Puzzling Starting Problem - OMEX 600 - solved!

[Davemg]

Thought I'd share a recent experience. Apart from the Quantum we have a Rover Mini, with OMEX 600 and throttle bodies on an A series. Cold starting was a nightmare, and far worse following an engine out refurb.

After much investigation and a visit to the superb guys at ATSpeed in Basildon, a few lessons....

a. Eventually realised the battery was knackered, down to 9.9v terminal voltage on cranking. The volt drop negative terminal to engine block was just 0.12v and positive side to ignition coil was 0.6v; so not my wiring! Eventually bought the biggest flippin' battery I could get, and went from 45Ah 330CCA to 80Ah 760CCA! Oddly it had just enough poke to start the engine when warm (after using a jump starter when cold).

I should add the lack of starting was due to a lack of sparks. When the battery voltage dropped, the output of the ignition coil also dropped to a point where there was insufficient voltage to jump the spark plug gap.

b. On ATSpeeds' advice, ran a separate ground wire from the ECU back to the battery. It's not obvious but the negative power to the injectors and ignition coil all run via the OMEX ground lead. It's essential this is a clean ground.

c. Most surprising of all, the Crank Position Sensor lead, which is screened, is highly susceptible to noise. I had run a number of cables, including main power, in some 20mm spiral conduit. The OMEX was getting inconsistent pulses (Stat Sync). I took the cable out, put it in its own spiral wrap, and ran it about 15mm away from the rest of the cables. Pulses now absolutely perfect.

It did give me a good excuse to buy a clamp meter with a DC current measurement so I could check our cranking current - 159A - and a battery tester from MachineMart (always an upside...) but more importantly, she started.

MOT this morning and it's a tad fresh so hopefully ok for starting.... fingers crossed!

Hope some info there helps someone.

[greenwoo]

Most surprising of all, the Crank Position Sensor lead, which is screened, is highly susceptible to noise.

Interesting as a muppet i'd never have thought/known of that....

[Wingco]

Thats very interesting Dave, I am know machinic/ sparky but that acctually made sence so well put that man.

[DJ.]

Interesting

I hope you got the MOT ok, I went for mine this morning, it was freezing, and the I had hail as I went up the hill towards Snodhurst garage

At least ear defenders stop the hail hitting my ears

Duncan

[Rob E]

At least ear defenders stop the hail hitting my ears

Duncan

Can you imagine me in a hail storm then ....... leave it
Good write up

[davehall]

Really interesting. I’ve got a cold start problem with my Zetec so this is something to investigate.

[Davemg]

Thanks all, yes this one had me puzzling alright. Not just one cause, but a few.

MOT passed (yippee!) but now back home, lots more to do to bring the car up to standard.

The CPS noise thing is very odd. I've now got all the electrical wiring to the engine: starter/alternator/ignition coil/Lamda/injectors/temperature sensors in two spiral conduits plus a spiral wrapped screened cable for the CPS, just very loosely cable tied together with some nice wide ties.

[jeffw]

I once had the situation where the car would stop every 20mins, wait 2 mins and it would restart. This went on for several weeks until I took it to Omex and they left if running in their unit with a laptop attached. At the 20min mark it would lose crank position and stop, turned out there was a break in the CPS lead which opened up with heat and caused the issue. New lead and not further problems.

[Nash]

At least ear defenders stop the hail hitting my ears

Duncan

Can you imagine me in a hail storm then ....... leave it
Good write up

Hahahaha
That's funny