Scottish Elises

Crossposted from SELOC...

Hey folks, any advice as to the following would be much appreciated...

Out on a run on sunday and the engine started hesitating at low revs/hard acceleration. Pushed on and at high revs it felt fine, but about an hour later, the car stopped feeling 'right' and I was struggling to accelerate past 70mph. Pulled over and the engine coughed a few times as the revs dropped then died. I let the temperature come down to mid 80's (from 94deg) then tried to restart. Plenty of turning over but no ignition. Basically, tried a few things at the roadside, the AA tried a few more when they finally showed up and the upshot was I went home on the back of a trailer.

Plenty of fuel (26litres), plenty of water and oil (and no mayonnaise or fluids where there shouldn't be!). Fuel pump is priming (and the fuse is fine), there's fuel down stream of the fuel filter and at the return end of the fuel rail. The engine cranks over fine so starter is good and I've pulled off all the multiplugs and refitted. There's good spark at the dizzy and although there is some corrosion at the rotor contacts, there's a good spark at the first plug (only checked one)

The usual suspects;

1) Immobiliser failed? - don't think so as both circuits seems good - engine cranking and fuel pumping

2) MFRU? - don't know. Can this cut power to the ECU?

3) Crankshaft or Camshaft Sensor? - maybe. If the spark is just firing randomly then could this explain it?

4) Distributor Cap and Rotor arm? - seems unlikely as there's a spark at the plug but I've ordered a new pair anyway as they needed changed out

5) Coil? - AA guy reckoned that he'd seen coils that would give a spark when the plugs were out but not once they were back in the head and under pressure...

6) Jammed closed throttle body? Although it should surely idle, no?

7) Stepper motor, manifold pressure sensor, IACV or throttle potentiometer - no idea but understand that they can all cause poor running/failure to start

If anyone can shorten the list, then it'll save me time and money. Or I guess, can anyone suggest something else I haven't considered?

Cheers
Matt

UPDATED;

I've fitted the new dizzy and as expected no change. Guys on SELOC seem to reckon crankshaft sensor, so I've got one ordered...

Any other ideas? Only other thing I can think of is that the Esso on Holburn Street is selling water as Super Unleaded...

Audi time.

HT leads?

Are the spark plugs okay?

Might be worth checking all plugs spark.

Don't know enough about crankshaft sensors and ECU's to be of any further help though.

offshorematt wrote:Crossposted from SELOC...

Hey folks, any advice as to the following would be much appreciated...

Out on a run on sunday and the engine started hesitating at low revs/hard acceleration. Pushed on and at high revs it felt fine, but about an hour later, the car stopped feeling 'right' and I was struggling to accelerate past 70mph. Pulled over and the engine coughed a few times as the revs dropped then died. I let the temperature come down to mid 80's (from 94deg) then tried to restart. Plenty of turning over but no ignition. Basically, tried a few things at the roadside, the AA tried a few more when they finally showed up and the upshot was I went home on the back of a trailer.

Plenty of fuel (26litres), plenty of water and oil (and no mayonnaise or fluids where there shouldn't be!). Fuel pump is priming (and the fuse is fine), there's fuel down stream of the fuel filter and at the return end of the fuel rail. The engine cranks over fine so starter is good and I've pulled off all the multiplugs and refitted. There's good spark at the dizzy and although there is some corrosion at the rotor contacts, there's a good spark at the first plug (only checked one)

The usual suspects;

1) Immobiliser failed? - don't think so as both circuits seems good - engine cranking and fuel pumping

Yep, cannot be immob, else it wouldn't run fuel pump or spark.

2) MFRU? - don't know. Can this cut power to the ECU?

The MFRU supplies the main current to the ECU and all of the inductive loads (coils, injectors, relays, stepper motors, etc.). If you are seeing sparks at the plugs then the Main Relay is engaged.

3) Crankshaft or Camshaft Sensor? - maybe. If the spark is just firing randomly then could this explain it?

Assuming car in picture is your car, you don't have a camshaft sensor (unless it's a VVC; even so the absence of the camshaft position sensor wouldn't make it not start I believe, though it would probably refuse to run above 5,500rpm).

You do have a crank position sensor, but the ECU wouldn't fire the sparks without it working, so won't be that.

4) Distributor Cap and Rotor arm? - seems unlikely as there's a spark at the plug but I've ordered a new pair anyway as they needed changed out

Unlikely if you're seeing any spark at the plug, which you say you've checked.

5) Coil? - AA guy reckoned that he'd seen coils that would give a spark when the plugs were out but not once they were back in the head and under pressure...

It's possible but not something I have heard about on an elise before.

6) Jammed closed throttle body? Although it should surely idle, no?

