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Thread: Fuel Injection Troubleshooting with Volt/Ohmmeter

  1. #1
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    oved the connector to be sure the injectors were on the correct cylinder #s based on the pins being tested i.e. 11 & 7 being injector connector for cylinder #4. In doing this I found the injector connectors for cylinder #1 and #2 were reversed. Would this have adverse affects? I've been getting extremely poor gas mileage, 10mpg!

    By the way, where exactly in the Bentley does it mention the VW numbering of cylinders? I asked a local shop near me for the locations.

    Thanks for your help in advance.
    Last edited by Capt. Mike; 11-16-2008 at 12:34 PM.

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    What year and model?

    Suggest you change your preferences to allow email; without it you can't be contacted for further info or if needed during housekeeping edits/cuts/moves.

    Most temperature senders can be removed and bench tested with warm water. Using a quality thermometer, insert the sensor part of the unit in cold water and slowly heat on a stove, recording ohms at various temperatures. Avoid immersing the electrical connections. You might have to rig a temporary holder of baling wire or scrap sheet metal.

    Regardless of model & year, a reversed FI sequence at the injectors will cause both poor running & poor mileage. Some of the effects of wrong fuel injection timing are disguised in a manifold injection system such as used by VW because the fuel is not injected directly into the cylinder, thus the spray of fuel/air mixture is still around in the manifold when the valve does open and the mixture can enter the cylinder. Only now it's no longer the correct mix and timing so the resultant firing is inefficient. Usually there are some backfire or afterfire effects along with rough running.

    VW cylinders are numbered in accordance with what is pretty much the industry standard. #1 is RF on an air-cooled, water-cooled boxer, or the Eurovan V-6; the most forward in an in-line diesel or 5-cylinder Eurovan.

    #2 is RR on a horizontally opposed; #3 LF, #4 LR. #2 is the next back on an in-line engine. This arrangement is given in the Type II manual Section 5-11.9. I notice I've added a hand-written note in the Vanagon manual margin, so it is probably not given or at least in some logical location.

    With the change in manuals starting with the Vanagon, it "has been developed primarily with the professional automotoive technician in mind." Thus the elimination of a lot of general knowledge sections and step-by-step instructions for us amatuers. Too bad, we can all use a reminder now & then.
    Last edited by Capt. Mike; 11-16-2008 at 12:34 PM.

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    Thanks for the info. Especially with the fuel injector wires being crossed. I was told by a supposedly knowledgeable individual that it didn't matter. I thought it seemed odd that they could be interchanged. Next time I will get a second opinion!

    Thanks for the reassurance on the cylinder numbering. For some one who is relatively new at working on engines it can be deceiving to see plug wires crossed for the #1 and #2 cylinders. Intuitively you would think the distributor posts and wires would line up with cylinder. Not the case! In order to get the 1-4-3-2 firing order you need to cross the wires for the #1 and #2 cylinders. A good way to remember is if you turned the distributor counter clockwise it would be 1-2-3-4.

    Now knowing the year and model!
    Fuel Injectors. Spec approx.16-16.4ohm. Results varied a little with some reading 17.0 and others 17.8. I cleaned the connections and was able to get a reading of 17.0 across all injectors. Is 17.0 approx. enough?

    Thanks again

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    Thanks for editing your original post to include year and model. My answer below was predicated on an AFC system per the original title.

    A little understanding of the FI systems helps. There are two basic types -- mechanic and electronic. Diesels and some early gas were mechanical. Run off of gears, chains or belts. They literally have an individual pump for each cylinder. Electronic injection utilizes a pressurized fuel system that is triggered by a computer.

    Within each system, you can have direct injection (literally right into the cylinder like VW's TDI diesel) or manifold injection, where the fuel is injected into the air stream in the intake manifold to be sucked into the cylinder when the valve opens on the intake stroke. VW's AFC, Digijet & Digifant use the latter.

    However, the fuel is injected close to the respective cylinder so although the manifold may have a "charge", it can't pull it from end of one manifold pipe back into another with any efficiency.

    To compound, and may also be one of your problems, is there is a cold-start valve (injector) that adds fuel to the air-stream early to enrich it for all cylinders. A leaking cold start valve would drastically cut mileage. This valve is only supposed to operate on a cold engine and cut out as soon as it reaches minimum operating temperature. It is controlled by the Temp Sender II

    I would assume the injector resistance of 17.0 ohms to be satisfactory. The few extra 10ths of ohm difference could well be aging of wires and even meter or meter leads. That they are all identical and consistent shows them not defective. They are, in effect, electromagnetic valves and there should be enough voltage to activate them.

