engine shake / misfire

Hey Gang,


I just replaced all the fuel injectors in my TWI Beetle. Before replacement, the engine had very little power, was smoky, and stalled out easy--but, the engine ran very smooth. It felt like the engine just needed more fuel, because a slight push on the pedal and a to-the-medal push accomplished the same amount of acceleration. Anyway, once I replaced the injectors, I had to leave on a month-long trip before I got the engine up and running again, so it sat with all the parts back in their place, but without any action for a month.


Since the replacement, I just got the engine running. The engine sounds much louder, but the whole engine is having a big cyclical shudder (misfire I'm guessing), which it never had before the change. That said, the engine runs smoothly and doesn't die--I left it running in that state about 2 minutes before shutting back off, afraid I might do damage.


You can see the engine shake here (https://www.youtube.com/watch?v=1c3Tbfth0p4). After turning the engine off, a ton of bubbles and gurgling came from the IP, so I'm guessing it was purging air (https://www.youtube.com/watch?v=ng_gxbC9o9g). I cracked the injector nuts and got fuel spraying everywhere, so I know fuel is making it to each injector.


What's my first move to try and get the engine running smooth and even?

More info needed:
Where did you get the replacements?
Did you replace the entire injector or just the nozzles?
What size are they?

I would be tempted to put the old ones back in and then diagnose your limp mode.

I had the original injectors rebuilt at a diesel machine shop. Same size etc. as before.

From what you describe, you redid your injectors trying to fix limp mode or an IP issue.
The injectors may have had nothing to do with the symptoms you had.
If the the engine now runs worse, you may have two problems to address.
At least sort out the limp mode/ IP so you can evaluate whether the injectors are ok.
Have you been changing the fuel filter on a regular basis?

yes, I have been replacing the fuel filter. Additionally, I replaced the tank fuel sender some months ago. The fuel injectors were bench tested at the shop and were out of spec, so I know they needed to be replaced. But I'm sure there could be other problems. What's my first move to solve the limp mode?

Canadian_Grizzly has a great thread about limp mode. All the shaking points to a
fuelling issue and the gurgling is something I've not heard of before but points to
air getting into the system or not being bled out from R&Ring the injectors.

is it possible to have an air problem even if you have lots of fuel spitting out at the injectors? I thought that if you have fuel spray and the engine was running, you were outta the woods.....


Thanks for the tip on Canadian_Grizzly's thread. I'll look for that.

Do you have a clear fuel hose section going into the IP?
That's a good way to see an air leak.

Okay, I just found the thread you're talking about (http://forums.tdiclub.com/showthread.php?t=179589&highlight=Canadian_Grizzly+limp), but I don't think that's it. The car is gutless all the time, including when I'm just starting to drive. I.e., it's super easy to stall the car out, since the power is so low. Before the injector rebuild, I revved the engine to reverse out of my driveway.

Have you checked all the obvious things like: snowscreen, air filter and intake
manifold clogging and ASV function?
It may be time to look for a guru nearby.

I already cleaned the whole intake manifold system out...and it was horrible. The working diameter of the manifold was about the size of a straw. I'll start looking at the vacuum and ASV stuff soon. I had to look up the snowscreen--I'll check that too.


Yes, the lines are clear, and yes, I am getting lots of little bubbles. Being that the engine was running, I thought 1) leaving it running would purge the rest of the air. I've only had it running for maybe 3 mins max. Should I just give it longer?


Also, the shake is happening really evenly, at the same place in the cycle, which makes me doubt it's an air thing causing the shake. Also, if I move the fuel lines to encourage or slow the bubbles shooting to the IP, it *doesn't* affect the shake at all.

If it's safe let it run for a bit. The air should purge. Since we're guessing on what the issue was before, makes it tough to evaluate now. Are the fuel return tubes in good nick? Were the old nozzles bad or badly worn?
The ECU adjusts the fueling for each injector, don't know how long it needs.

In that case maybe one of the injectors is not acting normally.

All of the injectors sort of worked--not quite at the right pressure, or with a terrible dispersion pattern or irregular chatter etc. So badly worn.


Yeah, I'll let it run for a while. I'll post back in a bit.

If you have VCDS look at idle balance. It's entirely possible your "rebuilt" injectors consist of three working ones and one.... not so much. If so that should show which hole is involved immediately, although it won't necessarily tell you WHY that hole is bad (e.g. very low compression will do this as well, although you should get quite a decent amount of smoke if so.)

I just bought a scan tool and hooked it up. (I got the BAFX scanner with the Torque app on my phone.) I'm getting a fistful of codes:
P0103 - Powertrain Mass or volume air flow circuit high input

P0302 - cylinder 2 misfire detected
P0380 - glow plug / heater circuit A

P0402 - Exhaust gas recirculation flow excessive detected


I unsuccessfully cleaned and then just replaced the MAF about a year ago, so I'm hoping that's not it. The injection line of cylinder 2 was really hard to seal--not sure if it got bent a tiny bit at the shop or doing removal. Maybe that's it? I keep getting the glow plug fault, even though I've re-run all the wires into and out of the glow plug plastic 4-tee thing, and it checks out as OK on my ohmmeter. As for the gas recirc issue, when I first got the car, I cleaned out the recirc system--terrible, choking build-up.


My first guess, of the top of my head, is that I maybe I have a vacuum problem. I've read somewhere that vacuum issues can cause engine recirc issues, but also engine *timing* issues as well. Thoughts, anybody?

Interweb guessing P0103 & P0402 wiring/connectors. EGR might be stuck open, could lack vacuum.
P0302 not much for that except fuel or bad compression (not likely). You should be able to see if the lines is O.K. or if it leaks.
Glow plugs, did you check the individual plugs? You can let this go til last.

BobnOH said:

Interweb guessing P0103 & P0402 wiring/connectors. EGR might be stuck open, could lack vacuum.
P0302 not much for that except fuel or bad compression (not likely). You should be able to see if the lines is O.K. or if it leaks.
Glow plugs, did you check the individual plugs? You can let this go til last.

Click to expand...

Yeah, I'll ignore the glow plugs for now. I'll check the vacuum system next, since that seems likely to be implicated in more than one code. As for the injector, no I'm not getting any external leaks, but I've heard that you can have the injector leak internally in the engine (http://forums.tdiclub.com/showpost.php?p=2479427&postcount=4), causing the timing to get screwed up. So after the vacuum system is copacetic, I'll try swapping an injector and see if the fault follows the injector or stays in that same cylinder.

Swapping injector holes is a decent isolation tool (to see if the problem moves) but make sure you have new copper crush washers (or remove and anneal your old ones.) You should also be able to see this in the injector balance display in VCDS -- if that's the cause it should be quite-wildly out-of-spec in that display.

The rebuilt injectors came with shiny new washers. If I take 'em out and swap 'em, do I have to re-anneal them (it's only been 2 months top since getting them new), and if so, how do I do that.

Interweb will help you figure out anneal. Eventually we may be questioning the pedigree on these rebuilt injectors. I suppose I would loosen that one injector nut, see if it squirts. May even give it a light tap with a small hammer.