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1981 Ford Fiesta poor running when hot

Tiny
ANDEMK1FIESTA
  • MEMBER
  • 1981 FORD FIESTA
  • 4 CYL
  • FWD
  • MANUAL
  • 33,000 MILES
Hi, I have a Mk1 fiesta 1981 1.1L, the problem is: when I start my car and drive away from cold it will pull away lovely with just a touch on the accelerator, the pedal feels nice and light and responsive and the car revs freely and pulls along lovely, then as the car warms up it seems to bog down and needs to be revved harder just to get it to pull, and feels like I only want to use a light acceleration and change up as soon as I can because it seems to be killing it if I try and drag each gear out. I have changed the points, rotor arm, leads, dizzy cap, plugs, condensor, air filter, oil and oil filter, set the dwell angle with a dwell meter, set the timing but it still wont play ball, I am convinced it's once the car is warmed up that is causing the problem.
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Friday, June 11th, 2010 AT 2:55 PM

7 Replies

Tiny
DAVE H
  • MECHANIC
  • 13,383 POSTS
Check you have good fuel pressure from fuel pump when warm
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Wednesday, June 30th, 2010 AT 5:02 AM
Tiny
ANDEMK1FIESTA
  • MEMBER
  • 3 POSTS
Hi, I have a spare fuel pump I could try, is it the fuel pump you mean? Plus, what could make it have low fuel pressure when warm, that would be really handy to know.
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Wednesday, June 30th, 2010 AT 4:02 PM
Tiny
DAVE H
  • MECHANIC
  • 13,383 POSTS
A worn fuel pump will give low pressure and the car will eventually stop running
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Thursday, July 1st, 2010 AT 4:49 PM
Tiny
ANDEMK1FIESTA
  • MEMBER
  • 3 POSTS
I understand that but you said check I have good pressure from the pump when warm, wouldnt the pressure be just as bad when it was cold too?
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Friday, July 2nd, 2010 AT 3:15 AM
Tiny
DAVE H
  • MECHANIC
  • 13,383 POSTS
You should check when cold. Then when hot. The pressure will be slightly lower when hot if the pump is failing internally. You shouold have at least 35psi to keep the car running
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Sunday, July 4th, 2010 AT 6:38 AM
Tiny
NORMAN AINSLIE
  • MEMBER
  • 1 POST
Hi there, hope you pick this up. I have a 1983 mk1 fiesta and I have been having exactly the same symptoms as you for 8 years. Have carried out all the appropriate measures without any improvement. I just wondered if you ever solved your problem?
Regards,
Norm
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Thursday, May 19th, 2022 AT 2:57 AM
Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
Thanks for the addition. It is unlikely that they will respond to this due to it being so old but I think we can solve your issue with a little more investigation.

So let's start where they did. When this is happening we need to monitor the fuel pressure and rule that out.

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

The next thing we need to do is monitor the o2 sensor voltage and find out if this engine is running rich or lean. That will help with determining where to look.

However, if the sensor data shows that the engine is running properly then the o2 sensor is most likely the issue.

https://www.2carpros.com/articles/how-to-test-an-oxygen-sensor-02-sensor

Let's start with this info and then we can take the next step which will depend on what we find with the o2 sensor info.
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Thursday, May 19th, 2022 AT 5:51 PM

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