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Spi Hesitation On Acceleration - Fuel In Vac Lines / Ecu? Help!


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#1 Jordannn

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Posted 13 June 2018 - 08:47 PM

Hi Everyone,

 

I'm losing my mind over this.....

 

My SPI intermittently hesitates when i accelerate (not specifically when the engine is hot or cold).

 

I've taken it to a garage and they've changed the:

Breather Purge Valve

manifold sensors (lambda / temp .etc)

dizzy cap

rotor arm

crank sensor

 

and its still Hesitating!

 

As part of my own fault finding, I've notices that there is a bit (tiny amounts) of fuel in the vac lines going from inlet manifold to fuel trap, and from the fuel trap to the ecu... I'm going to safety assume the fuel trap should prevent fuel from going into the Fuel Trap --> ecu vac line! Theres also a what appears to be a tiny amount of 'brownish coloured' residue coming from the MAP sensor port on the ECU - my guess is thats petrol!? Am i right in thinking its a good suggestion to take the ECU out and place it over a radiator for a few days to drain any fluids out of the sensor port?

 

Ive blown through and inspected the ends of the 2 vac lines mentioned above - as per Sprockets helpful SPI thread but its still hesitating!

 

Is a good bet to replace these 2 vac lines and fuel trap for new ones - just in case there is any left over petrol residue? (the other vac line to the air filter is all good)

 

any help would be appreciated!

 

Cheers



#2 FlyingScot

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Posted 14 June 2018 - 02:23 AM

Check the output from you throttle sensor. Worn noisy track on this means the voltage increase isn’t smooth but has a “jump” this makes the fuelling do the same. Either back probe the plug when in the car and measure voltage or unplug and use ohms setting and check resistance. Both should be measured as you slowly open the throttle and check the reading increases smoothly.

FS

#3 Jordannn

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Posted 14 June 2018 - 07:43 AM

Thanks for the advice FS! Just a few more questions... if I may?

Am I right in thinking that the ignition needs to be at the ON point (Point 2) and also, should I set the multimeter to 20 Ohms (lowest setting), or the highest setting (being 200k, I think!)?

I know that the connector is wrapped in what I think is heatshrink, so back probing might be harder than just popping a multimeter on the throttle sensor and connector points and checking resistance!

Should the reading stop at a specific number, or is it just the smoothness of the climb that I’d need to look out for?

Thanks!

#4 Jordannn

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Posted 14 June 2018 - 09:10 PM

Check the output from you throttle sensor. Worn noisy track on this means the voltage increase isn’t smooth but has a “jump” this makes the fuelling do the same. Either back probe the plug when in the car and measure voltage or unplug and use ohms setting and check resistance. Both should be measured as you slowly open the throttle and check the reading increases smoothly.

FS


Just checked this and I’m getting 0.91 idle to 3.78v at open throttle!! It was a steady climb and decrease in voltage and I did it again whilst tapping the potentiometer - same result! (The biggest jump was by 0.05v, which I’m assuming as all good:) )

Although whilst my head was under the bonnet I came across this (see pic attached)... do you know if the tube on right should have a clip on it the same as the left? I can move this easily! Maybe this is an air leak of some sort and is causing my hesitation?? (It doesn’t look like a clips been there before though :/)

Cheers!

Attached Files



#5 Bat

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Posted 14 June 2018 - 10:05 PM

Hi,

If there's petrol in the map sensor it's knackered it. You'll need diagnostic gear to read live data from the ECU to see if the MAP sensor is working or not. If so then it's a repair or replacement ecu and a new fuel trap fitted in the correct place.

Cheers  :proud:



#6 Jordannn

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Posted 14 June 2018 - 10:22 PM

Hi,

If there's petrol in the map sensor it's knackered it. You'll need diagnostic gear to read live data from the ECU to see if the MAP sensor is working or not. If so then it's a repair or replacement ecu and a new fuel trap fitted in the correct place.

Cheers  :proud:

Hi,

Thanks! The garage it went to checked the ECU and the MAP sensor wasn't showing any faults - so hopefully its still all good.

 

Its currently in the airing cupboard in an attempt to draw any fuel out of the ECU and fuel trap - so hopefully that will cross a possibility off the list!

 

Cheers!



#7 Jordannn

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Posted 17 June 2018 - 04:42 PM

Hi Guys, just replaced an ignition terminal as the one I had on the car had cracked 3/4 of the way down!

The car seems to been running okay...

Would changing the ignition terminal likely to have rectified the hesitation fault?
My thoughts are that it let through enough voltage to turn the car over, but wasn’t letting enough through when under load (especially uphill) to fire the dizzy, meaning the power isn’t there!

Can anyone confirm my understanding to be correct, or correct me if I’m wrong??

#8 MiniAida

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Posted Yesterday, 10:15 AM

Hi Jordannn

 

The SPi is just as likely to develop "normal" engine problems as any other.

Most people automatically assume any problem is ECU / sensor related (don't worry - I do too), but I would say half of my issues have been standard engine ones e.g. poor connections, leaky head gasket, broken valve etc.

 

Not quite sure what you mean by ignition terminal - do you mean a terminal on the coil? Coils actually draw a fair current, so a crack here would limit this.

Any loose connection on the ignition circuit will cause erratic problems, so if this cures it, then be happy.

 

MA



#9 MiniAida

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Posted Yesterday, 10:21 AM

Oh..... and as I recall, those rubber hoses you showed in the picture - I've got one that is looser than the other.



#10 brivinci

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Posted Yesterday, 02:53 PM

Yes, the hose on the right does not need a clip. 



#11 Jordannn

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Posted Yesterday, 07:59 PM

Thanks for that guys!

Yeah, I do mean the terminal on the coil - it was cracked 3/4 way down, so I made my own adapter! :)

As it was an intermittent fault, I think I’ll have to take it out for a few more runs to make sure it’s actually better!

Cheers!




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