Running rich CIS diagnosis

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ps2cho:
Hi there,

I'm hoping I can get a response on here...I am really baffled by this.

I have a 1987 Mercedes 260E 90k miles on the clock /w the CIS-E system.
My MPG is down to 12-13 (5 tanks consistent. I used to get 20-22) and power is low.

My diagnosis attempt so far:

* I probed the o2 sensor and it read fluctuating 0.78v-0.85v -- VERY RICH. Soot on exhaust confirms.
Replaced sensor since it was so burnt up and probably original. Same result so O2 sensor is reading correctly.
* Duty cycle reads 45-50% fluctuating. No vacuum leaks. No rough idle. No misfires. Runs great, just slow and poor fuel economy.
* Coolant temp sensor within spec. 400omhs warm, 2k ohms cold
* Brand new EHA (definitely made starting easier!)
* Plugs/wires/rotor/cap + all fluids are brand new when I tuned the car up 6 months ago.
* Throttle plate is centered and clean. I removed it completely and replaced rubber boot in case of leak there.

The system seems to believe everything is fine, but the O2 sensor and my driving shows it definitely is NOT!

Any ideas where I should look or run tests for?

Very much appreciated!
Robert
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CIS Flow Tech:
Welcome to our Forum,

It sounds like a differential pressure problem or adjustment problem. Call me in the eve CST and we can discuss it and I can send you the necessary info to set it up properly.

Larry
CIS Flow Tech Llc
251-929-3771

ps2cho:
Very much appreciated Larry!

Since you think it could be a pressure issue, I will get the pressures read this weekend since I have a CIS fuel pressure gauge....I think it will benefit diagnosis greatly. So I'll get that done this weekend and probably give you a call Monday :) Have to dig out the kit...

Pressures were dead on 6 months ago, who knows what has happened since then. Plus, I have the new EHA in there anyway so I should make sure no adjustments are needed for that.

Thanks,
Robert

ps2cho:
I ran the fuel pressure test and got the correct 5.5bar upper and 5.1bar lower. Everything seems to be in spec.

I got the O2 sensor issue figured out also. Here is a video of it probed up....Any thoughts? I can't seem to make heads or tails of it. Do you notice anything that would help diagnose issue?

MOV06390DQ | by Aeva

I ordered the EHA test cable harness also late last week so hopefully that gets to me real soon.

Can't wait to figure this out and have a quick car again and back to above 20mpg. It is so slow. With A/C on, it really struggles with accelerating.

ps2cho:
Got it hooked up to an CO2 analyzer....
Looks like my CO levels very low so its not running rich, at least not at idle. Disconnecting O2 sensor makes it drop even lower.

I have a feeling it could be the distributor then -- maybe overfueling on load? I'll shoot you a call tonight Larry.

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