AFC fuel injection 1977 Beetle

I checked the OHMS of the number 2 temp sensor as specified by the maintenance manual. Bentley Manual. It was reading around 7,000 OHMS when it should of been around 2,500 OHMS. So I ordered a new sensor from Aircooled.net I installed it last night and as I suspected the car ran rough so I had to re-adjust the air/fuel ratio by the adjustment screw under the air box. I adjusted it to full rich I believe and it still was not enough. The box had been opened before so I suspect the whole air flow meter needs to be opened again and re- adjusted. I just don't know how exactly.

My other question is this. When I took the old sensor off. It had this adapter on the end of it that goes between the sensor and the engine head. It plugs in right between just like an electrical adapter but the ends of it are the same as the sensor and the port that it goes into. It looks like the end of a chisel without the wedge part as it's long but it just plugs in between the two. Do I need that part on there? I couldn't separate them so I put the new one on without it and it fits fine. The old part had a lot of rust on it which could of been the reason why there was more resistance than usual. What does this part do? Why is it there?

Reply to
eastwardbound2003
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Ignore the adapter; not needed.

The adj screw only makes very tiny changes to the ratio and would only be noticeable around idle speed.

If the box has been tampered with, who knows what was done. You can pry the cover off and then gently move the resistance wiper arm with the engine running. That will produce very big ratio changes so you can see the effect.

It's possible that the spring tension on the wiper is out of calibration causing the error. Or the carbon resistance paths could be worn out.

Also note that small air leaks anywhere in the induction system will create errors that the AFM can't correct for.

Go to:

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Click on Library. Click on "F" for Fuel Injection.

Atwell has several articles about the FI that may help. He has researched the temp sensor carefully and reports on it too.

Speedy Jim

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Reply to
Speedy Jim

OK help refresh my memory. Are you talking about the cylinder head temperature sensor? Located around on the left cylinder head? Corrosion is NOT a friend when it comes to sensors especially that one! ;-)

The engine was running too lean? Are you sure? How can you tell? Like Speedy Jim said.......vacuum leaks! Check the intake manifold boots and all other possible vacuum leaks especially the large boot since sometimes the smaller hose might pop out of it. I think that there is a plug that might pop out of the "throttle body" too if there was heavy popping in the intake manifold.

Were you turning the Air Flow Box adjusting screw Clockwise? Check it's flap too since it might have a plug/cap that might pop off too or the flap could be twisted.

Are all of the injectors firing? Are all of the spark plugs firing? Does the engine have all cylinders developing power?

I know that the Type 3s can get their fuel pressure adjusted up or down. I think with the Type 1s there might be a vacuum lead to a solenoid that might raise fuel pressure when the vacuum drops.

It has been too long since I have had to "dive" into troubleshooting one of these. Maybe a fuel pump relay lately and that was too easy.

BTW......PLEASE ALWAYS CHECK THOSE FUEL HOSES AND REPLACE THEM PERIODICALLY!!

Reply to
dave AKA vwdoc1

Dave is correct; there is a fuel pressure regulator, controlled by vacuum. Do the pressure measurement spelled out in Bentley.

Jim

Reply to
Speedy Jim

I just wanted to update everyone on what happened to this car. I troubleshooted the problem with the number 2 temperature sensor with my trusty multi-meter. I then found out that the problem was not the sensor but was something with the wiring harness giving out 3,000 OHMS resistance on its own. I further traced the problem using a 10 foot long 22 gauge wire going from the lead for the temp. sensor in the engine compartment and all the way back towards where the wiring harness plugs into the computer for the fuel injection. I was trying to find out if there was a cold spot in the wiring harness causing this 3,000 OHM resistance. To my surprise the wiring harness only had a 1 OHM resistance and there was actually nothing wrong at all with the engine wiring harness. The whole time I had a faulty computer/ brain/power-train control module (PCM) whatever you want to call it.

Unfortunately I can not find anyone who sells a new or re-manufactured computer for this car. Not mid-america motorworks, not JC Whitney or anybody else what have you. This is quite disconcerting for me. And I can't just put in a brand new 1600cc dual port w/solex carb because it all has to be CA smog legal. What a rotten day on the west coast, especially with all this smoke and ash from the wild fires!

