350i running problems yet again
Discussion
Hi everyone,
I'm still having some random running problems with my flapper 350i. Previously, I thought I had cured a misfiring type issue by resoldering the ecu, but the problem seems to have returned again.
In brief, when cold, the car seems to run reasonably well. I say reasonably as its not really been used much over the last few years and can go 4 or 5 months between leaving the garage.
Anyway, I drove 15 miles or so in it the other day and it seemed to be running perfectly. I filled up with fuel, and straight away it starting feeling like it was misfiring again. I headed for home, but managed to narrow the fault down to a certain set of paremeters.
So, when accelerating, the car runs nicely and pulls as strong as it ever has. If you coast, again its smooth. You can accelerate through all the gears - no problems at all. However, if you try to maintain a set speed with a little bit of throttle, the engine seems to misfire, the car jolts, it sounds rough through the exhaust etc. Apply a little throttle and it all smooths out instantly, reduce throttle to maintain speed again and it misfires.
I put the car into third and went from 2000 rpm up to 3000rpm and it pulled smoothly, however at say, 2200rpm, if you try to maintain a speed with whatever degree of throttle is needed, the engine struggles. Drop a gear and give it a bootful of throttle and it rockets, maintain speed and it misfires/judders.
Anyone ever had this? I'm feeling like its going to be something simple like the vac advance on the distributor, or maybe its still a knackered ecu. Perhaps the timing is now out due to the distributor, or maybe its a fueling issue. I've done all the usual Lucas electical tests in the diagnostics document and everything seems fine.
Any ideas?
Thanks,
Dan.
I'm still having some random running problems with my flapper 350i. Previously, I thought I had cured a misfiring type issue by resoldering the ecu, but the problem seems to have returned again.
In brief, when cold, the car seems to run reasonably well. I say reasonably as its not really been used much over the last few years and can go 4 or 5 months between leaving the garage.
Anyway, I drove 15 miles or so in it the other day and it seemed to be running perfectly. I filled up with fuel, and straight away it starting feeling like it was misfiring again. I headed for home, but managed to narrow the fault down to a certain set of paremeters.
So, when accelerating, the car runs nicely and pulls as strong as it ever has. If you coast, again its smooth. You can accelerate through all the gears - no problems at all. However, if you try to maintain a set speed with a little bit of throttle, the engine seems to misfire, the car jolts, it sounds rough through the exhaust etc. Apply a little throttle and it all smooths out instantly, reduce throttle to maintain speed again and it misfires.
I put the car into third and went from 2000 rpm up to 3000rpm and it pulled smoothly, however at say, 2200rpm, if you try to maintain a speed with whatever degree of throttle is needed, the engine struggles. Drop a gear and give it a bootful of throttle and it rockets, maintain speed and it misfires/judders.
Anyone ever had this? I'm feeling like its going to be something simple like the vac advance on the distributor, or maybe its still a knackered ecu. Perhaps the timing is now out due to the distributor, or maybe its a fueling issue. I've done all the usual Lucas electical tests in the diagnostics document and everything seems fine.
Any ideas?
Thanks,
Dan.
Im with Keith on this one...It does sound like whats called a "Tracked" fault...i:e AFM...Throttle Pot Sensor...(TPS)...something that relies on a track for volts etc can wear and if the fault persists on a defined RPM then there is your weak spot..
I have seen a fair few that have the yellow wire broken..they are not repairable...new ones are expensive..Someon may have a spare if you are lucky...I gave mine away....
Cheers
Ziga
I have seen a fair few that have the yellow wire broken..they are not repairable...new ones are expensive..Someon may have a spare if you are lucky...I gave mine away....
Cheers
Ziga
To expand on what Zig says, the throttle pot is a potentiometer (variable resistor) that tells the ECU how wide open the throttle is.
The carbon track can wear out and ususally it will go first around commonly used light throttle openings.
When it wears out it will go open circuit at certain positions. To diagnose this, get a voltmeter and connect it between the centre connection and ground. Ignition on. Slowly rotate the throttle by hand, the voltage should vary smoothly. If the voltage jumps about erratically, you have your problem.
