More fuel injection problems

[Fraggle]

Hello, Can anyone give some advice? My dad has a 73 TR6, it has a stage 2 head, cam, tuned exhausts and a filter. It has always had hot starting problems, misses then wait for all 6 cylinders to fire, normal for a 6! Anyway we were on our way to a car show yesterday and when we got stuck in traffic the engine starts to miss and black smoke badly then cut out, it seemed to be flooding itself, once on the open road it is ok, i've hada quick look at the metering unit control unit and checked with a vacuum gauge the pipe to the manifold, it pulls a vacuum but drops off very quickly, could this mean we have a hole in the diapham? Does anybody have any ideas?

 

Thank Paul.

[stephen cooper]

Have you had the metering unit recalibrated? Because you will definately need it doing with that spec! That pipe running from the MU - the manifold needs to be tight, check for any splits? Also does the car have braided injector hoses? These may cause problems when hot with fuel vapourisation.

[Andy Moltu]

Sounds very much like a split diaphragm - probably the first thing to check along with the screws that hold the plastic metering unit cover on (They enter the vacuum chamber).

It is also is possible you have some vapourisation - can be worsened by braided injector hoses and worn or perished injector seals or low fuel pressure but the vacuum leak is the likely culprit. Other possibilities include the choke sticking on or too little slack which again makes it run very rich.

 

As for recalibrating the metering unit - a CP metering unit won't be too far off the mark in terms of fuel settings, a CR one may need adjustment. Best done with the use of a rolling road although metering unit suppliers will supply units adjusted for fast road settings. A good way of telling if you need more fuel is to find a nice stretch of road & wind it up to 5000rpm & pull the choke out 1, 2 or 3 clicks (This increases the maximum fuel settings) the exact amount depends on how much slack (in the choke cable) needs to be taken up before it just moves the maximum fuel lever. If you get a surge in power then the max fuel settings may need increasing. If you don't or your power dies off then your existing settings aren't to far off unless you've pulled the choke too far.

 

If your metering unit is recently reconditioned it might be worth calling the supplier to tell them you suspect a split diaphragm first so that you don't invalidate the warranty by disturbing the seals they put over the screws before you do it.