    FYI, your distributor, with the cap off, has a notch or cut in the rim of the bowl. That notch is also #1, so when the rotor is pointed to it, #1 is at TDC. Thus the continued rotation in 90° increments is your firing order. The distributor turns at one half engine revolutions.

    That VW's distributor is upright and terminals are arranged similar to cylinder layout is pure coincidence. Distributors are placed where they can get access to a crank or cam for drive gears and thus could be sideways or in any position on the engine. Many newer engines have two and some caps are internally arranged so all the wires come out the same side. The more complex firing orders like V-8's & V-12's start to look like spaghetti and thus labeling the wires is never a bad idea. Several companies sell wire numbering sticker kits.

    Your observation that in reverse rotation, the engine is in 1-2-3-4 order is noted in the same Type II Bentley section for adjusting valves. I don't like to turn my engine counter-clockwise, so adjust valves in the correct 1-4-3-2 order, but it can be done in the reverse. In actuality, most engines can have valves adjusted in just two or three crankshaft positions because various intakes & exhausts are closed during other parts of the cycle besides just at TDC, but I find it too complicated to keep track of and adds a risk of misadjusting one that may be just opening or almost closed, causing a burned valve or worse. Some short cuts aren't worth it.
    Last edited by Capt. Mike; 11-16-2008 at 12:34 PM.

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    >In the Digijet FI there is an Auxiliary air regulator that took the place of the cold-start value used on the air cooled engines. I performed the test described in the Bentley 24.28. The test checked out that it is working properly.

    Thanks for responding to my previous posts. Your knowledge is greatly appreciated. Being new to engine mechanics and trying to decipher the Bentley is often challenging.
    Last edited by Capt. Mike; 11-16-2008 at 12:34 PM.

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    Transferred from another post to consolidate similar topics.

    86+ Digifant information

    ben Member # 671 posted 07-09-2001 01:16 AM

    Here is a good site that everybody who is not afraid of using a voltmeter should know about, I don't know who is the guy but he knows is stuff, http://www.loam.org/vw/Vanagon/

    Many good printable sheet about checking and maintaining the electrical part of your Westy. I did print all of the "Digifant" pages, about 50, this is probably a add-on for mechanic, very easy to follow. It talk about the Vanagon syndrome to. Any amateur or advance mechanic should get those pages printed.

    Regards, Ben

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    I just purchased a volt-ohmmeter and have been using it to troubleshoot the FI system on my 1982 air cooled Westy. I have pulled the Temp II sensor and attempted to bench test it at various temperatures using a thermometer and hot water as Capt. Mike has suggested (see above). I had a very difficult time getting a stable resistance measurement, although I had stable readings when it was still installed in the vehicle. I suspect it is my ground connection. I had one end of the voltmeter attached to the wire coming from the temp sensor, and the other end grounded to the metal desk I was working on. Is this the correct way to bench test the sensor? Is a metal desk an innapropriate ground? Please forgive the naivete of this question. I am new at this stuff.

    Jake
    jake_beaulieu@yahoo.com
    jake
    [email]jake_beaulieu@yahoo.com[/email]

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    I'm glad to see at least one person actually reads what I write! Testing the sensor.

    No, you have to get more direct contact to the body of the sensor. What you have is probably the opposite of the corrossion problem mentioned in the Bentley pag 24.13. You've introducted an unstable ground connection. Although it's always a challenge to hold the sensor in the hot water without submerging the electrical connection, you will have to get a firm connection of the volt-ohmmeter ground to the sensor body.
    Last edited by Capt. Mike; 11-16-2008 at 12:35 PM.

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    In an off-site query, a member questioned his troubleshooting results. He was testing the relays per the Bentley on an '85 Digijet FI. Below is my response:

    Let's not make things more complicated than they have to be. Page 24.32 basically covers checking the relays on a Digijet so we're also talking the wiring diagram on pages 97.61-62, right?

    OK, in VW talk, terminal 30 is always the live supply power, i.e. the battery or "power in". It may be always live (fed from battery) or switched (power only with ignition on) but it's always the live supply. VW uses the very standard DIN relay numbering most of the time. Thus terminal 87 is the "power-out" terminal. Power in on 30 and then out to do its job on 87. Terminals 85 & 86 are the control circuit. They turn the relay on or off as the case may be.

    Relays can be tested independent of the vehicle. Take the relay to the bench with a 12v supply. 2 x 6v lantern batteries in series or a lawn & garden is plenty. Connect your ohmmeter between terminals 30 & 87. With power off (in this case) you should get infinity -- open circuit. Apply the 12v to the 85/86 set and the ohmmeter should go to near zero. This indicates the switch has closed and circuit complete. (All a relay is is an electric switch.) Look at the relay diagram in the wiring diagram. See how 85-86 control the electromagnet and 30-87 are the switched power set?

