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1992 Mk5 XR3I Silver Top HELP!


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3 replies to this topic

#1 Mike0911

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  • Vehicle Driven:Escort XR3I 1992
  • Name:Mike Hawley
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Posted 30 July 2019 - 10:24 AM

Hello all. I have been restoring the above car for the last few years and I am within touching distance of an MOT however recently it has developed a running problem that I just can't get my head around.

The engine has been rebuilt and ran well(ish) 6 months ago but a clutch problem meant I couldn't actually drive it anywhere. To get it to run I had to disconnect the TPS once it was fired up (or it would stall) then it would settle down and run and rev freely. I suspected a bad TPS so ordered a replacement. This didn't work at all so I ordered another one, this acted the same way as the original TPS.

So at this point the engine would run fine if the TPS was not connected.

6 months on from this point I was gearing up to swap the clutch but when I fired it up it was much worse than before. It was lumpy, missing and didn't want to be revved. It also wouldn't Idle as it would before.

I suspected bad fuel so I drained the tank and put in fresh, no change.

I suspected the MAF sensor, I fitted one from a newer MK7 (only one available to me!) but it behaved in the same way.

I suspected another electrical issue, an auto electrician could not fault it and pointed to the fuel system.

I suspected a bad fuel pump but I'm getting 42 PSI prime with only 2PSI leakage over 10 mins. I get a +7PSI jump when pulling the suction off the pressure regulator (also no fuel present in vacuum pipe). The pressure remains steady when revving and all the time whilst it's trying to Idle before it cuts out.

I am extremely confused because although the injectors and pressure regulator are new but they have been able to run the engine perfectly well (TPS disconnected) previously.

It feels like a sensor may be going/has gone bad but I'm a bit stumped. Any advice or direction is much appreciated!

Cheers
Mike

#2 PURPLE_2L_LX

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Posted 05 August 2019 - 10:44 PM

42psi sounds a lot for a non turbo engine.

 

I dont have the figures to hand but a Cosworth uses approx 50psi with 30psi of boost.

 

Checked the Exhaust emissions?  Timing spot on?


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#3 Mark M

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Posted 06 August 2019 - 11:07 PM

42psi sounds a lot for a non turbo engine.

 

I dont have the figures to hand but a Cosworth uses approx 50psi with 30psi of boost.

 

Checked the Exhaust emissions?  Timing spot on?

 

I thought 3bar (43.5psi) was the norm for base fuel pressure??? 


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#4 turbopete1

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Posted 12 August 2019 - 04:42 PM

 

42psi sounds a lot for a non turbo engine.

 

I dont have the figures to hand but a Cosworth uses approx 50psi with 30psi of boost.

 

Checked the Exhaust emissions?  Timing spot on?

 

I thought 3bar (43.5psi) was the norm for base fuel pressure??? 

 

 

40-50 seems to be the norm for base pressure for most engines with EFI.

yes a Cosworth will run 50PSI and run 30PSI of boost BUT the pump and regulator keep that pressure there regardless of boost pressure (which is partly why you need bigger injectors and higher flow pumps etc as you wind in the boost for more power).

ive not gone into things too much as regards the effect of boost pressure on fuel injectors/pressure but the only possible issue i see would be at 30PSI boost, which would give you a MAP reading of roughly 45PSI and the cylinder pressure being higher than the fuel pressure, although i believe manu fuel control systems use the base setting as a datum and increase the fuel pressure proportionately to the boost pressure to prevent the engine running lean.






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