Lean at high boost (>15)

[Sixxshot87]

What are the common causes you guys have noticed that are the cause(s) of running fine up until about 13-16lbs of boost and then car falling on its face from running lean?. I do not have an in car fuel pressure gauge but the rail gauge says its at 43lbs when in idle and O2s read around 800 till around 13-16lbs then drop off to like 50-200 like I'm running out of injector or some thing. I usually run around 22-25lbs of boost but the car is just not having it. If i stayed floored it would just run so lean that making any more boost would be impossible/dangerous. The injector thing doesnt make sense because i have a TT chip mached to 60lb mototrons and have it dialed up to add 20% fuel. The car does not pop out the intake at all like a bad coil pack at low boost or anything. Again the best way I can describe it is like I am running out of injector. I get sufficient pressure up to the boost levels I said then it leans out and does that in-boost lean out sputter with 1-3.5 degrees of knock and a low MV reading. Im ranting now but any past experiences or shots in the dark would help. Thanks

 

[Blazer406]

I think you have a fuel pressure issue at boost. It could be a pump issue.....could be a wiring issue.

My first look would be to examine FP at boost. I would recommend flowing the fuel system with the FP jacked up to 65 - 70 psi. Make a temporary line to go from the bottom side of the regulator to run into a bucket. Cut the regulator up with the fuel flowing into the bucket.

Measure the output (gal/min) and we can see if it is working decently.

 

[Sixxshot87]

crank it up on the regulator with an allen wrench right? (as opposed to brake boosting it). or what. Not the smartest question but can the regulator even be adjusted that high.?

 

[Pronto]

Sounds like the fuel system has an issue. I'ld start with the fuel pump. Get a test gauge for fuel injected cars and tape it to the windshield. Watch it to verify you get getting 1:1 fuel pressure rise with boost pressure. Could be anything in the system though ie; clogged fuel filter, clogged fuel return line, bad wiring, etc. Until you find why you are going lean don't to go to high boost. Your playing with fire.

 

[Otto J]

Is it possible the the chip rest and you are no longer adding the 20%?
If I tune a car that requires anywhere near that much fuel I have it reburned just in case someone disconnects their battery and resets the chip.

 

[Blazer406]

crank it up on the regulator with an allen wrench right? (as opposed to brake boosting it). or what. Not the smartest question but can the regulator even be adjusted that high.?

Yes... it has worked for us...... car off.... key on...... batt charger hooked to battery (simulating voltage coming from alternator if the car were actually running)...... gauge hooked up....... return line ran from bottom of regulator into a bucket....... with fuel flowing into bucket..... jack regulator up to 45 psi + the boost you are running i.e 20 psi boost would be 45 + 20 = 65 psi

I use a 3 gal or so car wash bucket that has graduated lines on it you can see down the inside of the bucket so you know exactly when a gal has been pumped. I then see exactly how long it takes to pump a gal of gas.

If memory serves me right... our single 340 flowed thru the regulator @ 70 psi took just over 1 minute to flow 1 gal of fuel.

FWIW..... we had a wiring issue once.... it took over 3 min for it to pump a gal.

IMHO.... once you do it one time...... it is pretty easy to double check again later if you suspect there are issues with fuel delivery at boost.

HTH

 

[Blazer406]

Is it possible the the chip rest and you are no longer adding the 20%?
If I tune a car that requires anywhere near that much fuel I have it reburned just in case someone disconnects their battery and resets the chip.

Great point Otto. I agree 100%.

 

[dennisL]

I solved that problem by replacing the fuel filter (under the driver-side door). I've been told that a collapsed sock on the fuel pump will have the same symptom.

If you do the fuel pressure test as suggested, you'll see the pressure at the top end is not adequate.

Dennis

 

[Razor]

Sounds like a new fuel pump and filter will eliminate a lot of guesswork troubleshooting.

1 hour to replace those parts or 3 hours to rig things up and get back to square one.. needed to replace the pump.

On the GN a pump swap is no biggie and can be done in your driveway with simple tools.

 

[Blazer406]

Sounds like a new fuel pump and filter will eliminate a lot of guesswork troubleshooting.

1 hour to replace those parts or 3 hours to rig things up and get back to square one.. needed to replace the pump.

On the GN a pump swap is no biggie and can be done in your driveway with simple tools.

Do you fancy yourself as a mechanic..... or parts changer?

Sorry Julio.... had to poke you a little.

In reality... we rigged up and flow tested the IROC in about 15 min.

Reality is.... you might change the pump and filter out.... and still have the same issue..... might be in the wiring...... power or ground..... or a weak relay with corroded contacts.

Flow check it ..... and you will know if it is right.

With the current issue... even if you do swap the pump and filter out... I'd still flow check it.

 

[Razor]

Do you fancy yourself as a mechanic..... or parts changer?

Sorry Julio.... had to poke you a little.

In reality... we rigged up and flow tested the IROC in about 15 min.

Reality is.... you might change the pump and filter out.... and still have the same issue..... might be in the wiring...... power or ground..... or a weak relay with corroded contacts.

Flow check it ..... and you will know if it is right.

With the current issue... even if you do swap the pump and filter out... I'd still flow check it.

Its Ok brother..

I look at things sometimes like this. labor time whether I work on the car or take it somewhere has a cost. When i do work myself, I have that extra amount of lee-way when it comes to $$$ and parts. meaning if a fuel pump/hotwire and filter cost me 140.00.. and I can knock it out in an hour.. vs 3 hours subjecting the car to punishment.. i'm way ahead.

If the fuel pump doesnt solve it.. I know where not to look for the problem.

On expensive parts you need to spend the time and diagnose. But a GN with a leaning out issue.. arrows point in the same direction.

This coming from a person with a leaning out problem that cost him 3 head gaskets and ended up being an intermittant hot wire relay cuasing the problem. But I did fuel pump and filter first.. it bit me again.. did the flow tests.. they where all good.. until I data logged FP, thats when I caught it.

Home made relay kit on the car did me in. :redface: