another FI vanagon question

[ruslandobrovensk@hotmail.]

Hi all,
this is my first post on this forum. I recently came across 88 vanagon GL 2.1L with stick shift. van seemed useful for my purposes so decided to get it . paid $500. vanagon shows it age but seems more or less sound , someone before me had changed the engine.. But it has electrical running issues. I read so much about it on this forum... To make long story short engine looses power and doesn't rev above 3-3.5 rpm when it warmed up, just in 2minutes after initial warm-up ECU cycle completes.

I read all possible posts on this forum about possible causes...

so far I changed: cap , rotor , fuel filter, O2 sensor (from GOWESTY) , Temp2 sensor , I got 2 other used AMF in working condition, got another used ECU from 1991
Checked and cleaned all the grounds , did all tests according to wire diagram
Checked compression 130-140--130-140 psi.
Checked fuel pressue tests: about 30 psi (I cant say exactly , my gauge is 200 psi max.) looks like pressure regulator holds pressue, spray patterns looks like a cone
All in all it looks normal.. I can't find any explicit problems ..

So my current problem is this:
in desperation I replaced the coolant temp sensor with variable potentiometer 0-10 Kohms an installed the ECU from 1991 van. It came out that if potentiometer has resistance about 1-1.3 Kohms engine runs very good. (revs to 5K rpm , seems has power, ) so I left this potentiometer in place for the last 2 weeks. looks like now my vanagon runs pretty good (I drive about 150-200 miles per day , highways , I get 16.5-17 MPG all the time ) so far I drove it like that for last 2000 miles .
Yesterday I tried to pass NJ inspection and of cause did not pass it. my CO2 level is 2.05% instead of 1.67%.
Honestly I am confused now. If I hook the original Temp2 sensor back , engine just refuses to run normally ?

... any ideas on this ? thanks you

[tencentlife]

Seems like you've checked out a lot of things. Did you check wiring at ECU plug with sensors in place, so you're taking account of their connections, too? Many is the time someone rings out the wiring OK, and sensors test as normal in isolation, but the connections add resistance or connect intermittently and cause trouble.

Did you test the Intake Air Sensor in the AFM?

Set the timing?

Have you tried the late ECU in it yet? The part number may have a different last letter, but if the 9-digit number is the same you can swap it in. There is one model, I'm pretty sure ending in "F", that has a higher rpm limit than the "D" models. Sometimes the "F" one doesn't have VW P/N on it, only the Bosch P/N.
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[stevey88]

I am no expert in WBX engine but it seems to me by varying the resistance of temp2 sensor, you are varying the mixture as the ECU will allow a given amount of fuel to the engine based on the rev, temperature of the engine ( temp 2 ), air flow ( from AFM ) and intake air temp ( also from AFM ).

My question is does the resistance of the external pot you added needs to be lower when the engine is fully warmed up ? Can you vary the air temp senor resistance in the AFM like you did for temp 2 sensor to see if that make any difference ?
I am assuming you put the pot in the engine side of the wiring so you can confirm the wiring is good if there is a change in engine behavior.
_________________
Steve

87 Westfalia full camper 4 speed

[tencentlife]

The Temp2 and IAT are NTC thermistors, same as used on all kinds of cars (most of them have exactly the same curves, too, which means you can swap a lot of different makes of sender in place of the OEM if you wanted to). Adding more resistance to Temp2 tells the ECU the engine is colder.

But according to the ProTraining literature Temp2 is watched for warmup info and regulates warmup enrichment and determines when the O2 sensor signal gets integrated. Once a certain temp threshhold is crossed the ECU enters normal warm-running mode and Temp2 is not a determinant of actual mixture. It also helps regulate timing during warmup, but once warm timing is determined solely by rpm and load/IAT. If you take ProTraining at its word, Temp2 is pretty much not involved once the temp threshhold is crossed, and in normal running mode it only serves to tell the ECU whether or not to stay in that mode.

So adding resistance to the Temp2 circuit, depending on how much, would force the ECU back into warmup mode. In warmup mode the O2 signal is being ignored, and timing and mixture regulation once again has a lot to do with the Temp2 resistance.

So what I'm wondering is what that is masking. There is some bad signal present once in normal mode that is ignored during warmup.

So, I'm thinking IAT and O2, and to be sure there's no grounding in the O2 signal cable. And to be sure timing is right since the timing patterns change between warmup and normal mode.
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Please don't PM here, I will not reply.

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[ruslandobrovensk@hotmail.]

Just had some tinkering session with my van today.
if I connect Temp2 sensor back to ECU engine starts to cut out after 3.5k-4K rpm . looks like a bad ignition wires or "bad AMF syndrome" (loss of power, no revs.., rough idling)

I checked and adjusted TPS . it works as it suppossed to .... If I fully depress the gas pedal I feel like engine starts to pull .. but only in range of 4.5K to 5K rpm.
Dash temp gauge needle stays almost in the middle , just below the light .
I disconnected the ECU and checked Temp2 resistance between 6 and 10 terminals and ohmmeter showed 0.38 - 0.4 Kohms. and resistance was increasing with engine was cooling down: 0.54 .. to resistance 0.98 kohms matched to the needle stayed on the edge of white sector ..
ECU change makes no difference. my old unit is 0261 200 065
and the "new" one is 0261 200 284/285

After that I hooked my variable potentiometer back in place (instead of Temp2 sensor ). Brand new O2 sensor was connected as well.
I got the same result with resistance 1.0 - 1.2 kohms engine works just fine: smooth idle and good acceleration to 5K rpm; there is no intermittent loss of power , warm engine starts right up...
Like nothing has happened and all bad symptoms are gone...
I realize that it is not normal... but what exactly?