There are two type of throttle pot, the larger one is about 2 inches across. They can be repairable by disassembling and moving the slider off to one side a bit, it will give you a few thousand more miles use.
For my 350i I baulked at the cost of a new original one so I researched a bit and found a pot with 1 million rated operations (which actually only equates to about 60k miles). Only problem that it was electronic and went "the wrong way" i.e. throttle closed was 5V and open was 0V, so I had to add on a small linear inverter circuit.
It seemed to work quite well but it loses the look of originality.
The carbon track can wear out and ususally it will go first around commonly used light throttle openings.
When it wears out it will go open circuit at certain positions. To diagnose this, get a voltmeter and connect it between the centre connection and ground. Ignition on. Slowly rotate the throttle by hand, the voltage should vary smoothly. If the voltage jumps about erratically, you have your problem.
There are two type of throttle pot, the larger one is about 2 inches across. They can be repairable by disassembling and moving the slider off to one side a bit, it will give you a few thousand more miles use.
For my 350i I baulked at the cost of a new original one so I researched a bit and found a pot with 1 million rated operations (which actually only equates to about 60k miles). Only problem that it was electronic and went "the wrong way" i.e. throttle closed was 5V and open was 0V, so I had to add on a small linear inverter circuit.
It seemed to work quite well but it loses the look of originality.
Edited by adam quantrill on Monday 26th November 12:13
This might be what you need but is eyewateringly expensive:
https://rimmerbros.com/Item--i-EAC2670
which interesingly is also fitted to the Jag XJS although you will need to change over the connector from the old one.
https://rimmerbros.com/Item--i-EAC2670
which interesingly is also fitted to the Jag XJS although you will need to change over the connector from the old one.
Edited by adam quantrill on Thursday 29th November 14:47
Hi Everyone,
Sorry for the slow response – work has been busy this time of year so the poor wedge has been sitting in the garage ever since I posted in November.
Anyway, I had a eureka moment and made a huge amount of progress the other day. I’ll write the long winded solution to the issue I was having in a mo, but the short version is that the misfiring was due to a dodgy connection to the injector resister block that sits on the nearside wing.
Long version now – hopefully it will help someone else troubleshoot one day.
As per the recommendations, I checked the throttle pot voltages throughout its sweep and it all came back normal. As the car has sometimes been fine when cold, I made some jump wires up and ran them from the throttle pot and battery to inside the cabin, and connected a multi-metre. I got the car warm and observed that the pot was fine on a longish drive, even through the car was running badly.
The next thing I checked was all the HT lead connections to the cap and spark plugs. I thought I had found the issue when one of the leads (the nearside rear-most piston) didn’t seem to have a very good connection to a spark plug. Whilst most of the leads came off with a “click” when pulled, this one didn’t. When I removed the lead, a couple of small pieces of metal fell out - presumably these made up the little internal clip that grips the spark plug. Anyway, I pushed the lead on the best I could and started the car. Bingo! It ran perfectly! There wasn’t time for a test drive as it was now dark, so the car sat for a couple of days until I had time.
Test drive day arrived, and I started the car. It sounded a little rough, but not unusual for the cold temperatures. Out I went, and within a mile the car was running as badly as ever… I did a few more miles and it misfired constantly. I found somewhere to turn around and in a fit of annoyance and frustration I literally revved the nuts off the car by the side of the road before heading home. As if by magic, the car ran perfectly again! Home was about 10 mins away and I pulled up on the drive way with the engine running fine.
Still annoyed, I opened the bonnet and poked around for a bit. As I lent over and wobbled the suspect HT lead, the engine note changed and it was down on cylinders again, sounding rough. So it seemed there must be a dodgy electrical connection somewhere. With the engine still running I literally wiggled every connection, wiring run, terminal, wiring clip etc to see if anything changed. It didn’t. Then, just as I was checking the air intake hose, the engine started running fine again. This lead me to wiggle the wiring loom running to the injector resistor and instantly it affected the engine note! I disconnected it, closed up the female connectors a little and reconnected. Started the car and it was idling fine.