    If the relays are good, look at the wiring diagrams on 97.61-97.62. The right relay is commonly called the fuel pump relay. Notice 85 gets power from the ignition coil; thus it becomes live when the ignition switch is on. It then goes out 86 to the ECU #20. God only knows what goes on inside the ECU but we presume electronic controls have it complete the circuit so the relay operating circuit grounds and the 30-87 switch closes. With 30-87 closed, the fuel pump gets power and all 4 fuel injectors get power. They are now live and have fuel pressure.

    FI systems work on the principle that the fuel pump supplies excess pressure to the injectors at all times and the excess is bled back to the tank. With the pump on, you should have fuel into the injectors. The injectors are now an electronic valve that opens & closes the fuel supply to the engine.

    The left Power Supply Relay gets the same power on 85 but goes direct to ground out 86 so it closes the 30-87 switch immediately. 87 then feeds the ECU on terminal 13. Again, no telling what the hell is going on inside there but I suspect that's the power supply to operate the ECU. That there is a terminal 21 going out the other side of the ECU on the diagram is meaningless; anything could be happening inside.

    We will presume that the ECU is controlling the injectors in proper sequence by grounding them at the appropriate times. So the cycle is the injectors are live and pressurized, then the ECU allows them to open and inject fuel by completing the circuits in sequence.

    Since 86 comes out of the right relay (C) direct to the ECU, the Bentley warning not to connect a test light to terminal 86 is due to the fact that the test light will short out the ECU because the test light is grounded independently.

    With the ECU disconnected and your test light between 30 & 86, what you are testing is that 86 functions by completing the circuit to the ECU. Thus ECU is good or bad. They have you test the wire between the ECU 20 and 86 because they want you to be sure the failure is internal to the ECU, not along the wire.

    The 2nd test to terminal 87 just tests the relay, the step I suggested you simulate on the bench.

    The test of the injectors does show as testing between the two terminals in the wire. There's a better diagram on 24.56. Any test you can do with the light, can also be done with a voltmeter. You are testing to see if voltage occurs. Sometimes a voltmeter is better because it may show voltage but not enough to trip the light, thus you know something is grounding or siphoning it off. The ECU might be good but it's losing power along the path. Notice they switched to the more sensitive LED model by the time Digifant rolled around.

    Something to check out, 97.61 shows the aux air regulator feeding off the same connection that feed the injectors. Electricity takes the path of least resistance. If an aux. air regulator problem allows the voltage to ground out, the injectors may not be getting their share. Since the same lead is also feeding the ECU, there isn't a violent, fuse-blowing short. The aux. air regulator is necessary for starting and proper running, but not for the operation of the injectors, so you can disconnect to test.

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    1983 water cooled vanagon L

    Hi all. I have some questions regarding the pin by pin FI test on the digijet system. For the first time ever, I conducted this test and, as usual when I try new things, it generates more questions than it answers. This is all located on Bentley page 24.20-24.21. Here goes:

    #1) To check the HALL control unit: FAIRCHILD, it says to connect terminal "1 and igntion coil terminal 15". then it says "touch center wire of connecter at ignition distributor to ground". My question is what is terminal 15? Do I interpret this to touch the wire coming from the ignition coil with 1 lead and the other lead to terminal 1 on the multipin connector?

    #2) When checking various components where the specifications state 0 ohms should be the reading, are readings like 2 or 3 ohms OK? I reckon they are. (e.g. the decelerations/idle switch or the full throttle enrichment switch)

    #3) When checking the fuel injectors of the 4 cylinders, the specifications state 16 - 16.4 ohms should be the reading. I was getting 18-19.5 on some of them. is this OK?

    #4) To test the auxilliary air regulator and the relay, right;terminal 86, I am supposed to do "20 and 25 bridged. what does this mean? just create a circuit between pins 20 and 25?

    #5) Finally, how crucial is it to check both temperature sensors at a full range of temperatures. I've read elsewhere at this site about removing the sensor and sticking it in increasingly hot water with a thermometer. when is this necessary?


    Thank you for any answers you offer. Upon my recent readings, attempting to grasp the concepts of fuel injection systems, I have one final question that's not related to the pin by pin tests.
    I've read that the principle variables that the FI brian (EPU) considers when deciding how much fuel to inject is the engine load and the engine speed. My question is what's the difference? Isn't the same amount of air required in each intake stroke to fill the cylinder? would there be a situation when the cylinder requires more or less air intake if it's at the same RPM? what is and how do you measure engine load? OK, thanks, enough questions for now.

    ej

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