Next up was to try out a different set of injectors. I had a set of M50B20 grey top injectors ready to go in and replace the stock M20b25 ones. The reason I thought I’d try it is that the later type III Bosch design (with four pintle holes spraying fuel out rather than just one) should be better at atomizing fuel, and thereby create a cleaner, more efficient burn. The flow rate for M50B20s is almost exactly the same as the rate for stock 2.5 injectors, so there should be no problems with overfuelling.
While I was under the bonnet I wanted to have a look and see if I could figure why my car was a bit rough from cold start. After plenty of research on the Zone, the C191 plug had been mentioned as a popular culprit. It’s highlighted in the picture below.
The two parts screw apart from each other, so first thing I checked was the condition inside. All good there, but I’d read that mostly the problems are located under the rubber boots before the connectors, so I pulled each of these back and checked the condition of the wiring inside. All looked good but I gave them a quick clean up just for good measure”¦
”¦and that did the trick. Nice and smooth through the revs now, straight from cold.
I moved on with the injector upgrade by removing the fuel pump relay and cranking the engine to release most of the pressure from the fuel system. I then removed the fuel hoses from the front and rear of the fuel rail. The rail itself still contained fuel so I had to have plenty of stuff handy for catching/soaking it up and disposing of it. I removed the brace between the rocker cover and the inlet to get better access for unclipping the electrical connectors from the injectors, then I unplugged the C191 to give me the slack I needed to pull the connector loom box out of the way and expose the four bolts holding on the fuel rail. With the four bolts out of the way, I then removed the six retaining clips that hold the injectors into the fuel rail and then prised the rail off the injectors”¦ although one or two remained in the rail and popped out of the engine. Either way, job done.
The old ”ablue top”a injectors
This shot, although hideously out of focus, shows the part of the injector that counts as far as this experiment goes. The small silver area has four ”apintles”a (holes) instead of one, as used on the older design.
For fitting the new injectors I decided it would be easier to insert the injectors into the fuel rail on the bench and sort out the fiddle retailing clips, and then install the whole thing as one into the engine. To give myself the extra clearance I would need for doing it this way, I removed the rocker cover from the engine.
The new injectors in situ:
And that’s it really. The engine runs perfectly on the new injectors, and there has been no noticeable improvement or deterioration in performance (although they are a little quieter than the old M20 injectors). I’ve not had the car out and about enough to see what kind of difference it has made to economy, which is where I suspect there might be slight gains to be had.
Now that the engine is running well, I think it will be due a remapping session fairly soon, as I have no plans to modify it further for the time being. Apart from maybe a 272/272 cam. I need to give that some thought.
) and all the belts, plugs, dizzy etc were done too:
