Not driving smoothly...

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George
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Not driving smoothly...

Post by George » 29th February 2012 - 2:30pm

My fuel injection 72 fastback does not accelerate or drive smoothly at low and mid range revs – it tends to jerk! It does however run fine when the engine is cold- the fault only happens when the engine is warm. I feel this could be a fuel supply issue; when cold, the cold start valve supplies the extra fuel required? Would it be best to start checking the fuel pressure through the system initially or is there anything obvious that would be good to check? The car has been fully serviced (plugs etc) not long ago and I also fitted a new disy cap and leads. Timing is spot on as are valve clearances. Thanks for the help!

paulbu
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Re: Not driving smoothly...

Post by paulbu » 29th February 2012 - 10:50pm


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miketyp3
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Re: Not driving smoothly...

Post by miketyp3 » 1st March 2012 - 10:50am

I'm suprised you haven't had a reply from one of our resident FI experts... :?
There's a engine temp sensor (I think) somewhere (possibly the cylinder head) that triggers an enrichment circuit in the FI "brain"
I think it works using electrical resistance which changes as the tempreture rises.
Perhaps you can check it both cold and hot to see if its working.
Sorry I can't be more help, I've never owned an injected Type 3 so have not yet immersed myself in the workings of one.
I'm sure better qualified help will be along shortly.

Mike
Mike

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alex d
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Re: Not driving smoothly...

Post by alex d » 1st March 2012 - 11:39am

I'm not a FI expert (or in anything else :unibrow: ) but I hear that if your charging voltage is low the FI is going to run rich, so I'd start checking that with a voltmeter first, it doesn't get much easier than that :D

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Editor
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Re: Not driving smoothly...

Post by Editor » 1st March 2012 - 1:55pm

I was busy yesterday, Mike!
Check the cylinder head temperature sensor resistance - it is screwed into the left-hand cyl head, and the wire loins the harness at a single connector usually over the left-hand cylinder tin. You may need to use some needle-nosed pliers to disconnect the connector.

Cold it's around 1,000 to 2,000 Ohms I think. Warm it should go down to about 300 ohms.

If it's open circuit, that would certainly cause an over-rich mixture, which could soot up the plugs and produce poor running at lower rpm.

Alex's advice is good too. You could look at a spark plug and see if it looks black to confirm.

The cold-start system should not do anything unless you (a) are using the starter motor AND (b) the temp is around freezing.
Dave.

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George
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Re: Not driving smoothly...

Post by George » 3rd March 2012 - 11:24am

Thanks for the help- most appreciated. Will give the temp sensor a test and check the plugs.

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George
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Re: Not driving smoothly...

Post by George » 18th March 2012 - 7:23pm

Finally got some free time and took the cylinder head temp. sensor out and measured its cold and hot resistance - seems to be working well and its wires and connectors are all in good condition too. Checked timing again and put on new vacuum hoses on disy. Its just it has no problems accelerating in the high rev limits, and does not seem to be pinking or loosing power- as I would expect from timing problems. Still around 2000rpm it judders and is not smooth to drive. Is there anything else I can check? Thanks!!!

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tris
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Re: Not driving smoothly...

Post by tris » 19th March 2012 - 12:47pm

Do the electric fuel pumps either work or not? Or could it be the case that for some reason it doesnt produce the correct pressure due to mechical wear?

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George
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Re: Not driving smoothly...

Post by George » 19th March 2012 - 2:30pm

Hi- I’ve had a number of standard Bosch fuel pumps on the car, but now it’s running a new Ford Ranger electric fuel pump which produces a sufficient amount of pressure for the car (these pumps are commonly used by type 3 owners in the States as replacement for the standard Bosch pumps) - but with all these pumps, the car has had this problem. Could it be the fuel pressure and might it need adjusting via the pressure regulator?

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Editor
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Re: Not driving smoothly...

Post by Editor » 19th March 2012 - 11:47pm

Certainly could be - 28 to 30psi. Don't go higher though.

There's a stub with a screw in it in the engine compartment to fit a gauge to.
Dave.

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