420a-t running lean

[96 420a-t]

So I got my turbo kit installed and running. There is no issues until 4psi. After which it immediately falls on its face and goes way lean. Where should I start looking? Is there any way to see if my fmu is functioning properly? Does fuel cut always buck cause this feels more like a stall.

 

[Slo2gen]

What kind of FMU are you running? What size injectors are you running? Whats your fuel pressure? Are you using FCD or a Missing Link?

 

[96 420a-t]

12:1 vortech fmu

Stock injectors

Stock fuel pressure

Missing link

 

[Slo2gen]

What fuel pump? With the stock injectors at stock fuel pressure the pressure gets pretty high once you get into boost. So if its original it could be on the way out. How are you monitoring your afr and how is the FMU plumed into the system?

 

[96 420a-t]

Fp is a wally 255 the fmu is plumbed in line downstream of the stock fpr. Monitoring with a narrowband a/f gauge

 

[Slo2gen]

Shouldn't you have dissabled the stock fpr to use the FMU? Its been so long since I've looked into this stuff that I can't remember.

 

[96 420a-t]

From what I read on a how to on here you install it after.

From what I read on a how to on here you install it after.

http://www.dsmtuners.com/forums/420a-turbo-conversion/188926-fmu-install-s.html

 

[Slo2gen]

Well if you have access to a pressure tester pump some positive pressure into the vac line going to the fpr and see if the fuel pressure increases 12 psi per 1 psi of air pressure.

 

[96 420a-t]

Good idea. Is it possible that its fuel cut? I thought it was a bucking not a stall.

 

[Slo2gen]

Normally its a buck but I've seen weirder things.

 

[96 420a-t]

Would unplugging my map sensor help isolate my problem. At least point me in a direction.

update: I unplugghed my map and took it for a test drive. I now know that i am not getting fuel cut. i need to look at my fuel pump or my fmu as the problem.

For all of you n/a-t guys what is the part number of fuel pump are you using? i am hearing that there is a low pressure and a high pressure version.

 

[Misterbeechy]

has this been recent.. meaning has this been happening since you started boosting? or did it randomly happen?

reason i say that is because i have heard of missing link having issues reason why alot of people were using the fcd..

so in fact troubeshoot what you can and ask the gurus if fcd could help..

a buck sounds like fuel cut.. usually as the psi rises you'll start to feel it.. small, fast bucking motions if its running really lean

but fuel cut from map sensor will cause a big fuel cut buck

 

[96 420a-t]

it only bucked when i unplugged my map sensor. so now i know that it is just my engine running lean, its mean and fast untill 4-5 psi then goes way lean and falls on it s face. is it possible that my stock injectors just cant flow enough to feed my motor?

is it possible that the internal relief spring on my fuel pump isnt enough?
i have been looking and have found some high pressure versions and some low pressure ones.

according to what i have found the gs317 is a low pressure and a gs 342 is a high pressure.

that being said i have a gs 317... fml

 

[Misterbeechy]

edit** i didnt notice u edited yours while i was writing mines.. disregard

a question is have you ever run over 4-5psi before.. how long have you had this turboed?

 

[96 420a-t]

so now i am going to need either a higher pressure fuel pump or bigger injectors.

what size of injectors would i need to either run a lower ratio fmu or no fmu?

and also who has some or where can i get some for cheapish...?

 

[david-b]

Stock injectors work fine on this setup. I believe my FP was not the high pressure for my same setup.

update: I unplugghed my map and took it for a test drive. I now know that i am not getting fuel cut. i need to look at my fuel pump or my fmu as the problem.

An unplugged MAP sensor will cause problems since the car has no way to see that change in pressure, thus no way to compensate for the change. I'm about 99% sure you are getting fuel cut. When I would get fuel cut the first couple times, it's the car accerlating, then it just basically stops. Car is still rolling obviously, but the rpms drop drastically and nearly throws you forward. I've never had fuel cut stall my 420a. Ideally, the ECU will bring the flow down to idle.

 

[Misterbeechy]

try FCD instead of missing link.. i was thinking the same it.. it would be the map sensor throwing the fuel cut.. like i said.. lean will have small cuts and sometimes wont pass a rpm range.. vs fuel cut where the map would see positive pressure in the IM and and cause the fuel cut..

the injectors are fine and if you run any injectors bigger than stock you would need a way to tune because then you wouldnt have a way to tune idle..

 

[96 420a-t]

Its not the missing link. I modded it and its working like they promised. I have prettu much decided its my fp being the 65psi version. Its been boosted for 2 days now. If I could only get my oil feed to stop leaking.

I'm 99% sure its not fuel cut it doesn't buck. It ggoes way lean loses power and I back off. I hooked up a scanner to the ecu and the map never sees boost.

Based of the fact that at 5 psi my engine is demanding an additional 60 psi of fuel pressure. Add that to the stock 40 to give me 100 psi total. Now with my current pumps internal relief spring being at 65 psi it would cause my engine to starve aroun 2-3 psi.at least that's my logic.

Update: according to my a/f gauge my o2 sensor just died. It is now staying dead center of the gauge under all conditions boost or no boost. Side note. I accidentally hit 6 psi boost which is a new record for my car... I think I found a poaaible problem. After I fix my oil leaks I will replace the sensor. Until then no boost for me.

 

[96 420a-t]

Not trying to bump my own thread here but I got a new issue. I have noticed that under boost and under light throttle my a/f gauge is running as far lean as it can be without it going off the meter.

Mods:
Turbo- ht18s
Inj: stock
Fp: wally 255 low pressure
Fmu: vortech 12:1
Missing link

I have nchecked the line going to the fmu. No leaks, run directly from back of manifold to fmu no splices. All fuel lines are secure and have no leaks. Any ideas?

 

[CODE4]

you need to accurate wideband and fuel pressure readings to properly diagnose this problem, otherwise you are just stabbing in the dark.

 

[96 420a-t]

Its intermittent at best. Some times it rich like its supposed to be. oftent the o2 is cycling like its supposed to.

And since I don't have either I'm gonna stab away. At least until I get my new fuel pump, since I think that's the culprit anyways.

Also does a wide band work with any aftermarket o2 or do they require a special o2 sensor specific to the gauge.

 

[Carter_95RS]

The AEM UEGO uses a bosch sensor that can be picked up at a parts store if I remember correctly

 

[96 420a-t]

well that work out because i just replaced my stocker with a bosch. what is a good wideband to use.

 

[david-b]

well that work out because i just replaced my stocker with a bosch. what is a good wideband to use.

A narrowband O2 is NOT a wideband O2. If you just replaced the O2, you would have had to replace with another narrowband. The stock ECU requires the narrowband to be there and is not fitted for the WB connection.

Most AEMs do come with a Bosch WB sensor along with the gauge. The WB sensor (if needing a new one or whatever) is about $65 IIRC.

Get the WB, and you'll see exactly what's going on with the car then. As stated already, just taking shots in the dark. Trying to figure out a problem off a NBO2 is just not good.

 

[96 420a-t]

damn, i m gonna wait then, ill see what happens after i replace my fuel pump, then ill look into a wideband