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Old 07-31-2016, 06:25 PM   #1
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Question Can't diagnose my lean condition. (zetec 1.6)

Hello all,

I have an 02 Focus 1.6 Zetec and between my diagnostics guy and me, we can't work out what is making the car run super lean, this leads to hesitation and then the fuel pump cutting out at any speed, no correlation between its cut outs. Sometimes after 70 miles, sometimes after 800 miles.

In open loop the car runs fine (roughly -4 on short term fuel trim and +7 on long term fuel trim), once in closed loop it goes lean til its +18% positive on LTFT and anywhere between -4 to +4 on the STFT. 02 Bank 1 sensor on the downpipe goes from anywhere between 0.1v up to 0.9v constantly changing so that seems fine. Bank 2 sensor 1 at the Cat runs 0.01 up to about about 1v too switiching much less often.

As soon as the car goes over 1k revs. STFT and LTFT return to normal, both about +/- 6 (when one is + the other is - , cancelling each other out)

This screams vacuum leak to me, but I just can't find it. I just had it smoked with an automotive tester by a diagnostic technician and it gave away nothing. We then attached it to the exhaust, nothing. Four cans and a squirty bottle of brake cleaner later, no change in revs. Soapy water in Open Loop mode, nothing. What else could it be?

An auto-electrician tested the new fuel pump, says it drops 0.2v and is perfectly within parameters. He says engine vacuum is fine too, pulls more than other cars its age (This version has a MAP sensor)

It has a new cat. conv., throttle position sensor, fuel pump (Pierburg, not a cheap one), fuel filter, fuel injectors pulled and tested, NGK spark plugs as they are gapped to 1mm, both 02 sensors have been replaced (the rear one is from a parts store, the front is from eBay using the ford part number) HT/Ignition leads are new.

Any ideas? Thanks in advance.

Waseem


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Old 07-31-2016, 06:28 PM   #2
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Moved to General Tech Chat, Zetec Performance is for Performance modification questions whiloe this area is for most DIY repair questions.

Now for some more reading/thinking....
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Old 07-31-2016, 06:36 PM   #3
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Lean running isn't going to make the fuel pump randomly cut out, sounds like a problem in that system despite the new pump/filter.

What's really a question is why fuel pressure wasn't tested, that's where you see if there is a problem there not by electrical testing of the pump itself. Scan tool can give a pressure read out, don't have to make up a fitting for a mechanical gauge.

OK at idle and lean over 1k RPM might also point to a lack of fuel pressure as it demands more.

Was the entire module replaced or just the pump?
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Old 08-01-2016, 04:21 AM   #4
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It was both the Fuel Pump and the Sender unit as they come as one assembly. It's lean at idle and the numbers run fine when you give it any gas. Fuel filter was free of any sludge but I replaced anyway. I'll get my diagnostics man to pull some fuel pressure numbers to share with you as my OBD II doesn't have that.
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