Way too lean

#1

I just returned form the dyno and my car is running way too lean and making only 131hp. The lean condition seemed to happen suddenly (the cars was running good then seemed to go flat. I lost 4 seconds per lap). It is lean (15.3 A/F ratio) through the entire rev band. Two different ECUs and A/F meters produce essentailly the same results.

I have replaced the injectors with rebuilt and blueprinted RC engineering units. Compression is good, rebuilt head recently fitted, all new gaskets and lines.

I have not checked the fuel filter yet (duh).

Any other ideas?

Don

#2

Check the fuel pressure at the rail (and the FPR). My first place to start looking. Next, ask Jim Levie.

#3

I’m with Craig on this…

Seeing the same results with two different DME’s and AFM’s and having known good injectors in place rather suggests a fuel pressure/delivery problem or a pretty bad intake leak. The former is easy to test with a fuel pressure gauge (the test procedures are in the Bentley manual). The latter is best diagnosed by having a smoke test run, but critical inspection of everything associated with the intake and judicious application of carb cleaner should reveal any gross intake leaks.

After that you need to consider the possibility that the engine temperature input to the DME is invalid or that the data from the O2 sensor is invalid. The temp sensor and associated wiring can be tested and verified. But for the O2 sensor, just replace it with a new OE part.

#4

Thanks Guys.

What should the pressure be at the rail?

Jim - What do you mean by “judicious application of carb cleaner should reveal any gross intake leaks.”? Do you mean just cleaning for inspection or is there some technique that I may be missing.

My car is currently locked up in my mechanic’s shop so I won’t be able to try anything until Monday.

Don

#5

On the Motronic, the O2 sensor is bypassed at WOT. Mixture is controlled by the map in the ECU, so checking the O2 sensor will gain you nothing.

I like the idea of the air leak…intake billows is an excellent place to start. After that, inspect the water hoses/fitting on the side of the TB.

If there is no air leak, the next place to check is the FPR. Replace with a new or known good one and check again.

BTW, over 15 to one will melt pistons quickly…be careful!! Chuck

#6

donstevens wrote:

[quote]Thanks Guys.

Jim - What do you mean by “judicious application of carb cleaner should reveal any gross intake leaks.”? Do you mean just cleaning for inspection or is there some technique that I may be missing.
[/quote]

The motor will happily burn carb cleaner as fuel. Spray carb cleaner at a suspected vacuum leak. If there is a leak there the motor will surge because the carb cleaner will get sucked in as fuel.

#7

That is true if the WOT switch of the TPS is good.

#8

I had a similar problem - turned out to be the fuel filter. Should be something you change anyway. Isopropyl alchohol in a spray bottle will also work in trying the find a vacuum leak. just spray around hoses/bellows/etc. The hose going from the valve cover to the throttle body is a common source of leaks as well.
Ed

#9

Good stuff guys, Thanks.

Keep the idea coming. Troubleshooting starts Monday.

Don

#10

donstevens wrote:

Just to clarify for Don, you do this while it’s running and if there’s an intake leak it will get sucked in and you can hear the engine pitch change.

#11

Thanks for all of the tips guys. After a week of work and a couple trips to the dyno we finally have good fuel pressure, fair A/F ratio, but still lowsy power.

What we have done so far:

New Fuel Pump
New Fuel Filter
New Fuel Pressure regulator
New TPS - the previous one was dead
Recent RC engineering injectors.

Fuel pressure is 38 at idle, 45 at WOT, AF ratio is now in the low 14s and it is only making 135hp…WTF? I thought racing was supposed to be fun. :angry: All of this “fun” also caused me to miss this weekend’s race at Homestead :frowning: …Well, there will be more race weekends.

We are going to double check the compression and play with a couple more AFMs but after that we are out of ideas. I am starting to think “junk yard motor”. Any more ideas from the Spec E30 community?

Don

Don

#12

To complete the diagnostic picture you need compression and leak down numbers. It might be a dumb question, but has the exhaust been swapped to the Spec E30 exhaust (and the cats deleted)? Clogged cats can seriously reduce power.

#13

10-4, Spec exhaust is already on the car.

Previous compression check (by another shop) appeared good. We are going to do it again for a “second opinion”.

Thanks

#14

Also get leak down numbers as they are a better assessment of the condition of the valves and rings.

This sounds so dumb that I hesitate to bring it up, but have you verified that the throttle body butterfly goes to WOT when the accelerator pedal bottoms out? I leave it as an exercise for the reader to figure out why I’d ask that question…

#15

If it doesn’t, that would provide a rich condition, would it not?

I’d still look for a vacuum leak if you are still too lean. What kind of vacuum are you pulling in the intake at idle?

#16

Excellent point on the WOT issue. I know of at least 2 cars that restored performance by adjusting the throttle cable. Also, the plastic clip on the throttle lever can break leaving slack in the cable.
Ed