Hi all - I was wondering if anyone can shed some light on my situation. My 3 door gets lean when the fans and or any heavy electrical load comes in.
It can be idling at afr 13.8 and when the fans kick in it will lean out to 15.8 - 16 afr and start to hunt! Thats over 2 whole units diff! Is this normal? It will return to 13.8 once fans shut off.



Thanks for any info.

Best.

Tim.

 

Would it be an earthing issue causing an odd signal to the ecu?

I would guess the ecu would normally Richen the mixture to aid cooling

 

Fuel supply issue? Have you tried measuring voltage at the pump when the fans are on?

 

Good call, I expect the loom could be corroded or Earth problem

 

Thanks for replies - the voltage is good underload 13.2Volts fans on. I don't think its a earthing issue either as loom is new. Its a weird one , I wonder if its a voltage compensation issue in the map!


Thanks for input.


Tim.

 

What voltage is at your battery when the engine is running? Is your fuel pump loom and fan loom new?

 

Hi - Battery voltage is 14volt, fuel pump rewired.


Thanks.


Tim.

 

It strange a have a host of stage 3 chips and only on one of them does the AFR remain constant when fans come on.

Odd!

Tim

 

Could you get the car to Stu at MSD (moderator on here) and he would diagnose it and sort it out, I am sure and why not get him to live map it whilst there.

 

I believe this may be caused by voltage drop at the ECU.

Are your fans rewired?

The issue is the fusible links (which supply the overloaded fuse box) build resistance, so coupled with a high electrical demand, results in voltage drop.

Martin

 

What is your solution?

 

As the fans get older they often draw excessive current and may need replacing, always best to check the current drawn by the fans

 

As above also rewire the fans so they are not connected to fuse box.
Replace battery to alternator cable really helps.
BUT also fit an upgraded ground cable from battery to chassis.

Tbh fans only come on while in traffic at idle so it is not too much of an issue imo.

 

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As I say the fans should be rewired, an added advantage of doing this is it alleviates the load on the fuse box.

The fusible links build resistance which results in voltage drop, exasperated with load.

One thing that can happen is the ECU/injectors have a different voltage, which can cause issues. For example, @ WOT the injectors could slow down, leading to a potential meltdown.

Martin

 

Hi all - Thanks for all the input. The fans have been rewired running a separate feed. Also the loom is new and the injectors run an independent feed/relay system eliminating voltage drop at high boost. The fans are relatively new and draw 8amps. Alternator new pos cable and a string of unrated earthing points there is Zero differencial.
Its interesting!
Oh car is not in the UK or I would have been to see stu quite a while ago! Took me forever hunting down a misfire @24psi. Replaced all the usual bits over a period of a couple of years then oil consumption started rising. So took the engine apart and found the inner valve spring on number 4 exhaust broken and a completely missing the stem seal.
valve bounce/oil consumption!! job done.

Thanks all


Tim

 

 

As I say it's the ECU that will be seeing a different voltage, hence it will reference a different part of the map.

People worry about voltage on these cars too much, as long as it's not lean up the top I don't see there is an issue.

Otherwise you would end up rewiring most the car.

Martin

 

The voltage is pretty critical, the age old YB issue we see is at high RPM with lots of boost the Turbo is at its hottest, cooking the Alternator. This is the same time you are demanding optimum fuel delivery, fuel pump voltage, injector speed, coil voltage, so things go bad quite quickly.

I aim to keep the ECU at 14-14.2 under all driving conditions, so coil voltages, injector speed etc remains stable. I commonly see ECU voltage down to under 11v!

If you have 22ms to open and close and injector its critical they remain at optimum voltage for speed, so the injector open time can be optimised, especially on something with fuel limited tunes like T34 803s.

The load site issue isnt really a problem, it just means the map needs a little work, modern fans etc draw less current so the load on the engine is less, so can stop the issue, but the lean load cell still exists, just doesn't get referenced. If the load cells referenced are AFR stable compared to idle you wouldn't even notice the jump in sites.
Cars that are leaner at idle suffer more from moving load cells under slight load than those that are richer.

When we started doing the Alternator to battery cables, we were finding even the Electric windows were operating faster, so its crazy really on the effect it has on the whole car to optimise the battery voltage, after 30 years the wiring is not in good order on most.

 

hi - thanks for input . I think you are right re lean loaded cell. The battery voltage is 14.2volts, the loom is new and one of yours so imagine the voltage at the ecu is ok. (Don't really want to take ecu plug apart as it's lovely.
It is not lean at the topend the problem I have had is the leaning out on fan operation. I have by luck a chip (One of five) that does not have this leaning fan problem, its quite amazing really it idles @ 14.5 afr see 12.3 till 19psi till 6000 rpm then dumps more fuel in till 7000rpm @11.9afr.
Its been tested for det - temps etc - I don,t think you could get much better with a live map!!!


Happy days really.


Tim.

 

But I imagine the supply to be the same?

It wouldn't do any harm, it's simply a case of probing between pin 20 and earth.

You could also measure the voltage @ the injectors by back probing them.

Martin