andyturner

I suspect the emmisions from my S2 are suspect. When I start the car from cold it runs fine with no visible exhaust, after about 30 seconds the exhaust is visible and white smelling strongly. Has anyone experience of this. I have heard that when the fuel brain packs in it defaults to a rich setting, coud this be the case?

Andy

Rich9928p

The S2 (1984 - 1986 Euro - ROW) uses a 25 pin LH fuel injection controller. This device doesn't use the infamous hybrid chip that is part of the 35 pin LH fuel injection controller used in the 1987 - 1995 systems. The earlier LH failure symptoms tend to be age related failure of components such as power transistors, capacitors and ICs. Failing to a rich mixture would be much less common then with the 35 pin modules.

I suggest removing the Temp II sensor and checking the resistance readings across the temperature range, starting with ice water, tepid water, warm water and then hot water. Sometimes the failure mode includes a non-linear reading or open circuit that can throw the fuel injection off kilter.

If the Temp II sensor is OK, I'd next suspect the fuel pressure regulator. Pull the vacuum line and look for fuel running out of the vacuum fitting. If there is no leak, check the fuel pressure and see if the system holds pressure over time (all part of the test spec). If fuel pressure is not the problem, next look to the MAF.

Swap your unit out with a known good one (they're all the same, 1984 - 1995) and see what happens. The one difference is the 1987 - 1995 systems ignore the base CO setting adjustment at the MAF, so if you use a MAF from one of these 928s, it may not be adjusted for the optimal air - fuel ratio.

Only after these tests would I suspect the LH. If you like, I can recommend a company in your part of the world who could check out your LH for you.

Lorenfb

"The earlier LH failure symptoms tend to be age related failure of components such as power transistors, capacitors and ICs."

Not correct! The early LH 25 pin units are VERY reliable and rarely if ever fail.
They usually fail because of an improper troubleshooting procedure.
Furthermore, the semiconductors (transistors/I.C.s) used by Bosch have basically
a zero failure rate with other components used, e.g. resistors & capacitors, having
similar failure rates. Semiconductors generally don't have the "age effect" as do
mechanical devices, i.e. they usually have what is called an "infant mortality" failure
mode.

A better method for checking the temp sensor is to measure from
pin 2 of the LH unit to ground. That way the wiring and connections
are checked besides the sensor itself.

John Speake

It could be MAF failure Andy. Does the car run OK ? Is this "problem" recent ?

Have you meansured the exhaust CO ? Fuel consumption ?

Rich9928p

Lauren

I don't understand why you always must be so combative in your posts.

a. I didn't say that the 25 pin LHs were not reliable - however - some DO fail - THAT IS A FACT. The majority that I do test, however, test good.

b. Semiconductors and passive elements do have infant and age related failures - not all of them function forever. If a component fails after 20 years, I call that an age related failure.

c. I normally recommend as you said, check the Temp II sensor at the LH connector, however, in this case Andy has a COLD running issue and unless the ambient engine temperature is cold enough (i.e. ice water), he cannot check the resistance of the Temp II sensor at the lower temperature(s). IMHO, if there is a non-linearity problem it is best to test over a wide temperature range.

drnick

yeah, what they all said. if the car is basicaly running then there is unlikely to be anything wrong with the brain. i dont know about the temp 2 sensor but i do know that the MAF is more likely to be suspect if the car isnt running smoothly or making the power it should. john speake is able to test your MAF if your worried. if your concern is based on poor gas mileage which you are atributing to wasted fuel via the exhaust its more likely to simply be a normal healthy 928 appetite! have you seen the diesel conversion??

jeff jackson

I think the odor you are referring to is the "cold start enrichment" built in to the pre programmed fuel map, which is controlling the mixture (in a rich condition)...till the engine is fully warmed, and switches to 'feedback-O2 sensor" controlled management. Its not unusual for a cold started engine to run rich for the first few minutes...its designed to do this. The temp sensor 2...if it were the culprit, would prevent the engine from starting at all...if I'm not mistaken. If after warm up the odor fades, and the exhaust "normalizes"...things are working properly...if not, suspect an O2 sensor needing replacement, or perhaps a MAS or cat converter problem...

Rich9928p

Andy is from the UK, and it is unlikely that his S2 is fitted with a catalytic convirter or an O2 sensor. The Euro/ROW cars of this vintage ran open loop.

If the Temp II sensor is defective, and reports to the LH that the engine is cold when the engine is not cold, the engine would be running rich because the LH would indeed be providing an enriched fuel mixture.

jeff jackson

Thanks for pointing that out Rich...I have a "tendency" to assume everyone here is from the USA, and has US spec cars. I should have looked at his avatar to see otherwise. Thanks for clearing this up for me...

Lorenfb

The typical Porsche engine temp sensor will read about 2000 ohms with a cold
motor, and about 200 to 350 ohms warm. The temp sensor need not be removed
for the cold or warm tests. Both tests can be performed from the LH connector.