Pug 306 won't run properly.

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fastandfurryous
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Pug 306 won't run properly.

Post by fastandfurryous »

This has got me a little bit lost:

A 1994 Pug 306 1.6 with TU engine, and multi-point (but all injectors fire at the same time) injection.

While driving, as you accelerate through about 4-5k rpm, the engine cuts out, and the ECU warning lamp comes on. Take your foot off the accelerator, and it comes back to life. If you drive below 4k, then it's not a problem.

Except that the warning lamp will come on, and go off every now and then.

It cuts out regardless of what gear you are in, and will even do it with the vehicle stationary. If you make it cut out, and then keep your foot hard on the accelerator, the engine will almost stall. If you remove your foot from the accelerator as the engine slows, then it picks back up again.

I've had the fault codes read by a very helpful local independent garage, and the only one relevant was "mixture control" which aparently could be anything. Lambda, throttle pot, airflow, etc.etc.etc... and to fix it would be by trial and error.

I'm also having difficulty finding another TU 1.6 petrol injection engine anywhere in breakers yards to be able to swap parts, and to buy them new would be ridiculously expensive.

Any clues? It's only started to be a problem since I had the gearbox off to change a clutch, but every single electrical connection has been checked, and checked again. I've changed the crankshaft sensor (as that was covered in swarf, and could have been damaged in the clutch change) but that has made no difference at all.

Help me!

Thanks.
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pug306
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Post by pug306 »

I would suspect the throttle potentiometer eg a break in the resistive track. Stick a multimeter to the variable voltage output of the throttle potentiometer and check if you get a smooth rise/drop in voltage.

Dont ask me where this is, as I'm a 306td owner.
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Post by pugxpert »

i would be checking your fuel pressure as you drive aand see what it does when you get the fault,mixture regulation fault will come up if your low on fuel pressure also may be check your engine speed sensor
EP6T petrol turbo nice engine in the 207 GT and the new mini....
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fastandfurryous
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Post by fastandfurryous »

Throttle pot: checked, smooth. The engine will actually run (And still has the problem) with the throttle pot disconnected.

Engine speed sensor (on the flywheel): changed this for a known-good s/h one. Same symptoms.

Fuel pressure will be a little interesting to try and measure, but I'll give it a go.

I'm beginning to think that the ECU may be having a tantrum, as just about everything else seems to be working.

Bizzarely, you can disconnect almost every single sensor on the engine (Lambda, Throttle pot, incoming air temperature, Idle control valve, and MAP sensor) and the engine still runs, and still has the fault.

How critical is the air gap on the flywheel sensor?
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pugxpert
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Post by pugxpert »

air gap fairly critical but not adjustable,check also earth lead on gearbox .where it bolts to gearbox and splits one end goes to battery neg the other goes to n/s chassis leg this is the one that breaks at the gearbox end,i think if that is ok check fuel pressure :idea:
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Post by fastandfurryous »

I'll be checking that earth and the fuel pressure tomorrow.

But in the meantime... I can't find an airflow sensor anywhere on the engine. Does it have one? Or does it use the throttle position, MAP and engine speed to determine air mass? And if so, how on earth does it run with the MAP and throttle position sensors disconnected?!?!
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pug306
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Post by pug306 »

If you have access to a scope, check the ECU output signal that drives to the coilpack. If the signal doesn't go flat when it begins to stall, then it could be a temperemental coil pack (at high revs). Let me know if you need the pinout for the coil pack, I can dig it out for you, along with typical resistance values of coils on primary and secondary side.

An even easier test would be to get those neon ignition testers and insert them between HT lead and spark plug. If one pair of plugs starts to die at high revs, then you may have a fault in one half of the double-ended coil pack. Remeber that each pair of spark plug fires twice per cycle simultaneously. Its highly unlikely that both halves of the coil pack will be faulty. Therefore if all four go out, it would point back to a fault in the ECU and/or input sensors.
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Post by pugxpert »

when you unplug sensors they will default to a set value so will still run.no airflow meter not fitted engine load calculated as you said map sensor/throttle position etc...
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Post by fastandfurryous »

Some more things now checked:

Gearbox earth cable, fine.
Fuel pressure doesn't alter when the engine cuts out.
All sparking ceases when the fault occurs.

So. I'm beginning to suspect that the ECU is buggered. It's only started failing since the clutch was changed, which of course meant removing the battery. I wonder if disconnecting the ECU from the battery has killed it... or simply brought on a fault that was already there.

For some reason, the keypad immobiliser hasn't asked for the code in a fair while. I wonder if this is related.

If it does turn out to be the ECU shot, what's the procedure for getting one from another car, ensuring that it's not immobilised permanently? I remember reading something about putting the code in, and then unplugging the keypad, but am not sure of the correct order to do things in, especially when refitting it to another car.
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pug306
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Post by pug306 »

Probablly already tried this, but if you haven't it might help disconnecting the battery, leave to discharge for 15 mins and reconnect. Sometimes a reboot can help!
pug306
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Post by pug306 »

Also, did you check the output of the MAP sensor throughout rev range?
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fastandfurryous
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Post by fastandfurryous »

pug306 wrote: it might help disconnecting the battery, leave to discharge for 15 mins and reconnect. Sometimes a reboot can help!
Well, that's what actually caused the problem in the first place.

But, Ironically, having done this again now, seems to have fixed the problem.....

Poxy electronics. Give me a carburettor any day!

Thanks to all who offered their advice. Just have to see how permanent the fix is now!
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pug306
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Post by pug306 »

ECU's dont take kindly to sparky reconnections. I always try and reconnect the battery terminals short, sharp and firmly to avoid any likely glitches in the ECU.
Lets hope it stays this way!
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