Low Speed Surging/jerking

dubdoc · Post by **dubdoc** » Thu Aug 13, 2009 6:43 am

I have a completely rebuilt AAZ with a rebuilt/modified pump. Often, at slow speeds and light loads I get surging or Jerking which I can only fix be stepping down hard on the throttle. My old 1.6 TD, and an old AAZ in a Jetta, never had this issue, and it has me baffled. I've even replaced all the motor mounts in hopes of eliminating it, but to no avail. A friend also has a modded AAZ in a Rocco with the same issues. He says it is a result of all the modifications, and is a small price to pay for all the power. I agree, but it sure is annoying.
Does anyone have any ideas or cures for this problem?

82vdub · Post by **82vdub** » Thu Aug 13, 2009 8:53 am

I had a bad injector a while back in my 1.6NA where the engine flat out wouldn't run a specific RPM. The slightest push or pull back on the throttle when you were right at that edge point had a large change in engine RPM. If you tried to hold the throttle in this band there would be a surge, then a drop in RPM's, then surge, etc. It was extremely noticable in 1st gear (it's the highest gear ratio). If you held the throttle at the point where it would surge in 1st gear, it would get progressively worse, unless you moved the throttle to open or close it more to move the engine out of the particular RPM band. It was less noticable in other gears, but there in all gears at that specific engine RPM.

I thought I got a bad rebuilt IP, but after rebuilding my injectors, the problem went away.

Can you see if you can do some more testing to see if there's a certain RPM band (in any gear) that your engine flat out wouldn't run and see if it's a situation like I describe? If I remember correctly, with my problem, in 4th gear (4 speed trans) I could not run the car at 46, 47, or 48 MPH. If I was at 45MPH and gave just a slight amount of gas, it would go up to 49MPH. Same thing when slowing down, it would go from 49 down to 45 and nothing inbetween. Ever gear at the same engine RPM had a range of vehicle speed that the car flat out wouldn't run in.

Post by **Fatmobile** » Thu Aug 13, 2009 12:07 pm

Check all your injection pump mounting bolts.
Even the 2 behind the pump, holding the bracket to the block.

I had a surging in my Golf TD until I did the governor mod.
A 1/16" thick washer in place of the small spring.
Sooo maybe that small spring controls surging and has gotten weak or something.
Just as thought.

Kanzan · Post by **Kanzan** » Thu Aug 13, 2009 9:59 pm

Fatmobile, please tell me more about the governor mod. I have some of the same problems. Thanks, Kanzan

Green79 · Post by **Green79** » Thu Aug 13, 2009 10:41 pm

The other night I was idling along slowly towards a traffic light and the car started surging... but the lights also got bright and dim at the same time. I think it's probably the alternator. Later on, at speed, the lights were fluctuating again, but I was at a high enough rpm that the engine speed wasn't really affected. Seems like a long shot in your case, but might be worth looking into.

Post by **Fatmobile** » Fri Aug 14, 2009 12:08 am

It's hard to explain the governor mod without a picture or a governor spring in front of you. There is a small spring on the end, the spring seats only allow this spring to be compressed about 1/16" before the seats hit.
I remove the small spring and put a 1/16" thick washer between the spring seats.
Green79, I wonder if your stop solenoid is getting wacky.

dubdoc · Post by **dubdoc** » Fri Aug 14, 2009 4:42 am

Thanks, but nada so far. Injectors are new, and all is as it should be. Jerking continues.

82vdub · Post by **82vdub** » Fri Aug 14, 2009 8:29 am

dubdoc wrote:Injectors are new, and all is as it should be.

I replaced my nozzles and replaced the IP with a rebuilt unit. Long story, but by the time I got it running, the IP was way past the warranty period, so returning anything was out of the order. My assumption for my problem was the IP, but it ended up not the IP, but the injectors. So, the problem I described above was a result of new nozzles (ie: new injectors). Just becuase they are new does not mean that one of them isn't bad.

Kanzan · Post by **Kanzan** » Sun Aug 16, 2009 4:44 pm

Fatmobile, Is this the spring you are talking about, for the Gov. Mod.? Thanks, Kanzan

bscutt · Post by **bscutt** » Sun Aug 16, 2009 4:53 pm

here's a thread on governor mod from vwvortex forum

http://forums.vwvortex.com/zerothread?id=3107325

Post by **Fatmobile** » Sun Aug 16, 2009 11:24 pm

Kanzan, No that's not the spring.
The link bscutt posted has a great picture.
I'm talking about the intermediate spring,.. the one in the link has 3 washers where I used one.

dubdoc · Post by **dubdoc** » Mon Aug 17, 2009 8:26 am

Interesting happenings - I am getting desperate...it's getting worse. Last tank I added 6 oz. of Power Service (white bottle) instead of the recommended 3 oz. I also added 2 cups of ATF. Immediately, the surging is almost completely gone.
More to follow.

dubdoc · Post by **dubdoc** » Thu Aug 20, 2009 10:10 am

Problem completely solved. It is fuel related. This time, at Giles' suggestion, I added 3 oz of Stanadyne to my tank of fuel and the problem is gone. Looks like summer fuel equates to "Crap fuel".

82vdub · Post by **82vdub** » Thu Aug 20, 2009 6:39 pm

Didn't think of it until your last post. A couple years ago I started running some fuel additive in the tank of fuel. The car ran like crap, so bad that I ran with the cold start lever pulled out. I got to thinking that it could be cleaning out water that may be in the fuel system, so I replaced the fuel filter and the problem went away.