27 replies to this topic

[craig 1010cc]

Finally got my 85 city back on the road with the transplanted running gear from a 98 MPI. All untouched from when we removed it from the donor, other than a service.

I have made life a little more difficult in that I have retained the front subframe, side rad and I'm not running a servo. I'm also running the original centre clock and oil pressure and water temp gauges (I've got a smiths 80mm tacho which I disconnected as it wasn't reading right).

 

1st proper road test (after lots of idling to bleed out the cooling system) and I've got a bit of an issue. It defiantly feels a bit flat (I've had MPI's in the past) and under load there is a misfire, which if you apply full throttle from low RPM, it sounds like it is popping through the throttle body.

 

I've had the plugs out (they've done a couple hours idling and 30 mile drive) and they are like new with just a bit of white on the electrode.

 

Any thoughts? an air leak was the 1st suggestion (particularly where I blanked off the servo pipe), so I shall try squirting brake cleaner about the place to try and pick any up.

[Steve220]

Have you taken over the charcoal canister with it too?

 

Have you double checked all sensors?

[Wiggy]

Are you sure the misfire wasn't there when the engine was in the donor?

[craig 1010cc]

I deleted the carbon canister and have a simple vent pipe on the tank now

We only drove the donor on and off the trailer (it wasn’t roadworthy), so it could be a pre existing fault.

I have change the water temp sensor (the fan came on as soon as we fired it up, the rest are as we got it

[Wiggy]

Although I don't know the consequences of getting rid of the charcoal cannister; I'd do plug gaps, plugs, leads, then coil pack. In that order I reckon.

Coil packs do tend to gradually go, either when hot or when under load. I've replaced quite a few on different cars. Whereas individual coils seem to just die suddenly, in my experience anyway.

[craig 1010cc]

Plugs and leads are new, coil pack could be a good shout. An air leak is coming up as a likely cause, so going to check that first, then try and get the codes read before replacing parts

[craig 1010cc]

Well, some progress.
Tappets, all a bit lose (except 1&2 which were spot on) so reset them to 0.3mm
Fired up, squirting brake cleaner about, no difference so stuck the air filter back on and headed out.
Whilst the water temp was low, no miss and pulled well, as it got above 75 the power started to drop off and an occasional miss returned. So something is breaking down with heat which does sound coil pack related

[craig 1010cc]

Decided to head out after work and put a few more miles on and try a couple of things out. 

1st thing was on start up from cold, if you don't catch it with the throttle, then it fires up and stalls straight away. 1 blip of the throttle and it idles fine.
So headed out (satnav on board to check the speedo accuracy, over reads by 10% so about normal) and sure enough, when it hits 75deg then you start to get a mis. But it wasn't as bad as before. Did get 1 backfire through the throttle coming off a roundabout in 3rd at 20 and flooring it but it didn't feel as bad as before and better than Saturday.
So head to the local tescos to top up the tank with some fresh ultimate as the tank had 5ltrs of fresh super in it and the rest was about 1/2 tank from Sept and the rest who knows (was in the donor vehicle when we bought it). Managed to squeeze 10ltrs in (and the gauge was reading about 3/4's before I topped it, so not far out either). The drive back from tesco's and the mis seems to have gone, but it is still holding back

Decided to whip the plugs out, both the outer 2 are now a little sooty, the inner 2 are both still clean.

[craig 1010cc]

So, more investigations completed. Yesterday I decided to strip out and simplify the breather setup which also meant that the water temp sensor wiring wasn’t being pulled. A run over to my mates lockup so that Rob could plug his diagnostics kit in seemed to run well on the trip over. Still down on power, but no missing. With the diagnostics plugged in, all looked well. Only 2 odd things, the ecu wanted the rad fan on even though it was reading the water temp at 52deg, and the water and oil temp was identical the whole time we had it running.
So headed home and during the last 5 miles or so it felt like he was surging on part throttle (which went away with full throttle) but a couple of times there was a pop back through the throttle body.

[tmsmini]

The oil temp sensor does not interact with the MEMS ECU in a Mini installation.

Try cleaning the contacts for the coolant temp sensor and check the wiring for it. There was a recall a long time ago for the connector, but usually a good cleaning resolves it for a period of time.

[craig 1010cc]

The oil temp sensor does not interact with the MEMS ECU in a Mini installation.
Try cleaning the contacts for the coolant temp sensor and check the wiring for it. There was a recall a long time ago for the connector, but usually a good cleaning resolves it for a period of time.

That makes sense then (but odd to have it and not use it).
The sensor is a new one, but cleaning the contacts on the loom side is a good call

[Steve220]

Try unplugging it and going for a drive. See what it's like.

[craig 1010cc]

So, after re-reading the info above, I realised that there was also a loom change along with the later water temp sensor. As mine had no evidence of being upgraded, and seeing that minispares do them for £15, got one on order. 

 

Went ahead and fitted it, headed out and all was good. Pulled well, didn't seem to splutter or surge so all good. When I got back I decided that the route of the wires wasn't as neat as it could be, so unplugged, re-routed and plugged in.

 

Next day, went back out, and all seemed good. So decided to brim up the tank (as it was just below 1/2 and I don't know how accurate it is at its a new tank) and got on my way. Only to find that the miss and popping through the inlet was back again  so put it away in the garage.

 

Thinking back over what had happened, when I rerouted the sensor wiring, the plastic block on the sensor rotated. Checked with the old one and that didn't rotate (which is the way I'd expect it) so headed out again. Once up to 75deg again the miss came back so pulled over and disconnected the plug. headed out and all seemed good :) only odd thing was that the temp gauge still worked (well went to 90 deg) and the fan was on all the time.

[craig 1010cc]

So, the saga continues. New water temp sensor fitted (genuine rover one) and head out to road test. Once up above 75 deg ( didn’t try at a lower temp) pulls fine until about 3-3500 rpm and then it goes flat. Struggle to get above 45 in 3rd (will slowly get 60 but it’s not happy).

Head back out with the intention of pulling the temp sender wiring to see if that sorts it, but decide after the power struggle coming back I had a random thought about what if its the tank breather causing a vacume/ So I pull over, whip the cap off and head back out. With the fuel cap removed he’s pulling well. Been out twice this evening and with the cap off his run well (happily pulling 45 in 2nd and 70 in 3rd).

 

Go to head over to somerfords, get Pootle out, remove the cap and go to fire him up. Took 3 attempts to get him to catch, but settled to a good idle and off we go. All pulling well, but as we hit 75 deg there is a mis. Decide to push on and he’s still pulling well, but there is def an intermittent miss. 

Return run with the new cap on, pulled well, but after a few mins the miss was back. Seems to mainly be on part throttle but it does seem familiar to when the Si had its crank sensor start to fail so I think I've had 2 issues all along. New crank sensor on order, shall see when it gets here next week if it finally resolves the issues.

[Wiggy]

Good luck!

I'm a little confused though. Is it a missfire or hesitation?

Crank sensors tend to either work or not.

My next thought would be fuel filter or tired Fuel Pressure Regulator, if it's hesitation.