A reluctant Starter - Now Sorted by S & C

[revilla]

That does rather explain the issues you have been having.

The ECU will struggle to function on those voltages and even if the ECU keeps going it won't be able to drive the injectors as I suspected earlier.

You either have a problem with the battery, the starter motor or your wiring somewhere. I think that you replaced the starter with no change, so that points to battery or a wiring problem. If it is a wiring problem it won't be so much the ECU connections you need to look at as the wiring in the path of the high current drawn by the starter motor (and really any wiring common between this path and the ECU supply). That would point to the main earth strap from the battery to the block, the earth lead from the block to the chassis or possibly the positive wiring from the battery to the starter (if, and only if, your main loom feeds are taken from the terminal at the back of the starter motor rather than directly from the battery, as is often done if you have an FIA switch). If you do have an FIA switch, all of the wiring from the battery through the FIA switch to the junction terminal on the starter, as well as the switch itself, could be suspect.

I've kind of lost track on this one over time - do you have a multimeter? I think you are going to need to be able to measure the voltage at the battery terminals when cranking. If this drops very low it's a battery fault. If this stays healthy, you will need a multimeter to trace the voltage drop around the circuit.

[revilla]

@Paul, @Jonathan - Looks like we all agree then!

[Jonathan Kay]

SNARK!

Jonathan

[Piers300]

Just to confirm, I fitted a brand new battery 4 weeks ago and also a new starter motor fitted a bit later.  The battery I replaced is still fine, so I can use jump leads and link it up in parallel.

I do not have a cut off Isolator switch. I do have a meter.

So, I need to check all the earth and battery connections -  that I will do tomorrow.

I will disconnect the coil and injectors and check the cranking voltage.

I will also check with my meter the cranking voltage across the battery and from the negative to block and chassis, all as suggested

As far as I am aware the settings in the ECU are factory default and as I had to add the RS 232 connector, I would think no one else had made any changes.

Lots to do tomorrow then.

Thanks for all your input.

 

Piers 

[Paul Deslandes]

snap - 'ish

[Piers300]

Update No 3

As I have a problem with my back (again), Paul Head and Mike Braun kindly came round on Saturday to help. Thank you guys. We first of all reviewed what I had found and re-tested to get similar results.

We initially had 6.0/7.00 volts at the battery at cranking, but a clean up of all the earth's raised it to between 8 and 10 volts but still it would not start. We tested everything we could think of and no joy. We did put a second battery in parallel but nothing except a smell of fuel. So in the end we gave up.

At the end, as we'd had everything apart, we squirted in some fuel and away it went. The only thing that has not been replaced is the TPS and I might try and get one on Monday.

For Paul and Mike, they too found it frustrating and believe it is something quite simple.

 

 

Piers

[Jonathan Kay]

The conventional threshold is around 10.5V while cranking. Did you measure the voltage while cranking with the other battery attached?

Until you're seeing at least that it's hard to diagnose anything else. 

I'd go over all the earths and relevant feeds and battery connections again, including the ECU earth and the fuel pump feed and earth. I'd also measure the voltage at the fuel pump while cranking.

Jonathan

PS: Sorry about your back. What are you trying?

[PaulHead]

Hi Jonathan

We did measure the voltage with a multimeter across Piers new battery and this dropped to about 10.8 whilst cranking which we thought was fine.

The figure that we Improved was the one measured on the Easymap software which went from about 6 to 8.5v after we cleaned all the earths. Basically we think that the Ecu is not getting sufficient volts to fire the injectors (easy map indicates 'no device detected' as soon as you start cranking).  The ecu power supply checked out ok at 12.8 v but On Arnies suggestion we connected the second battery direct to the ecu power feed (purple wire with spade connection to brown / white ECU power leads) but this just replicated previous readings although the smell of fuel did seem stronger at this point - this may have been a coincidence.

i think Piers has now renewed / checked all the various bits except the throttle position indicatorwhich is his next job so not sure where you go from there. One suggestion was Possible problem with the loom? But I'm most definitely not an expert!

Paul

[Jonathan Kay]

Got it

Thanks

Jonathan

[EEK]

After the clean up do you know if you have improved the voltage seen by the ECU and reported in Easimap?

[PaulHead]

Yes, improved by a couple of volts to just over 8 after clean up but still indicated no device detected whilst cranking

[Paul Deslandes]

I appreciate that this is a factory built car, or at least a factory kit, so this may not be possible without serious loom mods, but SBD recommend taking the ECU power leads, +12V and ground, directly to the battery terminals.

Paul

[revilla]

Just a thought, further to Paul's suggestions above ...

I think the voltage drop you are seeing at the ECU is basically caused by the supply current for the ECU and some heavy current associated with cranking going through the same "weak point" of high resistance somewhere. So the voltage drop through that point due to the heavy cranking current is seen by the ECU.

Paul's suggestion basically amounts to sending the ECU supply down a separate route to prevent this.

The other thing you could do would be to send the heavy current that is causing the problem down a separate route. The positive supply side of the actual starter motor goes through its own thick wire straight from the battery, so the problem would have to be on the earth side if it was the actual motor current responsible. You say that you have already cleaned those connections up.

The more likely culprit I suspect will be the smaller but also quite substantial current to energise the starter solenoid. This passes the same fuse and associated wiring as the ECU supply. If there is a point of resistance somewhere along this route, the solenoid current will cause a voltage drop at the ECU.

