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82 Rabbit 1.7 violent bucking and jerking

3K views 19 replies 5 participants last post by  DbilasTDI 
#1 ·
I have been lurking these forums for the past 10 years and it has always been an amazing resource and has helped me alot. I have been up and down these forums, posted in facebook groups, and talked to pretty much every volkswagen tech in my area at this point so I finally decided to make an account and post. I bought the car for $800. 90k miles barely any rust and interior is in good shape. 1.7 CIS with a 4 speed manual trans. The first couple of days the car ran great but there was a little popping and sputtering so I did a tune up. Plugs, wires, cap, rotor, fuel filter and air filter. Then the car started misfiring hard under acceleration. Like extremely violent bucking and jerking. I haven't received my voltage regulator for the back of the cluster yet so I had no idea where my temp was at and a friend suggested the radiator could be clogged and that it could be getting hot and creating a vapor lock situation. So I flushed the radiator, replaced the thermostat and replaced the radiator cap that wouldn't hold pressure. Ran the car and used a temp gun to check temps. The car is not running hot at all. Still bucking and jerking. Messing around replacing the vacuum lines I found that with the vacuum advance unplugged the car would run great. No issues whatsoever. So next I timed the car, still bucking and jerking. It seems to only happen after driving for an extended period of time and I read that the car will only read from the 02 when it is warmed up so I unplugged the 02 and drove it. Still bucking and jerking. Last night I went through and replaced all electrical connections and grounds because I'm only reading 12v on the voltmeter on the center console. After doing that I'm still only reading 12v. Honestly I am at a loss here. When not in gear the car will idle and rev smooth as butter. Once you place a load on it it seems to be another story. It seems to mainly do it in second gear and if you keep your foot on it it will jerk like hell but it will power through and then shifting into third it will usually go away for awhile but eventually it gets to the point where it is jerking and misfiring so bad that it wont go anywhere. Anyone have any ideas? I'm sure I forgot some stuff that I have attempted. I have a full donor car for a 1.8t swap but would really like to get this 1.7 running correctly so I can drive the car until winter and then park it and start on the swap. Thanks in advance.
 
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#2 ·
I think it's always funny how people thinking an engine swap will fix all problems. If you cannot fix a basic engine problem, I think swapping the wrong engine in a car is something way over your head.

That said, the car you have is pretty basic. It's as simple as they come but you cannot just start throwing parts at it and expect a miracle. Something I read that someone replaced the bad part, but that is surely by luck.

I like to diagnose. I like to perform tests and let the test results point the problem part. It save you a bunch of money in the long run but it does mean you will be buying tools to perform those tests.

Do you know how CIS works? If not, you need to. Spend a few hours reading how the system works before you open the hood again. Do you have fuel pressure gauges to test the system? If not, do not open the hood until you do. I like this one. https://unwiredtools.com/utcis-cpgauge.asp

Lambda only works when the engine is warm, the O2 sensor is hot enough, AND the engine is not a full throttle. So if you were at full throttle AND the problem occurs, then it's not the O2 sensor. You should have a frequency meter to test the lambda control valve. Yes, another tool you should have.

Once you have a good pressure tester and understand how the system works, you will be able to test the system, get the pressures where they should be, and test the injectors to make certain they are spraying correctly. If all that works, you need to make certain there is no leaks in the intake system. That is difficult to do without a smoke tester. It may be worth spending the money to get that done. Of course, if you have a $1000 or more, you can get a pretty good one.

Then you have the ignition system. Assuming all those parts you replaced are good [new does not mean good], it's possible that the coil is weak. Under load, if the coil cannot produce enough voltage to jump the plug gap, then there will be no spark and that means no fire. A good scope will help you there, but there were few that knew how to use a scope in the past and even less now. Most just plug in the scanner and replace parts that the scanner tells them to. So it may be cheaper to replace the coil vs buying a scope or finding someone with one that knows how to use it.

The car is over 30 years old. Everything in that car is worn out. That is a fact. Do not trust anything in your car unless you have tested it. That includes the factory volt meter. If it's VDO, it may not be reading right. Check the voltage at the gauge and compare the value. If you do not know how to do a voltage drop test, Google it. It is such a simple test that prevents you from cleaning every connection in the circuit that is not effecting anything. Beware, the voltage drop test needs current flowing to test it. An Ohm test cannot have current flowing. Testing the voltage at the battery [while running] and testing it at the alternator should be pretty much the same reading. If it is not, the voltage drop test will help. Remember, do this test at the battery post and clamp. That is the only way to make certain the clamp has the right connection. If you have the cheap aftermarket battery clamps, test the post to the wires too.
 
