Strange Idling issue

[jcasey007]

symptoms are:

when first starting up after leaving it for about 5 hours, the idle is very low and erratic, but only before the Lambda sensor is up to temperature. If I immediatly switch to LPG the idle is fine (even though the Lambda is cold)

I know it is linked to a cold lambda as I have a realtime air/fuel ratio meter that shows when the lambda is up to temp.

The lumpyness on petrol only lasts about 20 seconds (until lambda is up to temp) and then it is fine, Hot starts are also fine and a restart with the engine still cold is fine once the lambda is up to temp the first time.

I can also force the engine to start on LPG again no idle problem from cold.

I assume the PCM has a default fueling map which it uses before it gets a realtime signal from the lambda (exactly the same as the LPG controller).

I've done the usual (clean MAF, disconnect battery for 10 mins) checked fuel pressure) it's been doing it for months and is a pain in the bum

It's got me stumped, any idea's?

cheers

Jim

[SB98UKexplorer]

you have 2 lambdas, maybe your reading the one? how old are the lambdas?

[jcasey007]

likley to be the originals (knowing my luck ) with 160k on them

I guess I could rig up a switch to be able to switch my display between the two. Am I correct in thinking they are both upstream of the Cats and the 97 did not have the downstream Lambdas.

worth checking out tomorrow, Thanks

cheers

Jim

[SB98UKexplorer]

as far as i know when i had my p reg 96 build explorer they where up stream and so has my 98

[jcasey007]

just been under her and yes only the two upstream, just identifying the signal cable for the near side sensor in the wiring diagram

I wonder if the NS sensor has been duff since I have owned the car as it's never been very happy on petrol (hence I use about £10 a month)

When crusing with a light throttle I get a surge effect which clears if I ease off or accelerate, I've changed what I thought was every thing (erg, Cam and crank, MAF, temp sensors) and gave up in the end.

I've just checked the wiring diagram and it is showing 3 Lambda sensors and not 2

[chrisquelch]

you should remember most wiring diagrams etc are for u.s. models and there are slight differences on UK cars. cheers chris

[jcasey007]

I found a very good post

http://www.explorerforum.com/forums/...ghlight=lambda


on Start-up the section in red below indicates exactly when the issue happens in open loop

Open Loop or Closed Loop?

An engineer will tell you that a system which uses output feedback to control its operation is considered a “closed loop” system. One which does not is “open loop”. We know that an O2 sensor runs on heat. An engine in startup does not produce enough heat to make them work. SO…. On startup, the engine computer fuel system runs in “open loop”… and utilizes stored information to provide fuel metering. Once the O2 sensors get warm enough to start operating, the system switches over the them, and into “closed loop”. Starting in the mid 90’s we added heaters to the sensors to speed up this process, since closed loop was friendlier to emissions. Thus the Exhaust Gas Oxygen Sensor, or EGO sensor became “heated” and is now called the Heated Exhaust Gas Oxygen sensor or HEGO sensor. When people see HEGO sometimes they get all confused. It is just the Oxygen Sensor, with heat. Heated sensors usually have 4 wires, non heated 1 or 2.

[jcasey007]

I Managed to test the Lambda's today, both read the same on start up (very low voltage of about 0.1 volts which is expected acording to the specs.

So still no further forward, any tests are slow as after every start I have to wait over 4 hours before I can test again

Guess I will have to live with it

cheers

Jim

[kevin p]

Hi Jim, if you didn't have gas, its got all the symptoms of inlet gaskets leaking.
I don't know the ins and outs of running gas, but does running on gas perhaps not be so critical on the ammount of air being taken in? [ it has been mentioned the maf dosn't work on gas]

Just a stab!

Kev.

[jcasey007]

I did all the manifold seals 2 weeks ago, and yes if the symptoms disapeared when the engine gets warm I would agree but it looks to be linked to the default fueling map (or something)

[SB98UKexplorer]

since you have been changing parts have you reset the ecu after that?

[jcasey007]

yes battery disconnected for an hour last week, no change next morning