[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [New Search]
Oh... I just couldnt avoid this invitation.... the FI FAQ!!!! we have the WHOLE WEEKEND to run Amok!! :-) Fuel Injection. It's your friend! By: Keith Park Some pointers and explanation for the D Jet Type 3 FI System. How many of us have a Type 3 where the FI has been ripped out or "Nobody can fix it". Doesn't it seem odd that the simplest production Electronic FI system has stumped the mechanic that just got that new corvette running again?? Why?? Well its because (and I may get in hot water here) most mechanics are just trained chimps.. they can run the equipment and replace the parts that it identified but they just don't understand how the systems work. The D jet systems are really Idiot simple, crude, but very reliable with only a couple things that need to be kept up. I don't pretend to cover all that is in the Bentley manuel so if you don't have it get it as there are many variations on the same basic theme but I will cover the basics and what will happen if they are not there. I will begin with the 1973 E System, I think it's the simplest most evolved system and the most stable. Everything centers around the control unit, NO its NOT a computer but is VERY reliable and you can almost assume it is good as long as no one has connected the battery backwards or something equally as stupid. The Control units must have adequate voltage to them or the systems run rich so make sure your charging systems is up to snuff and using Bosch regulators. This unit then connects to the engine sensors and controls through a wiring harness which can be in rough shape after all these years if people have abused it. Each wire is numbered at each end to make it easy to identify and trace (if the # isn't cut off) and the numbers are identified in Bentley. Some of the rubber boots are avail through WCM and all the little spade connectors are removable from the plastic blocks and avail through various suppliers. If you recondition your harness replace only the ones that are in need, DON'T lose track of the wires (1 at a time) and SOLDER all the connections. IF you are unsure of your skills here have some electronic tech do it for you. Next we'll visit the Pressure sensor, it takes the intake manifold pressure of the intake and through a bellows assembly changes it to an electrical signal to the control unit which can then decide how rich to make the mixture. The engine will not run without it so if an internal coil opens up (not likely) it will cause a no-start and the Bentley shows how to test these. What generally happens is that on the early cars people overfill the air cleaner and the oil works its way into the sensor and gums things up. The bellows can also develop a leak, and these cause the engine to have poor transitional response, run too rich, or hunt a lot at Idle. The 1971 007 sensors are particularly troublesome as the bellows are more fragile and prone to failure. Trouble shooting is to change them out, it's the easiest and they are widely avail used and is a part you should have in your extra parts box. Coils can be tested via Bentley and if they are good it will at least start. Next we'll visit the Throttle position switch, mounted on the right side of the intake air distributor all it does is tell the computer what position the throttle is in and in the later cars how quickly it changes which serves as the accelerator pump on a carbed car does by giving additional fuel if the throttle is depressed quickly. With great care the covers will come off and the contacts can be cleaned with a Q tip and alcohol but BE GENTLE there fragile. If improperly adjusted or loose they can cause idle problems and dirty or broken contacts can cause throttle response to be irradic. These are generally very reliable and not a problem. The 73 cars will idle without them attached at all. Now well visit the most common problem. the trigger contacts in the base of the distributor. All they are is a set of points that deliver a square wave signal to the computer telling it when to fire the injectors. Unfortunately points get dirty by nature and when they go open the engine may cut in and out, run on 2 cylinders only, or not run at all. Points can be cleaned by using a business card soaked in alcohol dragged between the points and released before the edge. NEVER file them as they don't burn with the little current they carry and it will ruin them. With excessive wear, like 150K mi or more, the nylon rider blocks can wear down and cause the points to not open. This can be compensated for by bending the stationary contact in VERY slightly, like .010"; then check with an Ohmmeter how they all work in the distributor with the distributor removed. On occasion the rivets can go bad on the assembly and give a few ohms of resistance so the ohmmeter should read no more than .1-.2 ohms with the contacts fully closed. Reassemble with just a