Test drive time again, and the car was 90% better. All the misfiring during normal driving had disappeared on the 1.5 hour test drive. Previously, after only a few minutes the car would be running rough so I genuinely think I found the most serious cause of the problems. I reckon that with the injector resistor being mounted on the wing, the rocking motion of the engine when revved would stretch/move the loom a little causing the intermittent fault. It’s the same reason the fault appeared/disappeared when I was playing around with the air intake and HT lead – me leaning over the wing probably moved the loom a little.
Now, the reason the car is only 90% better is that the engine starts feeling strangled when above 4500rpm-ish. It starts to misfire a little, is a little jolty and loses it power. However, I reckon this is going to be a separate tuning issue, ie the timing is out, weights in the distributor stuck, fuel pressure, blocked fuel filter etc.
Since I moved house about 5 years ago the car has sat around and done hardly any miles, especially as it developed this engine fault. In fact, I think that all of the issues I have had over the last few years have been caused by a lack of use. My best advise to people at the moment is to take the car on a long run every month or so to keep things from seizing, corroding and getting damp. Before the 1.5 hour test drive the other day, so many things on the car didn’t work. The wipers wouldn’t move, the windows wouldn’t wind up without a huge tug, everything squeaked or rattled and it felt like a car that was way past its best. During the drive, everything gradually started working again and it came back a totally different car.
So yeah, huge progress after so many hours of frustration caused by a lose connection. Thanks everyone for all the advice in troubleshooting.
Dan.
Sorry for the slow response – work has been busy this time of year so the poor wedge has been sitting in the garage ever since I posted in November.
Anyway, I had a eureka moment and made a huge amount of progress the other day. I’ll write the long winded solution to the issue I was having in a mo, but the short version is that the misfiring was due to a dodgy connection to the injector resister block that sits on the nearside wing.
Long version now – hopefully it will help someone else troubleshoot one day.
As per the recommendations, I checked the throttle pot voltages throughout its sweep and it all came back normal. As the car has sometimes been fine when cold, I made some jump wires up and ran them from the throttle pot and battery to inside the cabin, and connected a multi-metre. I got the car warm and observed that the pot was fine on a longish drive, even through the car was running badly.
The next thing I checked was all the HT lead connections to the cap and spark plugs. I thought I had found the issue when one of the leads (the nearside rear-most piston) didn’t seem to have a very good connection to a spark plug. Whilst most of the leads came off with a “click” when pulled, this one didn’t. When I removed the lead, a couple of small pieces of metal fell out - presumably these made up the little internal clip that grips the spark plug. Anyway, I pushed the lead on the best I could and started the car. Bingo! It ran perfectly! There wasn’t time for a test drive as it was now dark, so the car sat for a couple of days until I had time.
Test drive day arrived, and I started the car. It sounded a little rough, but not unusual for the cold temperatures. Out I went, and within a mile the car was running as badly as ever… I did a few more miles and it misfired constantly. I found somewhere to turn around and in a fit of annoyance and frustration I literally revved the nuts off the car by the side of the road before heading home. As if by magic, the car ran perfectly again! Home was about 10 mins away and I pulled up on the drive way with the engine running fine.
Still annoyed, I opened the bonnet and poked around for a bit. As I lent over and wobbled the suspect HT lead, the engine note changed and it was down on cylinders again, sounding rough. So it seemed there must be a dodgy electrical connection somewhere. With the engine still running I literally wiggled every connection, wiring run, terminal, wiring clip etc to see if anything changed. It didn’t. Then, just as I was checking the air intake hose, the engine started running fine again. This lead me to wiggle the wiring loom running to the injector resistor and instantly it affected the engine note! I disconnected it, closed up the female connectors a little and reconnected. Started the car and it was idling fine.
Test drive time again, and the car was 90% better. All the misfiring during normal driving had disappeared on the 1.5 hour test drive. Previously, after only a few minutes the car would be running rough so I genuinely think I found the most serious cause of the problems. I reckon that with the injector resistor being mounted on the wing, the rocking motion of the engine when revved would stretch/move the loom a little causing the intermittent fault. It’s the same reason the fault appeared/disappeared when I was playing around with the air intake and HT lead – me leaning over the wing probably moved the loom a little.