[ruslandobrovensk@hotmail.]

just to add that I been riding my van with potentiometer in place for the last 2 weeks and 2K miles engine works just fine . 4000 rpm - 70 mph
good acceleration . 16-17 MPG at 50-70 mph. I noticed that when the ambient temp goes up acceleration is slightly slower and it takes a bit more cranking to start the engine. Also I put potentiometer next to drivers seat. to play with it on while driving. I noticed that you can decrease the resistance very slowly when engine is warmed up to 0.5kohms but all over sudden I may start to experience power cut off . until I return back to 1.0 kohms . but again it is king of tricky : I need to turn the engine off , set 1.1 kohms , start engine and it runs just fine after that.
looks like that ECU is very " picky" about abrupt increase of resistance.

I understand that the problem lies somewhere else but where ?

I did fuel pump volume test : 900cc per 30 secs, checked the pressure (30 psi and increases to 33 psi with vacuum line off ), and it holds pressure for the next 10 minutes just fine , Injectors have a cone shaped spray ... but seems like cone is a bit "thin" to me .
I did not change ignition wires yet but again with my potentiometer in place engine seems to run nice , 900 rpm idle (however my idle control system is not working) and smooth acceleration in all range .

[tencentlife]

When you add resistance to the Temp2 circuit, the engine wil enrich mixture, thinking the engine is cold, s it makes sense that when the engine is actually warm that there is some point where more resistance there makes it run poorly.

One thing the ECU is NOT looking at when you add that resistance to Temp2 is the O2 signal circuit. We've learned here that it is fairly common to find damage to the green coax wire that carrries the O2 signal. If the center signal wire is shorting to ground at all the thing will run really badly once the temp threshhold is crossed, the most notable symptom being that it runs pig-rich. You check it by disconnecting the O2 sensor and the ECU, and making sure under those conditions the center signal wire is isolated from ground. The noise-suppression sheathing around the coax has to be common to ground. The grounding often happens at the end of the coax if the sheathing braid wires can contact the sensor connector, so take a close look there.

IAT sensor also has more input to both mixture and ignition timing once it has crossed the warmup threshhold, so test that circuit at the ECU connector as well. I haven't seen you mention that.
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Please don't PM here, I will not reply.

Experience is kryptonite to doctrine.

[crazyvwvanman]

First thing I will say is keep in mind that the problem may be caused by something that you can't fix by swapping parts!

The ECU watches the Temp2 sensor and as the engine warms up a point is reached where the ECU sees a warm enough engine that it switches modes and tries to use the O2 sensor feedback to adjust the mixture. Your bypassing the Temp2 with a resistor is just telling the ECU that the engine never warmed up. This causes the ECU to keep ignoring the O2 sensor reading and keep using the set programed values for the fuel mixture control.

The O2 sensor SYSTEM WIRING is an extremely common problem area. That wiring is made up of 2 main parts. The sensor signal wire and the sensor ground reference wire. The green O2 wire coming from the ECU wiring is a coax cable. The signal wire is in the center and an insulated shielding wire braid surrounds it. The shielding wire must not make contact with the center signal wire. Also the shielding wire must be grounded properly. This ground is provided by a brown wire that is tied to the shield inside the harness and then the other end of this brown wire comes out of the harness with the small bundle that goes to the distributor hall wiring. This brown wire must be screwed down to the engine and you should check for this.

There are simple ohm meter tests you can perform to check that this O2 wiring is in reasonable order. If you are willing and able to perform these test there are people here who can describe how.

Mark

[stevey88]

[ruslandobrovensk@hotmail.]

I checked that 02 sensor green wire as well . I made sure that external shield is not in contact with signal wire .. Probably I need to do it again and more carefully...
couple of weeks ago I tested it for continuity with ECU hardness and against ground . did not find anything ... I remember I initially disconnected o2 sensor and engine started running better so I concluded that 02 is bad so I I bought that Bosch universal type from busdepot .. engine ran bad again. so I bit the bullet and bought the $130 bosch 02 sensor from gowesty. engine started to run better (at least smoother) but not exactly right ... crazyvwvanman mentioned that braid shield should be grounded tho the engine ??!! I did not see any brown wire connected to the engine !! could it be a cause ? I also read somewhere on this forum that engine left head should be grounded as well ? if so is it applicable to 2.1 L engine , I did not notice any specific ground wire on left head .. I replaced one braided ground wire from engine block to (left side ) to ground screw under the ignition coil ? Yes, I noticed that with my " pig-rich" mode seems like the ECU is not responsive to o2 sensor ( I see no effect at all if I ground the cignal wire )
I guess I need to check this o2 green wire again

[tencentlife]