mjshira

I've been working to get my car running correctly and I am down to this final lean condition which I wanted to pick the brains of some of you about. My buddy Brent and me put a data logger on the car with a wide band o/2 sensor. We found that the car is lean everywhere..while cruising part throttle the car maintains a 15.1-15.3 a/f at 2000/3000/4000/5000/5500 rpm. when doing wide open throttle runs from 2000 rpm up here is the results.

wot 1st run 2nd run
2000 13.2 13.4
3000 13.2 14
4000 14 14.1
5000 14.3 15
6000 13.2 14.5

as you can see 3k and up it gets really lean...this is where it pings like crazy and stumbles throughout the rpm range...

So tonight I changed the fuel pump. This was one of the parts I'd not replaced on the car and since the car has about 100k on her (rebuilt engine) I wanted to eliminate this variable.

I took the car out after changing the pump and she still pings

I've read through a bunch of threads and I've learned that the DME controls fuel to the engine based on input signals from the AFM and o/2 sensor. I've got a new o/2 sensor and from what I've read even if it were bad it wouldn't cause the engine to go lean enough to ping.

My AFM is a recent replacement from vertex so I question if it is bad. I also replace the idle control valve.

So I am at a bit of a loss.

Can anyone offer a theory or similar experience?

Sire

AFM i would buy allways stock, but intrested in a upgrade try the MAF, incl piggyback from vitesse you can control the fuel then.

Fast4525

Is your engine 100% stock?

pat056

I have the same issue. I've gotten a lot of advice from fellow rennlisters. I don't know how to highlight the thread, but it's on the Racing and DE forum titled "Dyno".
I'm changing my fuel filter this w/e and going to verify my 02 sensor is the same as the one I replaced last year. Also going to run 100 octane unleaded until I confirm my 13.9 readings. 2 years ago, mine was 12.5 w/the only modifications being to improve my pick-up from my fuel cell.
Let me know what you find out? I'll do the same.
Just out of curiosity, have you pulled the plugs? Are they whitish grey? I pulled mine and all were the correct brownish color.

mjshira

Mine is in the mail now. I want to fix the lean condition first. Then approach the kit.

mjshira

The engine has C2 sport cams. But I've been told they are mild and they won't cause a problem. The engine is rebuilt by EBS.

mjshira

The plugs are new. I've replaced them in the last 1000 miles. The lean condition exists across the range. We did the LM-1 logging across nearly the entire RPM range. So from 2k-redline we saw lean condition with the worst coming around 4k.

I've got a new fuel pressure regulator. It seems like that will be a pain to change but I need to tackle that next before I install the MAF kit, large injectors and piggy back. I want to isolate this problem before I change more things.

fast951

It appears that you have the best tools to figure out the problem: A good helping friend, the list and a Wideband.

- Make sure the Wideband sensor is calibrated before your next test.

- Vacuum leaks will cause a NA engine to run lean. So does fuel delivery (pump, FPR, Injectors,...). Of course a faulty AFM or a WOT switch not engaging will do the same. While at it, make sure ALL of your ground connections are good, a faulty ground connection will cause all sort of issues.

So you think you have enough to do this weekend, or should I add a few more items on the "to do" list.

mjshira

John

Thanks yes I have a lot to do and I am out of town 1/2 the weekend so the best that I will probably get will be just getting the car apart. Does anyone have a recommended approach to changed the fuel pressure regulator? I was thinking I'd removed (as you view the engine) the right side of the intake system to expose the area underneth to reach it. Going the other way would involve taking the entire heater system off then the intake so it seems that this is the best approach. Thoughts?

pat056

Where's the WOT switch? Is there a way to test it?

mjshira

When I changed the AFM and throttle cable I had to test WOT. You use the hammer and then put the throttle peddle to the floor. The hammer tells you if the switch works. In my case it did. Because my car is lean across the entire range I think it is a fuel delivery issue. Either A) the fuel system has an issue (and I've changed the pump and filter so that is 1/2 the equation there) or B) the DME for some unknown reason is giving the engine enough fuel.

Once I've changed the FPR I will then check fuel pressure at the rail. Then I will replace the AFM with the MAF kit and see where things are. My 'hope' is that it is the FPR. I don't think I have a vac leak at the intake because that would be on one cly, one bank of cly, very remote it would be even vac leak across the entire engine. I will also validate vac line to the FPR.

Loads of fun right guys!

fast951

You could have a vacuum leak anywhere (ICV, base of TB,.. ). Unless you test for vacuum leaks, I would not add any new components on the car.

mjshira

Vac leak at the idle control valve? Ok, I'll check for that I assume a little bit of water or just ones finger to see?

I will check all the throttle body connections. Going to have to get into those anyway because I'll be removing 1/2 of the intake system anyway.

Best way to check for vac is?

swmic

I know some old hot rodders use to take starter fluid and spray it around. If they found the location of the vacuum leak, the rpms would suddenly increase.

sperki11

Isn't the stoichiometric a/f mixture around 14.7 parts air to 1 part fuel. Any reading less than 14.7 would be considered rich, therefore a reading greater than 14.7 would be lean. Based on the WOT readings, I would say you're running rich, not lean. Do I have this correct?

I know if doesn't explain the ping...