thin smear or Bosch distributor cam lube on the distributor shaft. Do pay special attention to the harness connector, they are critical here too and tend to get abused. Make sure it is inserted in the proper direction as they can get stuffed in backwards on occasion and this will give hesitations on acceleration beyond half throttle. What's next??? Let's do the temperature sensors! The control unit only needs to know 2 temperatures, that of the engine which is done on the 3&4 head and the air temp of the intake air which is done on the intake air dist. When the head sensors go bad the car will track poorly during warmup , run too rich or be hard to start. Sometimes they can go intermittently open and the car will cut out completely at speed then back in again. You can check it with an ohmeter or by subbing in the appropriate resistor to check for intermittent's. See Bentley for the values. The other sensor will cause more of a consistent rich or lean problem if bad, it will be more subtle and be careful as it is easy to get its 2 pin connector confused with the cold start injector connector. Again check with an Ohmeter. The cold start system, on the later cars it is a simple thermo switch that switches in the cold start injector below 32F and a cold start injector that squirts in a little extra fuel. This system is subtle too, I have started mine pretty cold without it connected. The 68-9 cars had an extra relay and a crude electromagnetic valve for the cold start injector. It might be better to disconnect them in warmer climates in these cars as they had the tendency to flood. Next well visit the intake auxilliary air regulator, all this does is to let a little more air around the butterfly valve so the car will have a high idle when warming up. Its controlled by the engine oil temp and is adjustable so if your fast idle is too slow remove the Air reg and you'll see a little slide adjustment, loosen the screw and slide it all the way to the + and tighten it. Other than needing this adjustment they are usually bulletproof. Now this is all there is to the electronic part of the system.. now Ill go into the fuel section, without which the electronics is useless. Keep in mind that any vacuum leaks will drive the system nuts so everything must be tight. THE FUEL DELIVERY SYSTEM Well start with the safety aspect, the fuel pressure is 30PSI so every fuel line should be 10 years old or less, if in question replace them all, its easy and many a Type 3 has gone up in flames from an old leaky fuel hose. With that said, the fuel pump is the heart of the system, very reliable but sometimes get gummed up if sitting for a while. It is operated through a relay under the dash from the control unit. You should get 1.5 seconds of fuel pump pressure whenever the key is turned on, if you don't then trace out why, just take a voltmeter and trace things out. Dirty trigger contacts can cause this too. The pump only takes fuel from the tank and recirculate's it through the system and through a pressure regulator. This also is very reliable but when mine went it let the pressure go too high on startup and the car flooded easily. That's all there is to it! So if the car doesn't run at all make sure you has fuel pressure before proceeding any farther with the control part of the system. Oooops! I did forget 1 important part, the Injectors themselves! All they are is an electromagnetic valve operated by the control unit that with the 30PSI of gas entering them produce a nice fine spray of the appropriate duration. They are pretty reliable but when the cars sit the internal rubber O rings can rust around them and leak. The injector will then leak gas between the plastic and metal sections and is not repairable. The injectors can also suffer from a plugged up screen in the nozzle, some are screens and some are a brass casting but eather way you'll start off with a low RPM miss on the affected cylinder leading to a dead cylinder as it plugs up more. Now your ready to intelligently troubleshoot your D jet FI, keep in mind that I have left out a couple valves and such that are used on the Automatics as I have no experience with them BUT the BENTLEY must be used in conjunction with this article and they are covered in there. Just keep in mind, this is NOT as complicated as it looks and since you have already made the purchase of a Type 3 your intelligence is NOT in question! Relax, and check things as much as possible before replacing them and feel free to ask questions of the listee's (Vwtype3.org). Keith Keith Park Top Notch Restorations topnotch@nycap.rr.com 71 Squareback 65 Notchback 65 Squareback 75 Opel 87 Golf 88 Rx7 10th Anniversary > > Toby Erkson -- air_cooled_nut@pobox.com > '72 VW Squareback, '95 VW Jetta, '81 Gold Wing > http://www.icbm.org/ > Portland, Oregon > > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > List info at http://www.vwtype3.org/list | mailto:gregm@vwtype3.org > >