Car doesn't like 3.5 bar WCP

[Dr J]

I currently have my car in stock configuration (1979 SC) with the only exception that I have modified compression to about 8:1.

I found that my car runs too lean when the warm control pressure is 3.5 bar. It is 15-16s according to my AFR meter. I can verify the leanness by the feel of the engine while driving. I disconnected and plugged the vacuum line to the WUR which dropped my WCP to 2.7 bar. Car is much happier and the AFRs run in the 14s for full throttle accel for the full rpm range. While still lean for WOT, at least it is driveable. I did lose my accel enrichment feature by doing this.

I reviewed my control pressure table from when I used a DWUR (with a completely different air intake system) and found that I had it set at about 2.5 bar and decreasing as RPM and MAP increased.

I also did a flow test on the injectors and they had good pattern, no leakage, and flowed 175-180 ml per minute. To check for vacuum leaks, I opened the oil tank saw that the rpms went lower.

Any suggestions? Continue looking for vacuum leaks?

[boyt911sc]

Dr. J,

Are you using a digital WUR or the OEM Bosch WUR? What Bosch ID is on your WUR? Do you know the resistance (Ohms) of the heater? What is the profile of your CP vs. time? How long does it take to get from CP to WCP? Asking too many questions? Without knowing these basic data about your CIS, you'll be doing a lot of guesswork to fix your problem.

Not being able to locate the source of an air leak/vac does not mean you don't have any. Test and confirm. Keep us posted.

Tony

[Dr J]

Thanks Tony for the reply and feel free to continue to ask questions. I can get all of the answers but before I go into it, I should clarify that this is while the engine is warm, so all of the transition from cold to warm is out of the loop. The WUR is a 045 and the 3.5 and 2.7 bar WCP are within specs for vacuum attached and removed. If you still need the other info I will get it and post it.

[boyt911sc]

Originally Posted by Dr J

Thanks Tony for the reply and feel free to continue to ask questions. I can get all of the answers but before I go into it, I should clarify that this is while the engine is warm, so all of the transition from cold to warm is out of the loop. The WUR is a 045 and the 3.5 and 2.7 bar WCP are within specs for vacuum attached and removed. If you still need the other info I will get it and post it.

Dr. J,

What are the two (2) most critical parameters that would directly affect the fuel mixture composition? Fuel and air. If your fuel supply is within acceptable value, what would cause it to go LEANER? Either it is set lean (fuel mixture/FD) or your are getting unmetered air some where.

The problem I find sometimes with people using these expensive AFR devices is not knowing or verifying the presence or absence of air/vac leak (significant) in the system. You may not have a vacuum leak but you don't that for a fact. And most of us including myself tend to believe everything is OK. Unfortunately, life sometimes is not fair.

Anything that could go wrong will go wrong. This is my mantra. Keep us posted.

Tony

[T77911S]

air leaks
what happens when you adjust the mixture richer with it at 3.5bar.

been fighting an air leak on my 930 for a looooong time. same as you. AFR in the 15's, but, it would start in the low 14'sto upper 13's and go leaner. i can also feel it when driving when it is lean.

tony, it was a vacuum leak in my diverter valve. with the leak fixed now i am extremely rich, 12.5 at 3k but it likes it.

[Paulporsche]

From personal experience, you can't go wrong listening to Tony.

I also agree with what T77911S said. I haven't read anywhere that you have tried to adjust your mixture, or tested it at idle.

[Dr J]

What Tony said makes sense it must be an air leak somewhere. I have adjusted the idle since I have an afr meter. However it goes lean as you accelerate through the rpm range.

Will spend some time this weekend checking for air leaks.