P0171 code, low idle and loss of power

[stuRS]

Hi guys,

 

Bit of background - my 2003 JDM has recently had a new engine fitted by me (with some help from R55LEE). New engine is a 44k mile UK DE lump.

 

Since the new engine went in it's been running badly with CEL light on and I've tried a few things but no joy yet. Symtoms are:

 

* Low idle causing engine/gearbox vibrations

* Constant RPM or speed causes loss of power, most noticable at 2500 revs

* When I apply heavy throttle i.e. when accelerating it runs fine, it will also correct itself if I come off throttle and reapply (sometimes)

* I cannot hold the engine at 2500 revs, it either climbs above or drops below, apart from when I removed the Pop Charger filter when stationary, it seemed to run better and hold constant 2500 revs then

 

I've done the 'pedal dance' which gave me P0171 fuel bank 1 lean - Having read the service manual, this points to HO2S1 (upper O2 sensor - drivers side)

 

I've fitted a new Lambda, the HO2S2 (lower O2 sensor) from ZMANALEX, I thought I'd ordered the right one from Alex but a lower sensor turned up but having got under the car when fitting, I noticed the HO2S1 sensor is on the manifold, which came on the new engine, so I can't see that being damaged...Alex - my mistake not yours so don't worry - no hard feelings there.

 

So my current logic is this:

 

The cats would have had a fair amount of fuel/oil/coolant pass through them when the old engine went bang, so I think they could be buggered. I've bought a set of Decats to see if the cats are causing problems on the basis that I can run them for a while and flog them at relatively little expense.

 

I've checked the Induction system, which is a JWT Pop Charger. I re-oiled it when doing the engine fit but can't see this causing the problem. The MAF seems clean and clear, and I have no error code relating to MAF issues.

 

Other than a leak on the plenum gaskets I can't think how it's leaking air - the idle is low too (after it's ran for 20-30secs) which leads me to believe it's a sensor to ECU related issue.

 

If anyone can suggest possible causes or if anyone has had the same issue I'd love to know about it, it's driving me mad! My car is JDM and therefore doesn't work on my OBD11 reader.

 

I would be particularly interested in another with knowledge of sensor to ECU timings e.g. why it's constant revs that causes loss of power and why the idle drops after a set time. It would have to be a major induction leak for it to effect idle I would have thought.

 

Thanks,

 

Stu

[ZMANALEX]

After reading the above my guess is that you are running with wide band front O2 sensors which came in the manifolds with the UK engine.

I reckon that your JDM should have non wide band sensors and this may be your issue.

Swop over the front sensors from your old engine and see if this cures your problem.

 

Alex

[stuRS]

Hi Alex,

 

That's very promising! So you think running a JDM car on UK upper sensors would cause this?

 

What is the difference between UK & JDM sensors? Also - I'm only getting Bank 1 lean, wouldn't the UK sensors do both banks?

 

Final question - have you got any in stock? Lee's got my old engine and I haven't been able to get hold of him for 2 weeks

[ZMANALEX]

Hi Alex,

 

That's very promising! So you think running a JDM car on UK upper sensors would cause this?

 

What is the difference between UK & JDM sensors? Also - I'm only getting Bank 1 lean, wouldn't the UK sensors do both banks?

 

Final question - have you got any in stock? Lee's got my old engine and I haven't been able to get hold of him for 2 weeks

 

Best to get your old sensors back and try them as that would be the cheapest option.