Iv got a strange intermittent missfire on my 2wd saph that iv had for months and months and im really gettin pissed off with it, i dont get the problem every time I drive it I'd say it happen 8 out of 10 times but some times it don't happen for days and weather conditions don't make any differance, the problem is when I accelerate up to and pass 4k revs the car really pulls back and feels like iv hit a brick wall and gives a nice loud back fire and some times kicks out a flame but anything under 4k and you wouldn't dcdn know there is a problem. Iv tried changing the normaly things but I'm getting no where, has anyone got any ideas on what it could be or what I should look at next?

Iv searched through loads of old posts with similar problems but none of them had posted the cure just the problem.

Things iv changed,
Plugs*
Leads
Dizzy & arm
Phase sensor
Grp a Coil*
Engine coolant temp sensor
044 pump
Fuel pressure reg
Injectors (greens)
Fuel pump rewire

Any help would be great thanks **
** *

 

I reckon its the TPS...

 

How can I check the tsp? I'm sure iv read somewhere you can do it from the ecu pins??

 

I doubt if this is the TPS. That will not cause misfires like this.
Looks like the crankshaft sensor is giving up. Have you checked the gap?
Have you checked the teeth for damage?

Wiring diagram: http://www.bigturbo.co.uk/main6.htm
TPS is on pin 17 of the ecu. (Near) 5.0 volt @ idle, decreasing when you press the throttle.
Also see: http://www.bigturbo.co.uk/main4.htm

 

Iv checked the crankshaft gap and the bottom pulley teeth and they are all fine but iv not yet changed the sensor might give that a go next as my mate should have one laying around.

As for the tps il put a multimeter on it after work as it's a free test and another thing I can rule out, thanks for the links

 

By your list, the only things that you haven't been changed are the TPS, MAP sensor, ignition amp, and air temp sensor. If the crank pulley teeth were damaged, it probably wouldn't run at all, never mind achieve 4000rpm...

But the gap for the CPS might be something to check. Should be 0.6 - 1.0mm between each tooth and the sensor.

A faulty TPS will cut the fuel off when the throttle's open, and create the "brick wall" effect. You'll find it difficult to test it with a meter with the engine running, and while you're driving it.

You really need proper diagnostic equipment like a Pectel monitor to identify intermittent faults like this in real time, or you'll be "chasing ghosts" forever! This will let you (or a passenger!) see in realtime which sensor outputs are wrong.

Also bear in mind that just because you replaced something, it doesn't mean part you replaced was good - you may have replaced a duff part with another duff part inadvertently.

 

Almost defo fuel related, as said do check the TPS you can actually test quite easy with a meter, an assistant may come in handy. Simply measure the voltage at pins 11 and 17. At WOT the voltage should be around 0.6V increasing with less throttle. At no throttle at all on PF01 they it will be open circuit as there is a switch built into TPS.

4x4 PF09 is total opposite of the above and doesn't have a switch.

Check MAP as well.

Martin

 

With the engine off of course, or it'll have the wrong reading and stall.

 

Just spoke to a mate and he's got a good workin tps so I'm gonna grab that off him tonigh and give that a go also while I'm at it il double check the crank sensor gap, is there any way of checkin the cps off the car?

 

Fastest and reliable test would be reading fault codes with a led tester after the mishap.
That probably will give out code 13 if there's something wrong with the Cps or the Phase sensor.

If the TPS would trigger fuel cutoff there would be no bang and no flames.
Back fire and flames are signs of misfiring (no spark) while fuel is still injected. Could also be a problem with the ignition amplifier.

 

This is a retarded question but if I was to put the car into somewhere like grove garage would they be able to easly find the problem or would they do the same as me ie trial and error by changing parts?

I only ask as my whole plan was to sort to car and take it to them to fit a t34 and grays then live map it.

 

It doesn't matter who you use, a fault can only be found if present at the time of looking.
The thing I'd be looking at is the CONNECTOR for the CPS, the loom side the pins lose thier strength and do not grip the pins of the male/engine part, sometimes twisting these slightly so it grips harder on to the male pins in the plug can work only for a few days but proves the point.
The cps should work either side of the gap from just not quite touching to most likely 2mm or more, so not ultra critical.
tabetha