Re: 1996 Golf Mass air flow sensors

OK, I don't know. I'm asking.

Does this VR6 have a distributor, or is it all taken care of in the coil pack? Never seen one, just saved the post from Chris since it seems to have been historically helpful.

Mark '95 Jetta GLS (the 2.0l kind)

CTS (Coolant Temperature Sensor for the fuel injection) check with an Ohm meter

I don't think the mass air flow sensor really comes into play during the starting phase. Think about it, "Mass Air FLOW Sensor". If your car isn't moving, the air flow is zero, so its unlikely that the ECU is getting a disruptive signal from this component. It sounds like the engine isn't getting fuel when things are cold. The other possibility is that the distributor or it Hall-effect sensor might have temperature dependencies.

Here's an idea: Buy an engine scanner and check for codes generated during this hard-to-start phase when the engine is cold, or take it to a mechanic and have them do it. It may not be storing trouble codes, but they may be appearing during run time.

: I don't think the mass air flow sensor really comes into play during the : starting phase. Think about it, "Mass Air FLOW Sensor". If your car isn't : moving, the air flow is zero, so its unlikely that the ECU is getting a : disruptive signal from this component.

Pardon me for intruding here but .... what does the motion of the vehicle have to do with the flow of air which is being sucked into the engine when it is being cranked by the starter ?? (I think that someone was about 3/4 asleep when that statement was written??)

: It sounds like the engine isn't : getting fuel when things are cold. The other possibility is that the : distributor or it Hall-effect sensor might have temperature dependencies.

: Here's an idea: Buy an engine scanner and check for codes generated during : this hard-to-start phase when the engine is cold, or take it to a mechanic : and have them do it. It may not be storing trouble codes, but they may be : appearing during run time.

-- benf-at-chebucto-dot-ca (make the obvious changes to reply) **************************************************************** What future can there be for a society that values entertainment more highly than education? Ben Fullerton 1996 ****************************************************************

Nothing.

But when the vehicle's ENGINE starts, there's basically no air flow into it. Sure, cranking the starter pulls in some air but it's not considered the same as when the engine runs.

When starting the engine, the control computer runs "open loop" since:

1) The oxygen sensor isn't hot yet. I don't think even the self heated ones come up that quickly. 2) The MAF sensor also has to heat up.

When the engine warms a bit, the controller goes into closed loop mode, using the oxygen sensor, MAF sensor, etc, etc...

Other times the engine can be running open loop (not using the signals from the oxygen and MAF sensors, et al) are when the computer detects a bad sensor. Instead of using what looks like bad data, it goes to a default, or 'limp home' mode. This should set the error flag and turn on the "check engine" light.

Mark '95 Jetta GLS

Mark Randol ( snipped-for-privacy@austin.rr.com) wrote: : In article , snipped-for-privacy@chebucto.ns.ca says... : > Pardon me for intruding here but .... : > what does the motion of the vehicle have to do with the flow of air which : > is being sucked into the engine when it is being cranked by the starter ?? : > (I think that someone was about 3/4 asleep when that statement was : > written??)

: Nothing.

: But when the vehicle's ENGINE starts, there's basically no air flow into : it. Sure, cranking the starter pulls in some air but it's not : considered the same as when the engine runs.

I think we are disagreeing on semantics here more than air flow??

Assuming a cranking speed of, say, 200 rpm (I know of some that crank at higher speeds on the starter) then the air flow would be about 1/4 that of the airflow at an idle of 800 rpm. I would hardly describe this as "basically no sir flow" - but agree that it is small enough to sort of justify your perspective. :-)

However, if "open loop" totally ignores air flow, then blaming a defective air flow sensor for a 'no start' might seem to be the wrong place to look.

: When starting the engine, the control computer runs "open loop" since:

: 1) The oxygen sensor isn't hot yet. I don't think even the self heated : ones come up that quickly.

: 2) The MAF sensor also has to heat up.

Assuming MAF = Manifold Air Flow, what does that have to do with temperature - or are you referring to the air temp. sensor that also lives in the same shell as the MAF sensor? (Remember - it is my first VW, and I am still trying to learn to speak the language.) With an extensive background in temperature measurement - from 0 Kelvin to over 3,000 C - I can think of only one temperature measuring device that requires heating. It is definitely NOT the type that could be used in this application. The others are all heated by the material being measured.

: When the engine warms a bit, the controller goes into closed loop mode, : using the oxygen sensor, MAF sensor, etc, etc...

Does the "Bentley" repro. of the original VW manual have a list somewhere of the sensors used in 'open loop' and 'closed loop'? I would really like to see such lists!

: Other times the engine can be running open loop (not using the signals : from the oxygen and MAF sensors, et al) are when the computer detects a : bad sensor. Instead of using what looks like bad data, it goes to a : default, or 'limp home' mode. This should set the error flag and turn : on the "check engine" light.

If you, or anyone else is still with me here, I have a problem of my own that I could use some expert VW help with. :-)

1984 Vanagon "Westfalia": Fuel injection, AFC System, Water cooled, Digijet.

Poor starting when cold all summer - and, now that the colder weather is here, no sign of life at all when it is cranking over on a fully charged battery.

In the summer, and when cold, the light at the top of the (Temp. gauge I think - or maybe fuel gauge?) panel would flash steadily about 20 times. Then the engine *might start .... or might not.

Now, October in Nova Scotia, temperatures from mid single digits C to mid teens C, the flashing does not stop and there is no sign of life when cranked over.

Once started it ran reliably, if not well, until the next time it cooled off for several hours.

The previous owner (NO significant motor vehicle knowledge) told me that it had been diagnosed as *probably the air flow sensor. (It tests well within specs.)

Following the last time I had it running (about three minutes of idle plus a few shots up to about 2500 rpm) the spark plugs were found to have a generous coating of dry, fuzzy black soot - ie improperly burned fuel (incomplete combustion).

So far, I have been spending most of my diagnostic time studying the manual - and finding nothing that has been of any real help ... so far.

: Mark : '95 Jetta GLS

Any suggestions would be appreciated.

Ben F.

============================================================= Certified mechanic, British Sports Car Specialist since 1954. Jaguar Service Dealer 1959 -'66. Current British fleet: 1974 MGB, 1966 Jaguar 3.8 MkII Past: 9 MGs, 6 Jaguars, 23+ other British cars + 1955 Norton ============================================================= [Honorable mention: 1984 VW Vanagon Westfalia] Also: 1966, 27 yrs with Dalhousie University, Dept of Physics 1993, retired as Physics Research Technologist II 1996, bought my current Jaguar.