420a-t running lean

[Carter_95RS]

Found it, I thought i remembered reading this on here.

the local AutoZone carries the replacement Bosch o2 sensor for it, that way if it fails I don't have to wait for a replacement.

If you weren't aware that you could replace the AEM UEGO o2 sensor with a Bosch over the counter one heres the part number. Bosch LSU 4.2 17018

Dave, you were correct.
Price:
$65.99

 

[david-b]

Found it, I thought i remembered reading this on here.

Dave, you were correct.
Price:
$65.99

Sweet. Amazingly been about 2 years since I bought the one from AZ and still 'guessed' the right price.

 

[96 420a-t]

Ok well I'm gonna revive my old thread instead of making a new one...

Soo here's what's up. I have checked everything I can think of.

-my fuel pump is correct and creating pressure.
- fuels sustem has no leaks at 140 psi.
-fmu is functioning.
-plenty of injector flow (275cc)

Now what else is there that could be causing me to go lean? What else should I check? I have done all I can think of.

Side note... my 96 has no fcd but does not fuel cut.

I can boost 4psi no problem, at 5psi it starts to go lean, at 6psi it starts to miss from being too lean.

 

[Carter_95RS]

Are you useing a walbro 255hp pump? If not the only other thing I can think of is that the fittings on your fmu may be to small not letting enough fuel pass through.

 

[96 420a-t]

I just swapped out the gss317 (255 low pressure) for the higher pressure gss342. What size fittings should I be using? I am plumbed with barbed fittings that fit the factory return hoses.

Now my main concern is why is my 96 able to run boost and not hit fuel cut without a FCD? This perplexes me...

After more research I have seen that a rich misfire will read as lean since there is still o2 coming out of the exhaust. I think that I'm running too rich and misfiring. I'm gonna put my stock injectors back in and see if that helps.

 

[Carter_95RS]

I just swapped out the gss317 (255 low pressure) for the higher pressure gss342. What size fittings should I be using? I am plumbed with barbed fittings that fit the factory return hoses.

Now my main concern is why is my 96 able to run boost and not hit fuel cut without a FCD? This perplexes me...

After more research I have seen that a rich misfire will read as lean since there is still o2 coming out of the exhaust. I think that I'm running too rich and misfiring. I'm gonna put my stock injectors back in and see if that helps.

Unless you have something to control the larger injectors then you are probably running rich.

Also, since your car is a 96 you may have an early fuel system car, like I do. If that is the case it would explain why you don't need a fcd. The fuel system changed in 96.....just a thought.

 

[96 420a-t]

Oh well looks like I have a missing. Link for sale. Also in need of a safc. Thanks for the info

 

[96 420a-t]

So new update. I swapped out my bigger injectors for some stockers. I am still showing lean on my a/f gauge. I'm pretty sure its the rich misfire still. I found out I'm running 58-55 psi fuel pressure at idle. Now I know this is too much so I am getting a new regulator as we speak. Also I just noticed under deceleration my car is backfiring pretty hard. Now also I kept my foot in the throttle to boost till it missed. It started to miss, would not accelerate, started back firirng all while showing lean. So I'm pretty sure its a rich misfire.

Any thoughts?

 

[96 420a-t]

So new update. I installed a new MAP sensor though it might help. It kinda did but not really. I am waiting for my cheap-o FCD to come in to see if it is in fact the missing link. For the time being I am running FCDless. It performs the same as when I have the missing link installed except some backfiring and idle issues.

I swapped out my old ngks with some new ones gapped at .032". Brand new map sensor. Stock injectors. I tested the fmu and it is working all the way to approx 130psi. So with what I have seen everyone else running minus a FCD I am running lean at about 4psi.

I'm at a loss still. Any other ideas.

 

[Shake_Zulla]

So new update. I installed a new MAP sensor though it might help. It kinda did but not really. I am waiting for my cheap-o FCD to come in to see if it is in fact the missing link. For the time being I am running FCDless. It performs the same as when I have the missing link installed except some backfiring and idle issues.

I swapped out my old ngks with some new ones gapped at .032". Brand new map sensor. Stock injectors. I tested the fmu and it is working all the way to approx 130psi. So with what I have seen everyone else running minus a FCD I am running lean at about 4psi.

I'm at a loss still. Any other ideas.

Why don't you sell it and but a gst? Can't remember if you covered it already but is the voltage to the pump acceptable? I like dark stabbing too.

 

[96 420a-t]

I'm pretty sure it is but ill check it tomorrow just in case. I am running out of dark to stab. Ill know for sure when I get an fcd. I think now what I'm getting is fuel cut. It boosts fine until 4psi then goes lean till it starts to miss.

 

[96 420a-t]

Another boggling update...

I put my missing link back on after I de-modified it. I found out for sure what fuel cut is. Now I've done a bit of searching and have gotten lost. Are there any othe causes of fuel cut? I see no way that the missing link is leaking because when I blow into the bottom of it it hold, unless it is leaking under higher pressure. But when I take it off and run no fcd it doesn't buck but it does hesitate and run way lean. I just need to get this working till I can afford ms.

Any ideas?

Bump

 

[96 420a-t]

Re-bump

 

[Shake_Zulla]

I have been laying awake at nights running your scenareo over and over in my head... well actually I've been sleeping just fine but I was thinking about this and I have come to this realization. It has to be something with the fuel. Reason being is you are running alright at low boost. Have you checked these things?

Volts to fuel pump.
in and out on FMU is correct.
no blockage in line.
Fuel filter clean.
how old is your gas?

I don't think the missing link is leaking at high pressure cause if you blew into it you could probably blew harder than 5 psi cause thats nothing. (There is no way I could not make that sound dirty, sorry). The only other thing I could thing is that there is a small fitting somewhere in your fuel system allowing the pressure to be fine but hurting your volume (you probably know that these are 2 different things, pressure and volume). You could try deleting the stock pressure regulator too on the off chance its holding something up...

All things being said maybe its time for a wideband.

 

[96 420a-t]

Well the voltage to the pump is bueno, no kinks that I can see, but I didn't look that hard. I've checked the fmu install 4 times and everytime its right, go figure. The reason I'm looking at the missing link is my car boosts the same with or without it. Filter is questionable but since I'm broke it'll have to do for now. Gas is new, under light throttle closed loop anything over 1psi goes lean. Under WOT it goes to 3psi before it goes lean. And I tried to reinstall the ML and watch the voltage coming from the MAP sensore not going over 4.3v but my car won't stay running with the ML. So its out.

I am going to try the zener diode mod to see if that fixes until I can afford a FCD.

 

[96 420a-t]

So I verified that my missing link is functioning. MAP sensor voltage never goes over atmosphereic. I replaced my fuel filter and reverified the connections were right. So once again I'm looking at my fmu being faulty.

Any one have a link or diagram on verifying the assembly of a 12:1 fmu?

I hooked it up and pumped pressure to it and pressure did rise to over 110 psi.

I'm ready to go back to n/a at this point.