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Repairing Jammed Or Under Fuelling 300TDi Injector Pump

Repair Guide Repairing Jammed Or Under Fuelling 300TDi Injector Pump

Recently I tried to undo some bad adjustments that were made to my Bosch VE injector pump and despite being very careful to mark everything whilst taking it apart, and putting it all back to stock settings after things didn't go right, I ended up with an engine that would barely run and had no power. I couldn't find much info on this specific problem anywhere and my local independent LR garage were suggesting a replacement injector pump (wrong side of £400!!). Luckily I worked out what was wrong and got good advice, so below is how I sorted it, and some pics to illustrate the process.

I should mention that I had help and advice from Andrew at Alisport http://www.allisport.com - he's a top bloke, I can't recommend them highly enough, without that advice I don't know whether I'd have a working car now or not!

Note - adjustments (i.e. tuning) of the fuel pump are beyond the scope of this article, a quick Google for 300Tdi fuel pump tuning will reveal all.

OK so the problem started when I decided to adjust the diaphragm of my injector pump. Previously the pump had been "tuned" although it turned out that all that had been done was that the smoke screw had been turned in a few turns. This had the effect of increasing fuelling across the rev range, which worked fine on boost but generated way too much smoke under heavy throttle off boost. I decided to wind the smoke screw back a bit and increase the fuelling on boost by rotating the diaphragm. I made sure to mark the position of everything before moving it, and put everything back together. On starting, the engine barely ran at all, and had no power, in fact I could only move her by using low range. There was no smoke whatsoever, not even the usual puff of black smoke on startup.

I remembered that the fuelling pin (the shaft connected to the diaphragm) had been very difficult to get out of the pump, also I had not seen the follower pin in the body of the pump. Putting both of those together combined with the under fuelling I figured that the follower pin was jammed in the pump, causing chronic under fuelling. Andrew confirmed that he's seen this before, so I set about the pump to try and free the follower pin. Incidentally, I later learnt that the reason the fuelling pin didn't want to come out of the housing was that it has a lip on the bottom edge on one side. The correct way to get it out is to rotate it so the tick mark is at the 9 o'clock position, which I believe is the lowest fuelling profile, which doesn't have a lip. Had I turned it back to 9 o'clock when I removed it in the beginning, I probably wouldn't have jammed it to start with.

Anyhow, this is how it looked before i started - my car had (once) an EGR, so it still had the sensor on the throttle linkage:

IMG_5105.jpg IMG_5116.jpg

This is a close up of the throttle arm assembly with the EGR sensor still in place:


You need to unbolt the EGR sensor, then mark the exact position of the throttle arm with respect to the shaft that it connects to. If the shaft is even slightly misaligned, the engine will either not run or be revving. I had been warned about this, so I scribed a mark in the throttle arm (the photo was taken before I marked the throttle arm, but I just scribed in line with the line in the top of the throttle shaft):


After marking the position of the arm, you can remove the nuts and remove the throttle arm. I disconnected both linkages (throttle cable and the other one, not sure what that does) to get them out of the way at this point.

The throttle arm actually has tick marks under the washer, if you removed the washer carefully I guess you could see which one the throttle shaft lined up with, but I didn't want to take any chances so marked it before taking it off. The return spring needs to be disconnected from the throttle arm before you can get it off the pump.

This is a pic of the throttle arm removed from the pump:


OK now you're ready to open the pump and free the stuck follower pin. The pic below shows the pump with the throttle arm off, you need to remove the plug shown with an arrow. It's an allen key fitting, mine came off pretty easy:


With that off, you have access to the back of the mechanism that pushes the follower pin into the governor body. I still don't know what acts on the follower pin to make it follow the profile of the fuelling pin, interested to hear from anyone that knows better. Anyway all I did then was work the pin back and forth using a couple of screwdrivers, you can feel it loosening up after a few goes:


Just to be sure it was going to be in contact with the fuelling pin, I put the diaphragm back in, and pushed the follower pin into the pump from the back.

From that point on it's a case of refitting is the reverse of removal, making sure you line up the throttle arm with the mark made earlier. I found that despite marking the throttle arm I still had to mess about with the idle to get her running properly, but it was much easier having a starting point. One final tip, make sure when you put the throttle arm back on (which is a PITA because you have to get the return spring on properly first) that you don't end up wedging one of the linkages behind the arm. I ended up taking the throttle arm off at least 4 or 5 times because of one thing or another.

Happily after all this messing about, once I got everything connected back up, and after a bit of fine tuning, she's running sweetly again. Still might be smoking a wee bit more than I'd like but I know what I'm doing now so am happy making finer adjustments. I hope this info is of use to someone, had I seen pics like this beforehand it would have been very useful to me. I nearly booked her in for the £400 pump replacement which would have been money down the pan.


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