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Thread: Too lean on boost - consensus?
05-25-2006 10:14 PM #1
Too lean on boost - consensus?
Hi. Here's the quick history since this is my first post on this forum (I'm an e28'r normally). I have an '86 535i that I have turbocharged with a TCD stage 1 turbo system (including new upgrade injectors). I dearly wanted to go to 5er Fest this year and had been granted an autocross position, but now I'm staying home. I am running too lean on boost. Here's the dyno scenario I went through today:
At idle: Runs fine. Vacuum pressure is ~18lbs, fuel pressure ~35 lbs, dynapack registers AFP at ~14.
At moderate throttle, no boost: Vacuum pressure approaches zero, fuel pressure rises to ~43 lbs, AFp at 13.
At boost: At only 4 lbs boost (no more tried due to lean nature), fuel pressure exceeded 80lb gauge (pinned the needle as expected), AFP went to 12, then spiked into the 20's all of a sudden. At the same time, the car physically showed signs of lean burning (i.e. spitting and chugging).
I have plenty of vacuum and fuel pressure, but run lean on boost when I shouldn't (according to all the other indicators). After looking at the archives on this forum, I have a definite target for the culprit: the chip sent with the package.
So that's my question. Could there be any other reason for the lean running other than the chip? All the past posts seem to indicate the chip as the problem. Unfortunately, a lot of posts didn't have a resolution posted to them. Maybe the joy of having fixed the problem prevented any further comment? Regardless, I'd appreciate any agreement or other ideas anyone can offer.
Oh - quick addition. When I left the dyno and headed to my parents' car lift, the car ran REALLY badly on boost. I may have been running lean for a while, but on the way to the farm, the car would buck and shudder while on boost (never happened before). After letting the car sit in the garage bay (I did some minor work such as relocating the boost gauge and AFR gauge) it ran really well..... DAMN! I HATE it when a car fixes itself! It's the worst feeling in the world to think that you haven't fixed a major problem.... chance has! Argh!
05-26-2006 04:21 AM #2
Re: Too lean on boost - consensus?
I'm Pretty sure the TCD only adjusts timming and leaves the fuel maps un touched. I could be wrong though. Fuel supply / control is usually up to you with the TCD chip. most guys run a FMU with bigger injectors and adjust the AFM. for low boost( under 1 bar). But most serious turbo tunners use at least a piggy back or full stand alone engine control system. ANYWAY.......
What kind of FMU / Rising Rate Fuel Pressure Regulator are you using? and what flow rate injectors are you using?
Bottom line is you need more fuel under boost. A/F ratio should be around 12:1 under moderate boost and slowly goin down( more fuel) as boost increases.
05-26-2006 03:56 PM #3
Re: Too lean on boost - consensus?
I'm using the BEGI rising rate fuel pressure regulator with the TCD kit. I haven't been able to get the exact amount of fuel pressure nailed down, because the gauge I used at the dyno only went up to around 100lbs and I pinned it there while on boost. The injectors are 36# injectors also new with the kit.
As another interesting bit of news, I finally got my Autometer air/fuel gauge and boost gauge installed. The A/F gauge reads rich at idle. As I accelerate, the boost gause goes to zero and the A/F stays full rich. As I start to go on boost, the A/F is still rich. As I continue on boost (very shortly.... maybe at 5-6 lbs) there is absolutely no signal from the oxygen sensor to the gauge (no lights are lit up at all). Could that be the culprit? I installed a brand new sensor when I put the kit on.
05-28-2006 05:50 PM #4
Re: Too lean on boost - consensus? (part 2)
So I drove around and paid more attention to my gauges. I consistently lose A/F ratio signal at 4500 rpm's in every gear. The amount of boost I'm under during that time varies. Sometimes I'm at 7lbs, sometimes I'm at zero. So I'm guessing it's not the amount of boost that's the problem. Again, I'm led to believe it's a problem with the oxygen sensor or the ecu. What does everyone else think?
Oh - and I don't think it's the fuel pressure (although not 100% sure). Since I'm getting the same problem at 4500 rpm's on boost and without, the stock pump should be doing fine, right? Especially since I measured the pressure at at least 100lbs to the fuel rail. The TCD kit never included a high pressure inline pump, even as an additional item, so I would guess the stock unit normally does okay.
Since this is my first experience with a turbo, I'm doing a lot of guessing, but it all seems to make sense to me.
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