Peugeot 307 1.4 problems

[alexeft]

Hi all,

I am trying to sort a Peugeot 307 1.4 8 valve.

First of all, it had very high LTFT on gasoline. It was ~32. Surprising it didn't throw any errors. I replaced the MAP sensor. That brought it down to ~20. Much better but not there yet.
Going to have both lambdas replaced, but still wondering if I am right, as, when on gasoline, the pre-cat one fluctuates between 0.1 and 0.8 volts, while the other stays put at 0.8.
Still, it can't be that I have 20 LTFT throughout all revs and loads and not be something generic as the lambda sensors.
What is your opinion?

Secondly, the installer chose to put the injectors up high, but drill the intake from underneath, putting pipes of at least 40cm. I think that it's too long. What do you think on this?

Thanks beforehand for any answers.

[Brian_H]

40cm would generally be considered too long, 30 is normally the limit, though the shorter the better.

My understanding is the post cat sensor should not effect the trims, it's only there to monitor the cat, and should as such throw a error if its detecting the cat isn't doing anything.

Is the 20 fuel trim positive or negative? Does it stay at that when operating on petrol for a while?

[alexeft]

40cm would generally be considered too long, 30 is normally the limit, though the shorter the better.

My understanding is the post cat sensor should not effect the trims, it's only there to monitor the cat, and should as such throw a error if its detecting the cat isn't doing anything.

Is the 20 fuel trim positive or negative? Does it stay at that when operating on petrol for a while?

Thought so about the length of the pipes.

20 fuel trim is positive and stays that way on petrol, along all rpms and loads.

[Brian_H]

That suggests to me you might have a vacuum leak as one possibly, though I've known fuel trims to manage to get stuck, any access to diagnostics that are capable of resetting the trims to default?

[alexeft]

A vacuum leak would be less pronounced at higher loads, but it is not. Ltft is almost flat.

I tried resetting by disconnecting the battery for hours, but nothing happened. It kept its memory intact. I have no tool to do that. Still, fuel trims are not stuck, as proven by replacing the MAP sensor and having ltft go from 32 to 20.

[Gilbertd]

Don't forget that LTFT doesn't necessarily have to be at zero because of the reason for them. The petrol ECU will have it's pre-defined fuelling strategy that assumes that fuel pressure, MAF response, etc is as it was when the car came from the factory. If anything changes from the norm for whatever reason, then the STFT will adjust to compensate and if the STFT is always going one way, the LTFT will adjust so the STFT remains around zero. So the STFT is more important than the LTFT, if that hovers around zero, then the LTFT is doing what it was intended to do.

[alexeft]

For sure things are as you describe, but I am thinking that 20% is too much.

In addition, if the problem was with the fuel pump, i would see ever higher fuel trims at high rpms high load. It would even stumble or pull weakly but it doesn't.

I certainly don't expect the lpg system to work right with a faulty map and lambda.

[alexeft]

On our attempt to replace the pre-cat lambda sensor, the threads are problematic and the old one hadn't been fully screwed.

There's my source of air, driving fuel trims out whack.

More news tomorrow.

[LPGC]

On our attempt to replace the pre-cat lambda sensor, the threads are problematic and the old one hadn't been fully screwed.

There's my source of air, driving fuel trims out whack.

More news tomorrow.

Really that was the source of the problem and there was no noticeable exhaust noise from the poorly sealed lambda sensor?

Some Pugs and Citreons reflect high fuel trims if you keep clearing OBD codes but usually particularly around idle.

[alexeft]

I didn't catch any noise from that area, but then, I didn't look particularly hard.

I will have the car back in a few hours and tell more.

[alexeft]

Finally, got the car back and tested it. What a lovely little car that is. Engine appears more powerful and fuel consumption is only 6.2 liters of lpg per 100km or 45.5 UK mpg. In no case did I expect the last one.
It used to use about 9 to 10 liters. Engine bay was hot as hell. Almost couldn't touch the hood stand after a run in the city. Not so now.
Ltft now at 3%.


To gather up what was done:
- Replaced MAP sensor.
- Replaced spark plugs with Denso's IK series iridium-platinum. The ones with pins on both sides of the gap
- Put the lpg injectors under the intake manifold to shorten the length of the pipes.
- Replaced both lamdba sensors, re-tapping the threads on the exhaust, in order for the sensors to be seated correctly. Made sure their rings were crushed, just like when installing new spark plugs.

Thanks to everyone for their answers.