hi all. my 307 has developed a really bad misfire at low revs. its was only a slight misfire and intermitent at first but now its bad and all the time. i bought a set of used injectors and fitted them but its made no difference. ive been searching the internet and cant find any answers. anyone got any ideas? cheers, matthew
yes at all throttle openings. there are no engine lights on or faults coming up. before i changed the injectors i took it to peugeot for a diagnostic and they had trouble finding anything wrong because it was intermitant then but they suggested getting the injectors reconditioned. at £130 each i decided to buy the used ones instead at £130 for the set. im thinking of taking the old infectors for testing?
That's probably a good idea, it is possible that you have another duff one, you should be able to make up a good set between them though. Its either got to be the injectors or an ECU problem, on the non common rail engines the pumps could be faulty but that doesn't work on the Hdi as it supplies the same pressure to each injector.
You haven't answered the question regarding smoke. If it is present, is it blue, white/grey, or black? The colour makes a big difference. Is the car ok at higher RPMs? Is diesel clatter very noticeable? An injector fault tends to be relatively insensitive to RPM whereas a fuel pump fault will be sensitive to RPM...
sorry, no smoke as far as i can tell and very little if any diesel clatter. car runs fine at revs over 2k. it doesnt just do it under load neither, it misfires from just reving it up. i thought it could be turbo related as it seems to be fine as soon as the boost comes in but i pulled the intercooler pipe off and it still misfires?
Well, the lack of smoke is interesting, and possibly good news. Smoke at low revs can be caused by low injection pressure, which in a CR system would point to the (expensive) fuel pump. Diesels don't really 'misfire' in the way that petrols do; I would suspect that an injector isn't injecting at all which would give the engine a very lumpy feel, especially at low speed. If you feel confident, you could electrically disconnect each injector in turn and see how this effects the idle/revving characteristics (akin to pulling spark plugs on a petrol engine to isolate the 'bad' cylinder). This will trigger various fault codes and a check engine light, but the latter will disappear when the injector is reconnected.
already tried this but the engine cuts out straight away. after i did this the engine light came on aswell as the 'anti-pollution fault' on the display but both faults cleared when i started it up the next day. my mates got a snap-on diagnostic computer and im going to plug it in this week some time.if there was low pressure in the rail wouldnt that bring the engine light on? what pressure should the rail be at on idle and what other live data readings should i be looking at?
I didn't realises that vintage was so damned smart!
Yes, I would think that low pressure would trigger a fault, there should be a fuel pressure sensor somewhere in there! I know Haynes manuals aren't great, but there should be wiring diagrams in the appendix. They at least tell you what devices should be present for the ECU to operate correctly.
Pressures? I would expect 250-300bar at idle going up to ~1600 bar at max speed/load. Live readings? injection timing would be really good. I can't see why it would be retarded but it would be nice to rule out.
quick update. was advised by someone on another website to remove the fuel pressure sensor and soak it in thinners and that this would cure the misfire but it hasnt. im hoping that this diagnostic will highlight something fingers crossed.
Bad luck. Generally, I find sensors to be more reliable than they are given often given credit for. be careful about 'cleaning' sensors. I know for a fact that many perfectly good MAF and lambda sensors has been ruined by cleaning with the wrong substance.
I feel for you with this problem. It is resisting attempts to pigeonhole very well. I don't think that the RPM sensitivity is entirely coincidental, but it might be misleading. I wonder if there is a corroded electrical connection somewhere-say from the fuel pressure sensor. The fuel pressure sensor sends a voltage ranging from (~1-~5V) covering the full range of fuel pressure from ~300-~1600bar. Fuel pressure, and hence voltage rises with RPM. If the received voltage was unreliable or too low to be plausible at low RPM, it could conceivably b***** up the injection timings. This would also fit with French cars' supposed susceptibility to myriad electrical faults ;)
corroded wire could fit the bill as it was intermitant and not this bad and has got worse over time. id love it if the engine light would come on and tell me whats wrong. ill get it plugged in and see what pops up if nothing then ill start pulling loom apart. i dont want to start buying expensive parts and it not fixing the problem.
No, don't start 'diagnosis by substitution'. If you use parts, whose integrity is not certain, you simply create new unknowns. If you buy genuine new parts, the bill gets big very quickly.
I've made this mistake myself. Threw secondhand parts at a fault-to no avail. Turned out that the connection between the ECU and the wiring loom was sodden. The power supply pin had been completely eaten away. Fix was some awkward soldering and a new wire. Like yours, it was a pig to diagnose, since there was nothing physically wrong with the engine. The new parts are still lying around unused.
I'd be tempted to get the multimeter out and start trying to get some voltage/resistence readings. You might even see some rust! Wiring looms look daunting and tracing them back through a crowded engine bay is a pig. A wiring diagram will give you a good place to start though.
just had a look on ebay at a pressure regulator and ive noticed from the picture that mine is missing the big rubber O ring. could this be whats causing the fault? its not leaking as there is a gasket on the flange?
fixed it! it was a broken wire that goes to the fuel pressure sensor. if you look to the right of the oil filter theres a yellow plug and the wires had broke that come out of the plug. i removed the plug/socket and just joined the 3 wires together. if you have a similar problem just unplug the red plug on the fuel pressure sensor. the car will go into limp mode and the engine light will come on but the misfire will be cured. just repair the wires and the engine light will go out without the need to plug it in.