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M35 leaning out after fuel pump rewire

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Equilibrise Community Regular

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Hi all,

I'm a bit lost on this one.

 Installed a Deatchworks DW300 a few years ago and rewired with cable as suggested by Deatchworks. 

Since then the cable has burnt out (melted) twice telling me that there is some resistance there.

To avoid a fire I decided to upgrade the wire size again complete from battery to fuse to relay to the pump including the earth.

Since then the power curve is inconsistent and at anywhere near WOT the engine cuts out and dumps a plume of smoke. When cold the AFR is richer than normal. When hot/engine has been running for a long time there is massive power loss and running extremely lean (AFR16-20) even when gently accelerating from a standstill. 

Any thoughts on weather it just needs a retune, or cable size too big or buggered fuel pump or fuel getting too hot or another biggeted sensor or perhaps something else?

Since its started playing up this time I have replaced the narrowband OEM O2 sensor, MAF sensor and visually checked for intake leaks, however I am certain it is directly related to the fuel pump rewire.

Any input greatly appreciated. 

Equilibrise Community Regular

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Fuel system related mods are:

- Deatchworks DW300

- Siemens 660cc injectors 

- Greddy emanage ultimate 

Its being monitored by a Greddy Infometer touch an Innovate LC-2 wideband

Equilibrise Community Regular

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I'll try to get my hands on a fuel pressure guage and monitor it. 

The confusing part for me is that when cold it runs very rich and when hot it starts to lean out.The symptoms get worse the longer the car runs. I just let it idle for 20 mins then tried to drive, fuel ratio jumped to 20 with very light acceleration then stayed idling at 18 at which point I left the car on the side of the road and walked home. 

The wiring route is exactly the same as previous rewire route which was working perfectly fine apart from melting the fuse and cables at each end. It was still operating,  just getting very hot due to resistance.

Current upgraded wire size is 8AWG.

Duncan Grand Master

Duncan

Posted
Posted

according to engineering toolbox (I'm sure there are other sources too) 8WG over 6m length can carry max 25amp at 12v.https://www.engineeringtoolbox.com/amps-wire-gauge-d_730.html

According to DW, the pump draws up to 18amps so it is close but should not be close enough to cause trouble. https://www.deatschwerks.com/sites/www.deatschwerks.com/files/DATA/DW300 Tech Sheet.pdf

What is the route and distance from the battery to the pump for the +, and what size fuse is in it? And where in that run did the cable melt? And what is the route for - as well?

 

Equilibrise Community Regular

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Thats interesting.

The section of cable between the battery and relay including the fuse holder melted and also a 100mm long section of the negative cable directly off the fuel pump inside the tank melted. It even melted the plug on top of the pump!

The route is about 4.5m long on a 25amp fuse with 30amp relay. The fuse and relay are situated on top of the battery. The cable then runs through the firewall with the engine harness, then on the side of the passenger footwell and under the rear seat to the pump. The new cable completely replaces the old one even inside the plugs and in the pump cradle.

Perhaps I'll try another rewire with 10awg instead.

Can't seem to find anywhere local that sells fuel pressure guage, sensor and adapter so that will take a couple of weeks to get anyway.

Duncan Grand Master

Duncan

Posted
Posted

Wiring sounds exactly right to me. Right size cable, right size relay (larger than needed), right size fuse (smaller than cable max), right order of wiring.

I'd replace the pump next, not the wiring (unless it is damaged again), I think it is drawing way too many amps.  Before you do one possible test is to check the amps being drawn by the pump (you put the multimeter in line with the positive or negative) but check the multimeter can support up to 20amps, I think a lot are limited to 10.  

GTSBoy Grand Master

GTSBoy

Posted
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1 hour ago, Duncan said:

Wiring sounds exactly right to me. Right size cable, right size relay (larger than needed), right size fuse (smaller than cable max), right order of wiring.

I'd replace the pump next, not the wiring (unless it is damaged again), I think it is drawing way too many amps.  Before you do one possible test is to check the amps being drawn by the pump (you put the multimeter in line with the positive or negative) but check the multimeter can support up to 20amps, I think a lot are limited to 10.  

A clamp meter is the smart choice there.

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So, left the car idling and took the following measurements on current draw from the pump:

When running from cold 25 amps.
Gradually drops to 22 amps at operating tempetature with AFR10.
Then after 5mins 21amps with AFR11.
Another 20 mins 18 amps with AFR11.
Another 25 mins 15 amps AFR11.
Another 15mins 14.5amps AFR13.
Another 25mins 13amps AFR14.
Another 15 mins 12.5amps AFR14. When stalled up to 2k at this point AFR18

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Equilibrise Community Regular

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Another 15mins back to 13amps and AFR18-19 when any load put on stall.

External temperature of fuel tank 32deg, external air temperature 16deg. Not sure how to diagnose vapour lock?

RBW49N Community Regular

RBW49N

Posted
Posted
Another 15mins back to 13amps and AFR18-19 when any load put on stall.
External temperature of fuel tank 32deg, external air temperature 16deg. Not sure how to diagnose vapour lock?

Take off the fuel cap
  • 1 month later...
Equilibrise Community Regular

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It's been a while coming, but here's an update:

Got a new Deaschworks DW300 and installed it. On start up it was running very rough (4-5 cylinders) with AFR9. The engine stalled - too rich I suppose. At which point the starter motor packed up (have had signs it would). Solenoid contacts are worn out. After being knobbed around by the autoelectrician who has rebuilt a few of my M35 starters before, it seems the solenoids cant be replaced.

So, installed another 2nd hand starter, got it running and still rough as guts. Discovered 2 spark plugs weren't firing as their tubes were full of oil. 

Over the next few days I'll strip the rocker covers and reseal the worn rubber seals around the spark plug tubes. Hopefully this will sought out the issues its got. 

I'm getting over it. Very close to deciding to part it out.

Thanks for your help fellas

Duncan Grand Master

Duncan

Posted
Posted

I definitely understand your frustration at this point...but the good news is that if changing the fuel pump changed the behaviour, you have found and fixed a problem.

You may be close to fixing it. If the pump was always an issue and the emanage was tuned with a faulty pump, a properly working pump will mean you need a retune. I'd run it up on a dyno with someone who can monitor and correct the AFR and you may be pleasantly surprised (well, it will still be a M35 not a C34, but there's not much to do about that without parting it out....)

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