Copying my post from volvospeed here...


Ok I'm finally getting a hold on this running lean issue (somewhat)... at WOT, the car is getting more fuel and AFR's are in the mid 12's @ 10/11 psi. During partial throttle though, there is still some issues.

The fuel pump was replaced by a walboro 255, fuel filter has about 35,000 miles on it. The distributor cap/rotor are brand new and the plugs (champion copper) have about 10K miles on them (planning on replacing this week sometime)

Here's what's still going on. If I'm on the interstate going 60 or so mph and I'm in 4th gear and I start to push the accelerator further to the floor, I watch the boost gauge and it creeps up very slowly and up to around 5 psi, the AFR readings get leaner and leaner. It will be in the mid to high 14's or low 15's just cruising not in boost and as I roll into the throttle I can watch the AFR's go higher and higher until they're up in the 17's.

I don't ever go over 5 psi because at that point, I can feel the car wanting to stutter and the acceleration becomes more and more sluggish. If I drop it down into 3rd though, rev the engine a bit and let the clutch out and stand on the accelerator, the AFR's will jump down to the low 13's or high 12's and this is all at 10/11 psi.


**NOTE** This is with the stock ECU and I've tried both the stock boost control solenoid, the GM one I built for my wife's car and the IPD one that I typically use and all 3 show this behavior.


I also feel that it bears mentioning, as I said in another thread, about one in 4 starts is pretty rough. It will take about 8 or 9 seconds of the car trying to start and it seems like it won't start unless I tap on the gas pedal. Once it does fire up I have to keep hitting the gas pedal to keep it running and it stutters really badly but eventually snaps out of it. I'm keeping the camcorder in the car for every start as of this morning to try and film what's going on but I'm sure you guys get a good idea already.

My mechanic that replaced the radiator/heater core and installed the walboro a week ago said it did this on him once but what's weird is that it has NEVER done this. EVER. He said it did this before he installed the walboro so I'm inclined to rule out the fuel pump as the culprit.

Per his suggestion, I also ran a can of BG44K through the last tank of gas last week and noticed nothing different.

I'm beginning to suspect that the fuel pressure regulator could be the culprit. I'm thinking it's not the filter because the car DOES get enough fuel at WOT but for some reason, for a lack of better way of putting it, if you're not going ***** out and you're easing into the throttle, the car will be making more boost but the fuel system doesn't know to start feeding the engine more fuel.

From what I've read, the fuel pressure regulator is what controls this. If the stock unit has a vac line going to it that measures the boost and distributes fuel accordingly (which is what the malpassi does) to me, it makes sense that if the stock regulator wasn't reading it right, this could be causing the problem.

I've heard that the FPR is in several locations depending on what year the car is. From the looks of it unless I'm confused here, it seems that it's on the passenger side just behind the engine block right over the steering rack. Has a few black hoses attached to it.

If this is it and IF this could be the problem, I have a malpassi rising rate FPR that I can install. I've done my searching here and it seems that most agree that this is not an acceptable band-aid to running lean.

The option I would rather try first though is to replace the vac line on the stock FPR (if indeed this is a boost vac line) because if this line had any cracks or tears in it (which is totally plausible) then it wouldn't operate normally.

My question is that if the stock unit is failing and replacing the vac line (if that's what it is) doesn't fix the problem, would it be fine to replace it with this new unit? I'm not looking to run much richer at WOT (which as I understand, this is what the RRFPR does) I'm looking to get more fuel to the engine during mild acceleration because as we found out at the dyno recently, if you stay in the throttle, the car will never get enough fuel. It'll keep making more boost but the AFR's never go below the mid 14's.. so in a way there IS a starvation of fuel at WOT but only if you roll into WOT in a higher gear. For those of you who know, can the malpassi unit simply be set to operate and deliver fuel just as the stock unit does? Or would it just be stupid lean at WOT and no way to control that?


That being said, if the FPR is not the problem here or if I DO end up replacing the FPR with the malpassi unit (or another stock one if that would be in my best interest) and the problem persists, where do I go from there?

I know the fuel pressure sensor could be to blame but I can't find anyone that sells one for my car. Do the 98's even have one?



Anyways, I know this turned out to be a long post but I'm running out of options at this point and desperate for answers or suggestions. At this point, I'm not trying to make the car faster, it's like I'm trying to RE Stage 0 the car and until I can get this fuel issue sorted out, I'm not worried about aftermarket ECU's or running more than 10 psi (stock I guess) boost. I don't see an aftermarket tune as the answer here.

Whether the rough start and the lack of fuel at partial throttle are related to each other, I'm not sure but I do know that both of those issues must be fixed before I consider putting any more money into this car in terms of making it quicker.




Here's a picture of what I'm thinking may be the fuel pressure regulator.. if not, what is it?



I've read that some say the regulator is behind the fuel rail. Here is what's behind mine.



This is listed as the fuel pressure damper.

http://www.partsgeek.com/catalog/199...re_damper.html

On this page, it lists 2 different FPR's. One for return fuel system and one returnless.

http://www.partsgeek.com/catalog/199...regulator.html

I haven't gotten under the car to look and see if the FPR is down there or not but I'm thinking that the thing I took a picture of looks a lot like the return style FPR.

 

Do you have a fuel pressure regulator by the fuel filter?
That may be the regualtor in the pic as well.

Have you connected a fuel pressure guage and drove it to see what happens to the pressure when that happens?

 

No I looked yesterday and it's only the filter there. There is definately a return line back to the tank as well.

I don't have access to a fuel pressure gauge so I haven't tested it when driving.

 

That might be one way to eliminate a fuel issue.