#3 ·
I literally bought the car to swap it.. and also this is no basic engine problem. I have done plenty of tests. I haven't been "throwing parts at it". I did a basic tune up which is something that needed to be done after the car had sat for years. Then the radiator cap wasn't holding pressure so I figured screw it and I replaced the thermostat just to make sure. Which is a $10 part. I have read up on CIS and cant say I understand 100% how it works but I am learning. I was a technician for 6 years and now work on the pipeline and dont get to be home often. I wanted to get the car running so that I can use it to get back and forth to the shop for the time being and then start pulling it apart this winter. So thanks for your input but there is no need to try and belittle me. Especially with not being familiar with some random mechanical injection system from the 80's that I never knew existed until two weeks ago.

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#5 ·
Not being there, it sure seems like a lot of parts were replaced and you still have the same problem.

My background is that I've been a mechanic since 1980. I started working with Mercedes Benz and after 24 years. While working there, I was promoted to the Shop Foreman in 18 months. After a restructure, I was a Team Leader and my job was to fix the cars that others could not [ie, fix all the comebacks]. I did that for 20 plus years. I was also a top 200 mechanic for 20 years and a top 10 for 2. I own my own shop now. Booked up for 6-8 weeks regularly.

I learned that all mechanics never make mistakes. All learn differently and all diagnose differently. I have learned that I do not replace ANY part unless it fails a test. I have also learned that with testing, you can build a solid foundation to base your decision on. I do understand that replacing maintenance parts is a good idea before diving in deep, but I always understand that I do not want to take all the clients money on maintenance and have none to fix the customer complaint [which was very common at the dealership].

So when you have a misfire under load and then you decided that flushing the radiator would help leaves me puzzled. Yes, the radiator may need to be flushed, but that has nothing to do with the customers complain. I'm certain the electrical connections can be an issue, but with all that time you spent, you have the same issue and without any before/after testing, you have no clue if you did anything better. Again, working with 100's of mechanics in my career, most mechanics will do a repair and then justify it with a ridiculous answer on why it did not fix it.

So, maybe you have some mechanical experience, but focus on what could cause the issue. Make some tests. If you do not have the tools, buy them. It's your money and time to be wasted. You asked for help. Like many other mechanics that asked for my help in the past, I was not always right, but I was rarely wrong. I also understand that most mechanics do not agree how to tackle a problem so you will probably not agree with me at all.

Sorry to sound so salty, but with 20 plus years fixing cars that others could not, the common issue was that mechanics hate to test and only like pattern failures.
 
#6 ·
I understand. To put it simply, I have the money so I am going through and replacing things freely with no concern. I flushed the radiator because we were concerned it was getting hot and creating a vapor lock situation. Also just because I wanted to make sure everything is good. I'm kind of working around the issue and trying to refresh the car a little after it has sat for so long and for everything still being original. I checked the injector spray pattern. It looks good and I had equal amounts of fuel in each can. I did check for vacuum leaks before and found the intake duct was split and I have read the CIS hates unmetered air. I ordered a new one from Ebay and for a temporary fix I went and bought some of that air tight silicone tape and wrapped the tube. Sprayed it down again and its bogging down at the injectors now so I have new viton injector o rings coming tomorrow. I didn't get alot done last night diag wise because I was splitting time between the rabbit and my jetta. I apologize for my ignorance. I wasn't saying I know alot but I have done alot of swaps, builds and repairs and I honestly have never had anything this old. I was a Nissan tech for 6 years and have no experience with anything older than OBD1.

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#7 · (Edited)
And I understand I wasn't really putting as much effort as I should have been. I travel and work a minimum of 60 hours a week and my brain just usually cant function by the time I am home and I don't know if it's just because I have never done it but for some reason mechanical diagnosis compared to electrical is intimidating to me.

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#11 ·
It doesn't anymore. Even with the vacuum advance unplugged it runs terribly now. It will run perfectly fine until you have been driving for awhile and then if you give it any more gas than just a slight push on the accelerator it will buck and jerk. I got my new intake duct yesterday and my new injector o rings and also a gasket kit for the fuel distributor. If it ever stops raining here I'm gonna go out and give it a try today. I've got a few other cars tore apart in the garage so I've been having to work on the rabbit out in the driveway. I leave tuesday for Minnesota and will only be back once a month or so until next year so unless I have some major breakthrough today it's just going to be parked and I'm going to start acquiring the parts needed to put the 1.8t in.

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#19 ·
Have you inspected your fuel fill pipe??
It can corrode on the top side , up inside the rear wheel well. Go on, give it a good ol' reach-around, you will be able to feel if the top surface is corroded out. Or use a mirror and a flashlight. Every puddle and rainy days driven through drizzles amd splashes a little water at a time up-over and down into the fuel tank. Sitting overnight, for example might settle / separate the fuel water blend for the first few minutes But once things get bumpy and curvy on the road again, fuel mixes with the water and intermittently flows through those poor injectors resulting in very poor engine performance and a mild case of whiplash.
I speak from experience. Hope this helps!!
 
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