What did we screw up??
 

Well, bolstered by the success of my valve adjustment and tune up, I decided to help a friend do the same to his 84 300CD.

We adjusted the valves, changed both fuel filters (pre filled the spin on) and changed the air filter as well.

Car starts right up and idles smoothly, but on the road it is a different story. It accelerates normally and runs good up until about 45 or 50. If you try to accelerate at highway speeds, it will hesitate and stutter (if it was a gasser I would say it was missing) It will not go above 65 or so floored unless you are going downhill, and when it is floored you get a decent amount of black smoke.

Going uphill, it will damn near slow down to a crawl. We started up a 1/2 mile hill at 60, and even floored it stuttered like hell and barely crested the hill at 25! Then going downhill it acted fairly normal until you put it under load at highway speed or hit another hill.

Back home, I re-tightened all the fuel filter connections and the noted the plastic primary filter has only a small fuel bubble in it. Road tested it again, and no change.

As I said, it starts right up, idles fine, and drives well up to about 50 MPH or when you try to put it under load. Then no power at all (no turbo feel either)

Sorry for the long post, but I want to help him fix his rig. Do you think we screwed up the valves? New filters shouldn't cause this should they? A new air filter wouldn't either would it?

I'm thinking a fuel delivery issue But could a bad valve adjustment cause this?

Glenn

I'd hazard a guess and say you bumped off a vac connection somewhere, a boost signal from the turbo to the ALDA on the IP may not be getting where it needs to go, My suggestion is to check them.


also check your linkages, make sure they are not binding up, etc

I have to agree. I'd venture to guess you may have even snapped the banjo bolt line at the back of the valve cover, I've done it a few times myself. They get brittle over the years and become easier to snap than uncooked noodles.

edit: I see you're in Washington, do you make it into Seattle often?

This is not boost or vacuum line related (black smoke?), my guess is some valves were done to the wrong spec.

NO WAY alda is causing a miss symptom. it's gotta be the valves.
you have to measure the gap between the cam surface and the followers. on the passenger's side of the motor.
also, turbo motors need .35mm gap on the exhaust. likely you've got an exhaust or two with intake gap on them.

I caused very similar symptoms while assisting on a valve job. It turned out the be the ALDA line.

In my zeal to "make it better" I cleaned the banjo on the back of the manifold but neglected to tighten it down. The car started quickly and idled smoothly - at low speed. On the drive home the car couldn't get to highway speeds.

The loose ALDA basically caused a great big air leak out the manifold.

I TOTALLY agree, the alda line will dramatically reduce power in the engine but it will not cause the motor to run rough or like a gasser Miss!

Well, I have errands to do today, but as soon as I get the chance I will go over and look at the car. I'll check the ALDA lines and other vacuum lines. If that doesn't pan out we will go over the valves again. By the way, he pulled all three vacuum lines out of the black box on top of the valve cover before I got there and wasn't sure if he put them back in the correct spots. Does anyone have a good picture of where they go? That could be an issue as he said the tranny now shifts WAY smoother than it used to.

Would a mis-adjusted valve allow it to only miss under heavy load but no stutter or miss just cruising along?

yes. this is exactly what a tight exhaust valve would cause.

I will dis-connect the vacuum lines as you said and see what happens. I also would like to swap the fuel lines as mentioned here on the forums to rule out the fuel tank filter screen. What is the best way to do that? Can I swap them where the rubber hoses (from the IP and plastic fuel filter) meet the hard lines in the engine bay, or do they have the to be swapped somewhere else.

To all, Thanks for the help with this so far

If the car ran before the valve adjustment, the problem is something done in the process. Perhaps continue that track until issue is resolved. You don't want to further complicate things.

What did we screw up?? (More info)
 

Ok, found the problem (sort of)

On a whim, I decided to see if the reason the car was running like crap was fuel related and not valve related. It sort of acted like my TDI when I had a bad filter.

Anyway, today I went over to the car and played with the fuel system. I took a spare fuel can and ran a hose from it directly to the IP input(no filter), and then ran the return hose from the spin on fuel filter housing directly back into the fuel can. So in effect, I isolated the car's fuel system, except for the spin on filter.

Took the car out on the road and Holy Crap Batman!!! It ran like a scalded dog. No stutter, no high speed miss, hit 80 MPH like it was not working hard at all. In essence, running fantastic.

Hooked up the regular fuel system lines again, and the car could barley hit 40 MPH floored and stuttered and missed at speeds above 30 or when pressed hard.

SO......Based on what I discovered, There is either a bad primary (plastic) fuel filter, a clogged tank screen, or both. Since I ran the fuel from the can into the IP and the return came from the spin on filter housing I'm assuming the spin on filter was still in the system, and since the car ran great that way, I can assume the spin on filter is OK.

Funny thing is my buddy just changed both fuel filters at the same time we did his valves.

So, what would you do next? I'm telling him we should plan on draining the tank and cleaning the tank screen this weekend and also changing the plastic fuel filter again as well.

Any other ideas?

Thanks,

Glenn

Sounds like you have a handle on it.

Get you some Biobor or Startron and a handful of in-line filters while you are at it. If the tank scren is clogged, you likely have critters in the fuel.

Pull the sending unit out, you might be cleaning it anyway, and take a peek inside the tank. Maybe its just goo around the screen.