For starting throttle is always closed (unless you're a bad boy and press the gas pedal while cranking, which you should not). So like you say, it should idle with the throttle closed.

7) Stepper motor, manifold pressure sensor, IACV or throttle potentiometer - no idea but understand that they can all cause poor running/failure to start

Failed IACV could cause the non start, but would be worked around by either opening throttle with gas pedal or by removing IACV completely - be ready to kill ignition in latter case - don't know how fast it will rev in this case.

MAP sensor is not required for starting and in your car (assuming it's non VVC) is built into the ECU (the white and black rubber hose from the manifold to the ECU carries the vacuum to the ECU).

Coolant temperature sender could have failed, but in this case I would expect you to be able to start it on the throttle, even though it won't idle.

The cat could have collapsed, but I would expect that to have given symptoms at high revs first, and it should still start and idle just not rev hard.

As an experiment, try starting it with the throttle flat on the floor and let us know.

My personal favourite is a dodgy common +12v on the fuel injectors, meaning that although you have fuel running round the loop, the injectors aren't opening to fill the intakes. There's quite a large connector just underneath the throttle body which takes all the injector wiring - it would be worth splitting that and looking for corroded connections.

Another option is a vacuum leak into the manifold causing it to run too lean to idle, but I don't think this is likely (more likely it would just idle faster).

Cheers,
Robin

Robin

I had a couple of attempts with it, no throttle or full throttle was no difference.

It was actually firing and spluttering for a couple of seconds, but then cut out.

Healthy spark from output of distributor, so I suppose suspect is fuel not getting to spark.

tut

Could it be a fuel pressure problem? Fuel is getting thru the filter but is it at high enough pressure for the injectors to work? Blocked fuel filter? Tired pump?

How about something daft like the fuel pressure regulator has gone tits up and is letting all the fuel return?

How odd...

Matt

Dirty fuel filter and air filter would be indicated by a gradual loss of power, not a non start as in your case, so going back to basics we are looking for a continuous spark at the plug, and supply of fuel into the chamber.

tut

Have you changed the spark plugs? It could be that they are failing underload or even the HT leads as Mack suggested.

What's the condition of the plugs like - could it be that the air filter is blocked and leading to overfueling? (leaves, passing small child?)

You mentioned 94c - is that the temp whilst driving or parked up at the side of the road? Can we rule out HGF that's going into the cylinders?


Really on a step by step basis - get hold of either a new or know set of spark plugs and leads - give them a try on an individual basis (change plugs - if nothing change leads) from there swap over the ecu nd just take it bit by swapping over (even temporarily) for know good items.



HTH


Mac

Really on a step by step basis - get hold of either a new or know set of spark plugs and leads - give them a try on an individual basis (change plugs - if nothing change leads) from there swap over the ecu nd just take it bit by swapping over (even temporarily) for know good items.

Why pick on those items, especially when it seems clear that there is a spark?

I would start at the fuel end instead!!

Cheers,
Robin

I'm guessing here that the engine's plug weren't removed and tested but a spare one used for checking for a spark.

Also by removing the spark plug you would be able to check the plug end for fouling. I'm just trying to think about reasons for the car losing power before it died.

And besides - it's way easier/cleaner to start there

Mac

mac wrote:I'm guessing here that the engine's plug weren't removed and tested but a spare one used for checking for a spark.

Also by removing the spark plug you would be able to check the plug end for fouling. I'm just trying to think about reasons for the car losing power before it died.

And besides - it's way easier/cleaner to start there

Mac

We removed the the engine plug (left hand side of engine) and turned car over. There was spark.

I agree with Robin that it could be a fuelling problem.
As Matt said, no sign of any HGF

Assuming it's the non-vvc model, the wire you're looking for is brown and pink (quiet, shug et al). The connector is smaller than I thought - it's a 3-pin connector that hangs off a bracket that is bolted to the throttle body. The brown and pink wire is the common and should have a solid +12v when the ignition is switched on. If this connector is corroded then you will get poor injector opening; also as the engine is running the connector will heat up and further increase resistance, leading to total failure to open injectors. Higher revs would be worse (higher average current through this wire).

It fits the facts, so go check it

Not much use to you perhaps but I have a complete spare engine with all the sensors on it here in Edinburgh ...

Cheers,
Robin

robin wrote:The cat could have collapsed, but I would expect that to have given symptoms at high revs first, and it should still start and idle just not rev hard.

I had the cat on my old 106GTi collapse and it was a sudden loss of power followed by the car stalling and refusing to idle. It would start but die again instantly.

could be cat collapse

could be the main feed to the dizzy failing under load - I had this once. It worked fine with no load, looked ok, but load made it fail.