Reply to
eastwardbound2003

Do a search on:

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"ECU"

I'm a little confused though where the 3000 Ohm error was. And how you know for sure the ECU is bad. ? Speedy Jim

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Reply to
Speedy Jim

These almost sound like your situation and Speedy's responses! lol

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is it you!!! 8^) try contacting
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"should" be a breeze for them if they want to touch it! ;-) Now how do you "know" that is not normal for that circuit? I would think that circuirt would inherently have some resistance using a low impedence DIGITAL VOM coming from the ECM. On some vehicles I am able to check wiring, sensors and other components from the ECM's harness plug. So did you read that circuit with the cyl head temp sensor at the ECM plug?

Reply to
dave AKA vwdoc1

Yes, what I did was check the circuit at the ECU's plug using a wire running from the back seat to the engine compartment. Essentially the currently only passed through the wire on the engine harness just for temp. sensor #2 including the 10 feet of wire I bought from radio shack. The two lengths of wires together had 1.2 OHMs. But If I check the OHMs with the ECU attached and from the engine compartment, it has an extra 3,000 OHMs tacked on to it. Troubleshooting does take time but at least now I can eliminate the sensor and the wiring harness as the culprit which can only mean that the problem is the ECU. The car still runs, but gets terrible gas mileage and has poor performance.

East-

Reply to
eastwardbound2003

lol

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>OR is it you!!! 8^)>>

I know I'll sound like I'm beating a dead horse or badgering, but I'm not convinced that the ECU is at fault. And, if it were my car, I'd want to know for sure before forking over a chunk of change for another box.

You said: "check the OHMs with the ECU attached and from the engine compartment, it has an extra 3,000 OHMs tacked on to it. "

Does this mean that the temp sensor was disconnected and your multimeter was connected from chassis to the harness wire (the one that went to the sensor)? And the meter read some resistance that was 3,000 Ohms more than you expected?

If the above is what happened, then the reading may be perfectly normal. The resistance looking *into* the ECU has no meaning and has nothing to do with the temp sensor resistance.

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Want to do an experiment? Go back to Radio Snack and get some kind of variable resistance (like a volume control), if they have any. An ideal one would be something like 10,000 Ohms. Ground the center terminal to chassis and connect one of the outer terminals to the harness wire that normally connects to the temp sensor (we won't be using the sensor).

(Alternate: Get a handful of 1/2watt resistors, like:

100, 330, 470, 1K, 2.2K, 3.3K. One at a time, connect one of them from chassis to the harness wire.)

Get the engine running and turn the control thru its range. Does it affect the running? It may go all the way from purring smoothly to belching black soot.

If the control has any effect at all, the ECU is very likely working just the way it should.

Speedy Jim

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Reply to
Speedy Jim

tp://en.allexperts.com/q/Volkswagen-801/1979-Super-Beetle.htmhttp:/...

Jim, if what you are saying is true. Then that would mean that I tested the sensor the wrong way. I placed the multi-meter in "series" between the sensor and the engine wiring harness where it normally attaches. I did this according to the diagram in the Bentley manual where it displays the meter placed just like what I described with the sensor mounted on the engine block. One end of the meter attaches to the sensor and the other attaches to a symbol that looks like an "I" with a circle on top which to me would mean an electrical connector. If the meter was supposed to be grounded to the engine block it would show an electrical schematic symbol for "ground". So please bare with me here. What is the correct way to test the temp. sensor if I am doing it the wrong way?

If I attach the meter between the sensor and the other side of the meter grounded to the engine. It displays a healthy 2,500 OHMs.

Reply to
eastwardbound2003

Thanks for the help but this company does not appear to refurbish ECUs/ PCMs for air cooled VWs, only for certain water cooled Vee Dubs.

Reply to
eastwardbound2003

lol

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>>>OR is it you!!! 8^)>>

Ah! Mystery solved then.

That horizontal bar *is* the symbol for chassis earth in Euro-speak. Sensor is OK and, most likely, the ECU is OK too.

Time to look for another culprit...

Jim

Reply to
Speedy Jim

OK I was hoping that bba might! Did you call?

Usually when the engine is running really rich it is due to the air flow box. Flap could be jammed or the resistance inside could be bad. I think I used to take the plastic cover off and adjust them somehow but this was about 30 years ago and I just don't remember. These almost sound like your situation and Speedy's responses!

lol

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OR is it you!!! 8^)>

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It "should" be a breeze for them if they want to touch it! ;-) snip

Thanks for the help but this company does not appear to refurbish ECUs/ PCMs for air cooled VWs, only for certain water cooled Vee Dubs.

Reply to
dave AKA vwdoc1

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