, assuming you're still using the OEM voltage switching to your fuel pump, perhaps confirming you have 12-13 volts at the pump under high load would also be a good idea.

 

[kc95sc400]

I do, all of my testing has been done with FP and B+ jumped on the DLC connector under the hood.

KC

Khris, assuming you're still using the OEM voltage switching to your fuel pump, perhaps confirming you have 12-13 volts at the pump under high load would also be a good idea.

 

[cribbj]

Sounds like you might be a good first candidate for that cheap differential pressure transducer!

I'd plumb that puppy between your manifold pressure, and your fuel rail pressure, then hook it up to a Fluke and go for a drive with someone watching the Fluke and see if your fuel pressure varies at all under boost.

If your fuel supply and return systems are working OK, and the FPR is solid, then your fuel pressure relative to the intake manifold should stay rock solid.

I'm going to pick up a couple of those sensors just to play with. They're way cool for the price....

 

[stevechumo]

Man, if I were you, I'd disconnect the supercharger pipe before the TB, but before the MAP to see the difference. This will make the car run almost like stock and it'll give you a base of the issue. Also, I think you're trying to play around with the aftermarket MAF for the fuel controller. I strongly believe that's part of your problem. But who knows the AEM gauge is bad and caused false reading. I haven't touched the stock MAF, I only have the Walbro, the FMU, and running 6 psi with my turbo without any hic cups. This helps me to get the base idea if my car can handle boost, then I'll boost it higher. I've smoked several over 300 hp cars easily with this current set up.

 

[kc95sc400]

It's not the MAFTPro, much of the testing I've done is with it bypassed, running only the ECU and the MAF.

I have a MAF being lent to me, should have it next week for testing.

I can't stress enough, this started happening ALL OF A SUDDEN. I found my old post at the MAFTPro website where I stated that with the MAFTPro bypassed, I was seeing 11.5 to 1 with up to 6psi.

I don't think the wideband is acting up, but who knows. I can feel that the car is running rich, also when it's running lean, It can be felt.

KC

Man, if I were you, I'd disconnect the supercharger pipe before the TB, but before the MAP to see the difference. This will make the car run almost like stock and it'll give you a base of the issue. Also, I think you're trying to play around with the aftermarket MAF for the fuel controller. I strongly believe that's part of your problem. But who knows the AEM gauge is bad and caused false reading. I haven't touched the stock MAF, I only have the Walbro, the FMU, and running 6 psi with my turbo without any hic cups. This helps me to get the base idea if my car can handle boost, then I'll boost it higher. I've smoked several over 300 hp cars easily with this current set up.

 

[kc95sc400]

BTW, I am using the OEM MAF.

Also, I did change my fuel filter a couple of months ago.

KC