Now, the reason the car is only 90% better is that the engine starts feeling strangled when above 4500rpm-ish. It starts to misfire a little, is a little jolty and loses it power. However, I reckon this is going to be a separate tuning issue, ie the timing is out, weights in the distributor stuck, fuel pressure, blocked fuel filter etc.
Since I moved house about 5 years ago the car has sat around and done hardly any miles, especially as it developed this engine fault. In fact, I think that all of the issues I have had over the last few years have been caused by a lack of use. My best advise to people at the moment is to take the car on a long run every month or so to keep things from seizing, corroding and getting damp. Before the 1.5 hour test drive the other day, so many things on the car didn’t work. The wipers wouldn’t move, the windows wouldn’t wind up without a huge tug, everything squeaked or rattled and it felt like a car that was way past its best. During the drive, everything gradually started working again and it came back a totally different car.
So yeah, huge progress after so many hours of frustration caused by a lose connection. Thanks everyone for all the advice in troubleshooting.
Dan.
Thats really good news...you have to be like you have ...Methodical, earths and connections are always good to check...I had the same issue with the resistor pack and put two large cable ties round the plug to unit..
It is so difficult to diagnose some of these mis-fires as some like what you have happens with other parts when they fail...I would clean all three earth points...the main one is down on the N/S suspension turret...then there are two on the rear of the N/S rocker cover.
Also remove the ECU plug, clean up the male and female terminals...bit of contact cleaner with a fine emery board..push the plug firmly back on until you hear a click...again I have two large cable ties round mind as it did come loose a minute amount but caused havoc....
Replace plug leads with a good standard range rover set with an extra long king lead...wipe out the distributor cap with some WD40 contact cleaner and a clean cloth..You can clean the rotor arm with some auto-sol or something...dont use emery paper!..Put a tiny amount of oil on the inside of the body of the rotor arm.....You could remove the plastic cover on the distributor and spray a generous helping of contact cleaner in there...leave for a hour or so before putting back together.
You could try retarding the timing a tad....
Make sure your air filter is clean or new and the breather is clear on the N/S rocker...the mushroom comes out a lot easier with a warm engine...also check the condition of your flame trap as when clogged this can have a suffocating effect on your engine...
Hope this helps
Ziga
It is so difficult to diagnose some of these mis-fires as some like what you have happens with other parts when they fail...I would clean all three earth points...the main one is down on the N/S suspension turret...then there are two on the rear of the N/S rocker cover.
Also remove the ECU plug, clean up the male and female terminals...bit of contact cleaner with a fine emery board..push the plug firmly back on until you hear a click...again I have two large cable ties round mind as it did come loose a minute amount but caused havoc....
Replace plug leads with a good standard range rover set with an extra long king lead...wipe out the distributor cap with some WD40 contact cleaner and a clean cloth..You can clean the rotor arm with some auto-sol or something...dont use emery paper!..Put a tiny amount of oil on the inside of the body of the rotor arm.....You could remove the plastic cover on the distributor and spray a generous helping of contact cleaner in there...leave for a hour or so before putting back together.
You could try retarding the timing a tad....
Make sure your air filter is clean or new and the breather is clear on the N/S rocker...the mushroom comes out a lot easier with a warm engine...also check the condition of your flame trap as when clogged this can have a suffocating effect on your engine...
Hope this helps
Ziga
Yeah good news Dan.
As you know by now there are a lot of connectors involved with the ECU and any of them failing can spoil your day, worse probably is when they are intermittent.
I also tend to pack mine with some grease now to keep the moisture out, after cleaning and tweaking them for a good connection.
As you know by now there are a lot of connectors involved with the ECU and any of them failing can spoil your day, worse probably is when they are intermittent.
I also tend to pack mine with some grease now to keep the moisture out, after cleaning and tweaking them for a good connection.
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