2.7 CIS won't remain stable - HELP

My 77 with 2.7 with CIS has had a long running problem that has become unliveable.

The car will develop a flat spot around 2200 rpm, to the point of making driving uncomfortable, and it will be difficult to start - requiring 3 or 4 attempts to get it running. The solution has been to adjust fuel pressure and/or replace the warm up regulator.

Used to be this would last for 6 months or more, then slowly detoriate until I had to have my wrench adjust again. Most wrenches would conclude it was a bad warm up regulator (WUR). I went through several WURS over the years and I suspect this was mis-diagnosed.

Eventually the deterioration began happening faster, and it now takes about 2 weeks. I followed the Pelican tech article about modifying the WUR to make it adjustable, works great. But having to adjust it every 2 weeks is out of control.

I think that my fuel pressure is not stable, drifting over time. My adjustment to the WUR is simply compensating for some other problem. I don't have a means of measuring fuel pressure so I can't be sure.

Anyone have ideas on what might be causing this and how I can track it down?

Chuck

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'86 Cab, '77 Targa, Family Truckster

Clark;I really think you need to find a way to measure your fuel preasure as it sounds to me like your warm up regulator is compensating for a weak fuel pump or possibly a plugged fuel filter.I don't know about porsche fuel tanks but I have seen more than one fuel tank that had started to go bad and kept plugging filters.I think you can get a cis fuel pressure tester at JC witney for like $50.00

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Grant 75 911s targa

I agree, you just can't trouble shoot a CIS system without a fuel pressure tester. Bought mine at JC Whitney for $50. Also bought the Probst book on Bosche FI. It has procedures for testing individual components and for trouble shooting problems. The early CIS systems without the O2 sensor aren't that complicated.

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Bill Krause
'79 911SC Euro

I suspect contamination in the fuel too. Rust. That's my suspicion. You should perform an autopsy on parts you remove, especially the fuel filter.

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'83 SC

I have to admit I am way overdue on a fuel filter change, I hang my head in shame. I will try this tomorrow if I can get one locally. That would explain why the problem has gotten progressively worse.

The fuel pressure guage is probably a good investment.

Chuck

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'86 Cab, '77 Targa, Family Truckster

I agree with the others, and esp. suspect the fuel pump. Have made the same experience as well as other guys (there was a similar post recently).

Jens

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