306 GTI 6 Bogging Down

[DHallworth]

I spent a few hours today trying to help a friend out.

He’s got an incredibly rare 306 Cabriolet. It’s a genuine Dimma. 1 of only 2 ever made. It’s the one that featured in the Max Power magazines back in the day. It was originally yellow but when he got it the paint was trashed so he repainted it. It’s stunning and ever since he’s been here I’ve been looking at 306’s again. My first car was a 306 and it’s reignited that love.

The car is a Phase 1 306 but it’s been transplanted with a Phase 2 306 GTI engine, loom and ECU.

The car is bogging down when trying to accelerate and smells as if it’s over fuelling. It does accelerate but it feels very flat and has very little get up and go to it. Nothing at all compared to what a GTi6 engine should go like.

So far he’s replaced:

Green coolant temperature sensor
Lambda sensors
MAP sensor
Fuel pressure regulator

Today we did a smoke test on the inlet and found no leaks.

Does anyone have any ideas where to go from here? My next thought was fuel pressure but there’s no schrader valve on the fuel rail to plumb in a pressure gauge.

The other thought I’m having is about trying to wire in a diagnostics port straight to the engine ECU.

If we got a diagnostic socket with tails and soldered them to the correct pins on the ECU, would planet talk straight to the engine ECU without going via the rest of the car?

I’m thinking we’d need:

12v feed
Ground
K High
K Lo

If we had a wiring diagram for the engine ECU it might work but am interested in what others think

Thanks,
David.

[xantia_v6]

Don't overlook the possibility of a valve timing error, or a blocked catalytic converter.

[DHallworth]

Good point

One other point to note is that it runs sweet as a nut and idles beautifully. When revving it stationary the engine revs freely as you’d expect. The problems only seen to appear when the car is under load.

[CitroJim]

That's a lovely car David

Yes, that should work for making up a diagnostic socket... Planet should then hopefully talk to it happily...

My thoughts:

Fuel pump getting a bit tired and lazy or partially blocked fuel filter? Can't deliver the required amount of fuel on demand, ECU then tries to compensate by richening up, fuel delivery catches up and then it over-fuels - hence smell of fuel and bogging down...

If fuel pump and filter are OK, check fuel lines for damage resulting in kinking or squashing restricting fuel flow...

Also check the tank vents... A partial vacuum in the tank could cause it too...

And worth checking, if it has one, the carbon canister purge valve and carbon canister itself for leaks/damage causing an air leak...

[MattBLancs]

Odd that the diagnosis port was omitted when engine transplanted, but if can get that wired in then would be my first job. Gives ability for live data and can see what the ECU thinks is going on which should help diagnose. Haynes 306 manual doesn't cover the GTi-6 engine unfortunately so no suitable wiring diagrams from there sorry. There was a Max Power Haynes covering the 306 but I'd guess any wiring diagrams in there don't go beyond how to run a 16 mm² cable from battery to boot mounted amp install

[DHallworth]

We’ve done some more checking and have definitely got it narrowed down to a fuelling issue now.

It’s started choking when under very little load and dipping the clutch is enough to keep it running.

Just need to get a diagnostics port wired up to it so we can interrogate it with Planet and see what’s what.

David.

[DHallworth]

My friend is still having issues with this car. We've not reliably found a wiring diagram for the ECU yet so he's been replacing parts on it.

To date, he's swapped:

Lambda sensor
Air filter
Plugs
Ecu coolant sensor
Fuel filter
Fuel pump
Fuel press Reg
Map sensor
Charcoal and tank breather
Inlet leak test
Cleaned tank and lines
Swapped injectors and rail

He's also removed the exhaust system and checked the catalytic converter.

When sitting stationary the car idles fine and will rev like you'd expect it to. When under load it's got no power at all and takes forever to climb through the revs. The exhaust on it smells petrolly as if it's running rich.

He's got another 306 GTi6 which runs great so he knows what they should drive like.

We still need to try and find the pin outs of the ECU so that we can wire in a diagnostics socket but if anybody has any ideas in the meantime I'd be grateful.

Thanks,
David.

[xantia_v6]

A MAP injection system (assuming that the ECU is correct and fully functional) does not have many ways of running rich. It could be sensing a lower manifold pressure than actual (check the 5V feed to the MAP sensor). I assume that on this engine the MAP sensor is mounted directly on the manifold?

[DHallworth]

Yea, it's right at the front of the manifold, right beside the throttle butterfly.

[MattBLancs]

Coolant temperature sensor (already swapped) is a good shout as to reasons why the ECU is adding more fuel than needed (i.e. because it thinks the engine is cold when it isn't) - shame that didn't sort it.

Is there an inlet air temperature sensor (sometimes part of the MAP sensor I think?) On these engines?

But I'd halt the part swap cross fingers approach until a diagnostic socket is recreated, fault codes possibly, but that live data is what's needed (see if any sensor is reporting a crazy figure. As an example say coolant temperature sensor sensor said it's coolant was at -15°C it's not so ridiculous that it'll raise a fault code, but clearly would be so far from the actual temperature as to affect the running)

It's trying to fix the problem blind at present

[CitroJim]

Throttle pot could be a possibility... It can cause a similar problem on a single-point AX/Saxo...

[DHallworth]

We had another look at the car with Peugeot Planet today after he managed to get the diagnostics port wired in and working.

Initially there were 5 errors on the diagnostics which we believe were caused by sensors being unplugged and plugged back in during diagnostics.

There was 1 permanent fault from the purge canister solenoid valve which we'd expect as it's been removed and bypassed.

There were 4 intermittent faults from:

Inlet Air Thermistor Function - Short circuit to positive or open circuit.
Coolant Thermistor Function - Short circuit to positive or open circuit.
Throttle Potentiometer Function - Short circuit to positive or open circuit.
Inlet Manifold Pressure Sensor Function - Open circuit or short circuit to earth.

We cleared all of the codes and the only one to return was the purge canister code.

Then using the live data we managed to get the below information:

Ignition Values

Injection Values

Sensor Values

I thought the advance looked a bit high but we compared that to his other 306 GTi6 and it was identical. All of the other sensors were pretty much spot on when compared to the other car as well.

When stationary the car idles perfectly and it revs really quickly. It's a bit smokey and smells a bit of unburnt fuel. However, when driving it, it struggles to drive up hills at 30mph even when changing down gears.

The timing has been checked and triple checked and they've used a solid pulley to make sure that the outer of the original one hadn't moved.

Part of me is wondering if it could be a choked exhaust that's causing it so I've suggested removing the lambda sensor to see if allowing it to breathe makes any difference but I'm not holding out much hope.

Any further suggestions would be welcomed!

David.

[CitroJim]

Blocked or partially blocked cat possibly David? Can you do a temporary decat and see if it changes things?

[DHallworth]

Just to close this one out…

The exhaust was removed, the cat was inspected and found to look ok. A spare cat was hollowed out and refitted and it made no difference.

The last thing Graham decided to do was recheck the timing. He’d had someone to do the timing belt on it and upon stripping it down, it was found to be half a tooth out on the inlet cam. Really strange one as it idled perfectly and with no load would rev cleanly and would bounce off the limiter if you kept the boot in it but as soon as t came under load it had nothing.

The car is now back together and driving as it should and passed it’s MOT today too.

David.

[MattBLancs]

Excellent, love a good news story!