To test this, you need a length of fairly substantial wire (2mm² or more) with a female spade terminal crimped on one end (if you want I'm quite happy to make one up for you). On the back of the starter solenoid you will find a wire on a spade terminal. Unplug that and attach the test wire. Turn the ignition on an then touch the other end of the test wire to the positive battery terminal (expect a bit of sparking). The engine should crank. I suspect it might actually start. If it does, it's quite easy to add a simple relay to make it effectively work this way permanently.

PS: I really wouldn't go out and buy a new TPS, you've spent enough and I really doubt this has anything to do with the problem you are seeing.

[elie boone]

can it be that the ign barrel has build up too much resistance ? as Paul said connect direct to the battery and this will show up.

[Paul Deslandes]

I've never measured the solenoid current Andrew but I would guess it's a few amps.  The original ground path on my '95 Vx engined car was from the battery neg to chassis and thence to the block.  It's now direct from battery neg to the engine block and then to the chassis for the lights, ancillaries etc., which cuts out one potential (ouch!) voltage drop.

I'm still curious why the engine starts with a supposed malfunctioning ECU after fuel has been squirted in as the ECU would presumably also fail to provide a spark signal.  Unless it fires after the key has been let go and there's enough flywheel momentum.

I'm not going to offer to eat my hat (Paddy Ashdown) or present MOTD in my underpants (Gary Lineker) but I'd be extremely surprised if the TPS has anything to do with it as it runs fine once started and the TPS voltage looks sensible in the data provided.

Paul

[revilla]

@Paul

That pun was worthy of JK  (and I'm not sure if that's a good thing!)

I'm just wondering if the internals of the ECU actually manage to keep going on the reduced voltage (which may be regulated down to say 5V internally anyway) but the injector driver circuits just don't supply enough current to either open the injectors at all, or open them fast enough to deliver enough fuel to fire it.

Only a thought though, maybe barking up the wrong tree. It's a vaguely plausible theory that fits the symptoms but hard to really diagnose without hands on the car.

[Paul Deslandes]

If they're 8 Ohm injectors and all four fire at the same time rather than sequentially, which is all the 967 can manage, the instantaneous injector current at, say, 10V is 5A, so not insubstantial through a poor supply connection.  I think the drivers are power FETs so will just need enough voltage to turn them on.

All speculation of course but gets the old grey matter working.

[elie boone]

It's easy to check if the injectors are working during cranking, take them out of the cil head and crank the engine you will direct see if the injector are working.

 

[Piers300]

Revilla. I just made up a cable to connect from the starter solenoid connection to battery positive and no joy. It cranked fine but did not fire.

The 7 has a key to turn on the ignition and a red starter button to engage the starter motor and as said previously, NO isolator. It is I believe a standard R300K.

i think I now have to suspect the wiring to the injectors and Arnie Webb suggested this at the beginning.

Piers

 

[Piers300]

I have a day at home in the garage, so I fitted a new TPS and as I thought, it made no difference, but I had to do it as the last part of my jigsaw puzzle. I now have a very full spares kit, which may not be a bad thing in the long term, as for me, this car is a keeper.

i have also attached the laptop and discovered that there are three pages to view on Easimap 5.5.

Of course the car would not start from cold, so a squirt of fuel and away it went. On the second page, one of the items Adaptive Status was flashing Red and saying Speed Out of Tolerance. Once it warmed up, the colour changed to orange but was still flashing out of tolerance.

So this is all very new to me. What should I be looking at to give an indication why it will not start from cold?

Piers

 

[revilla]

I still say supply voltage to the ECU and engine loom. If you look back at Post #128 where Aerobod gave you an example of a voltage a reset count trace, are you now in a position to get this for your engine and post it up here?

[Piers300]

Revilla. See post 158. We did that last weekend and feed the ECU from a separate battery.

Piers

[Jonathan Kay]

From post #158:

We did measure the voltage with a multimeter across Piers new battery and this dropped to about 10.8 whilst cranking which we thought was fine.

The figure that we Improved was the one measured on the Easymap software which went from about 6 to 8.5v after we cleaned all the earths. Basically we think that the Ecu is not getting sufficient volts to fire the injectors (easy map indicates 'no device detected' as soon as you start cranking).  The ecu power supply checked out ok at 12.8 v but On Arnies suggestion we connected the second battery direct to the ecu power feed (purple wire with spade connection to brown / white ECU power leads) but this just replicated previous readings although the smell of fuel did seem stronger at this point - this may have been a coincidence.

Jonathan

[Jonathan Kay]

I still say supply voltage to the ECU and engine loom. If you look back at Post #128 where Aerobod gave you an example of a voltage a reset count trace, are you now in a position to get this for your engine and post it up here?

Agreed.

...

Post #158/ #173, I'd try a modified version of that:

• Power the starter solenoid from a separate battery/ vehicle (so that it won't pull the ECU voltage down)
• Look at the voltage at the ECU and the battery while trying to start from that (and see if it starts).

Jonathan

 

[revilla]

I was specifically interested in the reset count rather than the actual voltage reading. Does that increase? Do you still get communication dropouts whilst cranking? If so, it still indicates that the ECU is not coping with the (admittedly slightly improved) low voltage.