Triumph 2.5 PI troubles

Just after some extra titbits of info here on the basis that I'll give anything a try. I've got a 1970 Mk2 Triumph 2.5PI that's misbehaving with only 15mpg and less than crisp power delivery, black plugs blah blah...

For the history of this subject read the earlier thread on Triumph Acclaims, drill right down to current date.

I understand the system very well now, after checking most of it, and reading all the things available on the net.

Check PRV pressure - reset to 106psi from 120psi. Fuel pump is okay, no hot weather woes, cooling coil fitted. Fuel filter okay, no crud in any of the bits I've had apart. Breathers and return pipes are clear. Engine vacuum is 15Hg at 850rpm, no determinable vacuum leaks. Throttle spindle bushes replaced, butterflies synchronised as near as dammit - small variance in one twinned-pair, one flap opening slightly ahead of other. All excessive mechanical lost motion removed from throttle assembly - idling stable at 850rpm. Recent KMI injectors fitted, two returned as dribbling too much, - replacements have less than conical spray but query how much of a problem this is. Metering unit was recon in 1988, but car has only done a few hundred miles since this. Metering unit springs changed back to standard blue 132bhp saloon, from TR6. Metering unit adjusted to smoothest fastest idle, and all points around this (trying everything).

Engine compression excellent with 170psi per cylinder, valve clearances on the button.

At this point, I'll take any comments on board, on the basis that if I haven't already tried something I'll give *anything* a whirl.

I'd like to keep it as a PI, but a necessary fallback will be to fit 2500s manifold and HS6 carbs - the 2500s had a lower compression and 106bhp, would I be reasonable in assuming more bhp than this with the PI engine and these carbs - maybe just a tad more?

Over to you chaps and chapettes,

Ta, Ken.

This could be a problem. My PI has 5 injectors with a conical spray, and one with what is best described as a bow tie pattern. There is a slight misfire under load a low revs (no sign above 1500) and one plug looks slightly different to the rest. The plug that looks different moves when I move the odd injector.

They wear out quickly if you over rev them. Have you been kind to this unit?

Get everything really warmed up (drive at least 10 miles) and *then* check your adjustments. Mine runs best when it needs just a touch of choke to pick up from idle (500rpm) without hesitation until the temperature gauge is almost up to normal running temperature.

Have you checked that the pipes from metering unit to injector are not getting soft? The pulse of fuel needs to get straight to the injector and not be damped by elasticity in the pipe wall.

Jim

I'm in Solihull, budget? Christ knows - given that I'm holding off from installing 2500s carbs that I've already got then the budget has got to be controlled. Under £150? Also because I've already spent in the region of £250 on the fuel system.

Canley Classics? I'm certainly aware - and have visited - tried to get some bodywork done with no luck.

What's your suggestion? ;-)

I'm strongly believing this now - which leaves me with the prospect of a nice conversation with that nice Mr Witor. Hope he agrees. Twice in the last fortnight the car has literally surprised by running well - sh*t off a shovel. On both occasions I beleive some "blockage" was momentarily blasted away. The injectors are coming out on Sunday for a peak.

Yes, but please define "over-rev" - I never blip the throttle (certainly from cold) like many less-mechanically-sensitive Sunday morning mechanics - and the car rarely gets over 4500 rpm or needs to. The car was idle for ten years - only started periodically by the previous owner. To his credit though, he kept up with sensible servicing and warming up.

I can echo this, and yes I did my adjustments when warmed up.

They're hunky dory - good strong pulses in all - at least when I check, I get the distinct impression that the act of getting back in the car causes one or more injectors to go back to sleep :-(

Thanks Jim - any more comments anyone? I'll report the injector situation next week...

Well there seems to be only two places that get a good press - Canley Classics and Prestige Developments, get your cheque book out for Prestige though! Canley's aren't a body shop although they will do that sort of work. Why not try an email to Canley's - mark it FAO Dave and see what you get. From the little I know of errant PI systems a lot of problems seem to trace down to crappy fuel supply - O rings in metering units can disintegrate and block injectors, filters can fail and the all important fuel pressure can be tricky. Injector spray patterns are critical and often temperamental.

I wonder if you have a blocked breather to the fuel tank? That could give rise to the symptoms you mention. Changing the fuel filter would have equalised the pressure for a while, until the pump creates enough of a vacumm again.

That's a damn fine idea - I'm going out to look now. Would this also cause fuel back pressure at the forecourt?

Wonder how long the vacuum would take to build back up again, I've stuck 40 miles on it since it was "cured".

That's a good idea, is your fuel cap vented? Should it be? I once had terrible trouble after putting a new cap on a mini, being a lazy chap I left the price sticker on it, that covered the little vent hole and the car ran like a dog on the motorway but was fine around town!

While we are talking about venting fuel tanks, I have a Porsche 924S and occasionally when I open the filler cap to refuel I can hear an inrush of air. I don't seem to have any performance problems with the car, and it doesn't happen every time.

Should I be worried?

Mike

My TR7 V8 used to do that all the time, especially after a long drive on a hot day. I never worried, but then again it was a carb system. Fuel circuit breathing can present problems to injected systems - is the 924s Bosch K(E) Jetronic?

I don't think it matters though, as you say there are no performance issues. Or are there any nasty fuel vapour smells whilst driving?

The fuel breather is clear - got under the car, blew air in - watched fuel vapour (distorts the view through air, and stinks) drop out...

I think the 924 uses the K-Jetronic. The 924S uses the same as the 2.5l 944 (Motronic ML3.1?)

No nasty smells and no performance problems. Just a sharp intake of air every time I fill the tank. :)

Mike

Check Air fuel mixture to 4000rpm (colourtune or CO meter)

If this is OK, your distributor might be ropey (shaft profile? bearing wear? not enough advance at higher revs have you looked at the advance/rev change?)

Or

You might have a duff plug which gives up at high revs.

J.

Or One or more plug leads starting to fail. And if you use the wrong length of lead from coil to dizzy or from dizzy to one of the middle plugs, they rub on the inside of the bonnet when it is shut (BTDT).

Jim