Talk Morgan Forums Morgan Sports Cars Maintenance & Servicing GDI MOT Update

Trying to visualise and understand how the ECU interacts with two sensors, and thereby making minute changes with the volume and maybe pressure of fuel delivery is mind blowing. The first time I removed a pair of O2 sensors I was shocked that the upstream sensor was clean, but the downstream sensor was black.I expected it to be the opposite.

The tailpipes on my S1 Roadster are always clean, but my GDI was sooty from day 1. Again, logically for me, a clean tailpipe means full combustion and low emissions, but that doesn't seem to be the case.

Using a K&N on my Roadster put the Lambda so weak at the MoT, it was on the edge of a fail, and apparently may also indicate an air leak in the manifold. But the standard filter fixed it.

In terms of the two sensors governing mixture, I imagine that they also talk to the MAF, and throttle position sensor, maybe also revs. How mixture converts into CO and HC emissions should be basic chemistry, but how that looks in the software map is anyones guess.

Absolutely agree on identical cars behaving quite differently. My GDI in bog standard fettle never suffered a hair trigger throttle and pulled consistently from low revs. Pre Club Sport fitment I used inlet valve cleaner both before and after removing the manifold to inspect and clean the valves. In standard trim it never had difficulties at MOT, apart from the 1st time when the engine was presented virtually cold. Now I make sure it arrives for testing stinking hot.

Last MOT - ie with Club Sport fitment - although it sailed through the slow idle test, it recorded 0.178 against a max 0.200 in the fast idle test.

Have just ordered the 02 sensor spacer suggested by Grumpy2 and shall also look at a temporary tailpipe cross section reducer. Just in case...

for those wanting to try a temporary tailpipe restrictor, they are surprisingly cheap

https://www.amazon.co.uk/Exhaust-Muffler-Silencer-Universal-Motorcycle/dp/B08VGQ4DGZ/

It is imperative to present hot, My Audi tested cold at the Audi dealer failed on emissions and they wanted £200 to put it on the computer. I took it away and presented it hot at another MOT station, sailed through. Two MOT's ago the Morgan (Duratec) showed high hydrocarbons but did pass, the last MOT I drove the 10 miles to the MOT flat out in second gear and it showed very low hydrocarbons.

Spot on. but the ECU makes a comparison check between in and out.

My advice was to get one with the narrowest hole possible - 3mm. I read that some users reported no impact using 6mm holed spacers but when the smaller bore was used they worked as described. One chap went as far as machining a 3mm insert into a 6mm bore. Mine were 3mm

Given that the same model can run differently, and that most of the metal is the same, it does suggest that the ECU for each model, was commissioned in batches, and then maybe tweaked on the quiet when issues emerged like rev hang and the GDI fast rev up from cold. MMC sent an ECU upgrade to dealers for the GDI to soften that intiial revving. So unless you check the label on your ECU, against other cars, there is no way of knowing what changed. The hair trigger throttle I had from new made it very hard to set off smoothly, but not all GDIs had that, and it makes no sense.

I'm not aware of any other changes to the engine specs ( I stand to be corrected) but there must have been some updates to the GDI ECU overtime, as the very last models are Euro 6 compliant and produce 154bhp, were earlier cars were only Euro 5 and 145 bhp