i own a 87 fc with a old microtech and when i try and drive the revs get stuck around 4000 rpm even when i put my foot to the floor and hold it, when the car is in neutral it revs fine, only when there is strain put on from driving. i understand this could be an earthing issue if so how do i check that and why would it no hesitate in neutral, any help would be awesome thank you

 

The car has to be under load for the secondaries to kick in which doesn't occur while in neutral. If you simulated load while in neutral, which is done by removing the plug to the TPS and disconnecting and plugging the vacuum hose to the Boost/Pressure sensor then while in neutral the car would likely behave the same way. Try regrounding the engine ground and or the grounds at the ECU. If that doesn't help then you need to see if the secondaries are receiving the proper firing signal from the ECU, or if the electrical injector plugs are connected properly and in good condition or see if the injectors themselves are clogged or not or if the wiring from the ECU to the injectors are fine or if the secondary plugs have voltage on the Black/Yellow wire w/key to on as it should as should the Light Green wire at the same plug when the secondary injector is not firing.

 

Does indeed sound like the secondarys are not coming online when driving under load.

Can you drive the car *gentley* over 4000 rpm? As in slowly go over that four grand on level ground til you get up to say.....4500 or 5000 rpm?

A car NOT under load will be able to get to ??? 4500 rpm using just the primary injectors.

Normally what happens if you have a load on the engine when going over 3800 rpm, is: .....using primary injectors only below 3800 rpm........hit 3800 rpm under load ............primary duty cycle gets cut in half at that point.........secondary injectors come online at that point to make up for the fuel lost by the primary injectors duty cycle being cut in half.......then both primary and secondary duty cycles increase as you keep the pedal to the floor and the car keeps accelerating.

So in your case what happens is.........your under load when you hit 3800 rpms.........the primary injectors duty cycle gets cut in half..............secondary don't come online for unknown reasons......car falls on its *** and won't keep accelerating (remember the primary fuel just got cut in half!).

I doubt the ECU gnds are the problem in your case. Either the secondary injectors plugs (or even just one secondary injector plug) has fallen off or has a pushed back pin in the harness connector.

 

thanks heaps for that, i'll check it out