Lean Spikes Under Boost

[starfish]

My bottom end is all stock.At WOT I get bad lean spikes.Its been this way for over a year.I try to stay away from WOT.So its okay to get bigger injectors with a stock ecu?mods(E-fcd,Blox bypass valve,12/1 Vortec fmu,aem WB,tial WG 7psi,intercooler,no boost leaks)My A/F #s are allmost identical,rich at start up,14-15 at cruising speed (highway),at wot it spikes lean around 17 then goes back aroud 15 or so.plugs are light brownish

 

[starfish]

You can go bigger to an extent, IIRC 270 is about the max a stock ecu will run. As far as your 14/15:1 while cruising, thats actually about where it should be. Your lean spike when going WOT could be a number of things. Do you have a fuel pressure gauge, what happens to it when you stomp on the gas? Have you disabled the factory fpr?

Stiil use ffpr.FMU is between fpr and tank.I didnt know I could use injectors bigger than stock with factory ecu.I rather be on the rich side.What size and brand would work best with my set up.I will order sap.

 

[starfish]

Like T is for TURBO said, an exhaust leak is more likely to make the car run a little rich; that's true for all cars -- 4G63 or 420A. Your wideband is probably reading really lean, even though the AFR is closer to stoich.

so even though my #'s are alittle on the high side,and my plugs are light brown,I should be ok?

 

[VelocitàPaola]

so even though my #'s are alittle on the high side,and my plugs are light brown,I should be ok?

I don't know, do you have an exhaust leak too?

 

[starfish]

I don't know, do you have an exhaust leak too?

The exaust is completely welded,until it reaches the muffler in the back.Ive allways blamed the lean spikes on the 12/1 fmu.Being I use the car on a daily basis,I'd like to get the best fuel management possible.Would slightly bigger injectors richen it up alittle,or would it just create other issues?I really want the best way to tune a 420A-t,and to keep it reliable at the same time.

 

[VelocitàPaola]

The OP of the other thread had a completely different issue so I split your posts into a new thread.

It's definitely possible that the FMU is causing a lean condition under boost. It just adds fuel linearly, which doesn't always correspond to the engine's fuel requirements. An S-FMU is a step above an FMU. You can tune it and use larger injectors.

Of course, something like MegaSquirt EMS is the only way for full control.

 

[starfish]

The OP of the other thread had a completely different issue so I split your posts into a new thread.

It's definitely possible that the FMU is causing a lean condition under boost. It just adds fuel linearly, which doesn't always correspond to the engine's fuel requirements. An S-FMU is a step above an FMU. You can tune it and use larger injectors.

Of course, something like MegaSquirt EMS is the only way for full control.

I'm not too familiar with a S-FMU.Do you need a s-afc to tune with it,or do you just make ajustments until the A/F gauge(wideband) is showing good #'s?Ive only seen pictures of them.

 

[tec_41]

I'm not too familiar with a S-FMU.Do you need a s-afc to tune with it,or do you just make ajustments until the A/F gauge(wideband) is showing good #'s?Ive only seen pictures of them.

With an SFMU you don't need anything else, the SAFC wouldn't be needed. As far as I know, you can adjust the base fuel pressure with it, so it's essentially an AFPR and an FMU in 1 unit. Someone correct me if I'm wrong...

 

[starfish]

now I have bigger problems!I better start another thread

 

[sestepney]

Buy the Portfueler and be done with it! I'm currently building my 420a and I've read and heard to many bad things about tuning with FMU's so.. I just spent the money and got the portfueler from hahn racecraft.

 

[starfish]

Buy the Portfueler and be done with it! I'm currently building my 420a and I've read and heard to many bad things about tuning with FMU's so.. I just spent the money and got the portfueler from hahn racecraft.

went on their site and couldn't find a price. What did it cost you?How easy is it to tune?

 

[sestepney]

If you buy it from Hahn you'll spend about 1200 but if you ask around on forums and search on ebay you might find someone trying to sell theres. I bought mine off a guy who snapped a bolt on the tensioner and didn't want to rebuild so.. I got it for 600. I'm sending it to Hahn to calibrate it for my setup. I haven't ran my car yet, still a few things needed before I run her but I haven't read alot of bad things on this forum about the portfueler so...