XJS 3.6 top end power loss

XJS 3.6 top end power loss

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Discussion

AceOfHearts

Original Poster:

5,818 posts

190 months

Friday 27th March 2015
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Having some issues with the Jag over the past couple of weeks with top end power loss and a reduction in fuel economy.

It flags up a FF6 fault under full throttle which is an imbalance between throttle position and AFM reading. I have checked the TPS and replaced the AFM with no improvement. I have also checked the fuel pressure and is fine even under full throttle. The coolant temperature sensor I have also checked and is fine.

This makes me think it is ignition related but not sure why it is still running fine up to about 4000rpm and them it will just basically stop accelerating. It doesn't misfire or run lumpy at all it just has no 'go'

Any ideas?

AceOfHearts

Original Poster:

5,818 posts

190 months

Friday 27th March 2015
quotequote all
Also just checked the throttle and it is opening fully.

Will check the coil next i guess but am getting short on ideas frown

AceOfHearts

Original Poster:

5,818 posts

190 months

Friday 27th March 2015
quotequote all
Coil Testing:

Primary = 2.6 Ohms
Secondary = 7600 Ohms

These seem ok to me but might try and find a substitute coil just to be sure. Ignition amplifier next I guess, not sure how to test this though other than substitution?

AceOfHearts

Original Poster:

5,818 posts

190 months

Saturday 28th March 2015
quotequote all
Thinking of replacing three cheap(ish) bits to try and eliminate them first. Fuel pump, coil and ignition amplifier. Any thoughts?

I don't like replacing bits willy nilly but Im running out of ideas but still need to try and progress

Mr2Mike

20,143 posts

254 months

Sunday 29th March 2015
quotequote all
The symptoms and the fault code match very well, and it doesn't sound like an ignition problem.

As the throttles are apparently opening fully, then a reduction in aiflow must come from upstream of the throttles, so look for a collapsed air hose, blocked air intake or clogged air filter.

The other possibility would be a blocked exhaust/cat.

Edited by Mr2Mike on Sunday 29th March 16:36

AceOfHearts

Original Poster:

5,818 posts

190 months

Sunday 29th March 2015
quotequote all
Thanks, the air filter is new but i will remove it all and try again to make sure it isn't blocked. What is the best way to check the exhaust? Thankfully the car does not have cats but it is still on the original silencers which I guess could have collapsed scratchchin

AceOfHearts

Original Poster:

5,818 posts

190 months

Sunday 29th March 2015
quotequote all
Wow good shout that man! Just had a look and spotted the issue straight away. I'm sure this lump of loose foam was not doing the airflow much good hehe

I had checked the airflow meter and air filter but this air intake tube i had left in the car so didn't spot it. It looks like the foam was surrounding the radiator but has obviously come loose and got sucked in.

I cant get the car out now but am sure this must be it.

Thanks again biggrin



Edited by AceOfHearts on Sunday 29th March 18:09

Mr2Mike

20,143 posts

254 months

Sunday 29th March 2015
quotequote all
No problem, glad you found the cause and it was a cheap fix smile