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Hooked up OBD reader and got readings. Now I wonder if some OBD wizard can look at the data for me and form some sort of diagnosis from them? It looks to me as if the fuel trims are too high (total 15% on both banks at 3300RPM), indicating over-fuelling. But why does the Long Term FT wander around so much? Sitting in the car in an open barn gave me a headache. Deffo not right
I understand this could be caused by an air leak on the hose after the MAF. How tight should the junction be between the hose and the throttle body? Mine rocks around a bit.
I will attach screenshots to a second post if I may
Last edited by jayartibee; May 13, 2017 at 12:39 PM.
If you're still getting the error codes it means there's a poor connection, or no connection, to the MAF/IAT sensors. If the error codes did go away, I don't know... There's a table somewhere, can't remember if it was in the shop manual, of expected MAF rates for certain RPM's, both idle and steady higher rpm's.
I don't know about the high trims, it definitely means it's sending more fuel than usual, and such a high positive is excessive.. I thought that vacuum leaks were supposed to affect trims more at idle than at higher RPM's, unless whatever is leaking is "loose" and opens up a bit more when rpm's are higher, allowing more air in?
As I mentioned in your thread on the UK site earlier, the MAF sensor was the first one to be checked / suspected.
Although all above readings are static, the above confirms IMO that your MAF sensor has a problem.
Either dirty, a connection problem, but most likely dying.
The readings at higher rpm are much lower than they should be.
The result is that the MAF sensor reads less air than which actually goes through.
Consequently, the ECU initially gives less fuel than needed before the combustion.
Then, your CO sensors sense that your burned mixture is too lean, and compensates this by adding fuel over the standard amount, hence your 'plus' values'.
My approach should be:
1. Clean / spray the wires of the MAF sensor carefully to clean them,
2. If that does not work, check the connector and the pins of the connector carefully, bend them a tiny bit if needed for good contact,
3. If that does not work, replace the MAF sensor.
After that, you can do some readings again, and see if the problem is solved, or if you have to dig further.
But I guarantee you this is a big part of your solution.
Btw, you will not be the first one with a broken MAF sensor, I notice there are more owners running into this recently.
Last edited by ericjansen; May 13, 2017 at 06:36 PM.
I'm not sure you can put much stock in your MAF readings if you are only running the RPM's while stationary as there's a load factor missing that only occurs if the car is moving. (even on a dyno the load is somewhat reduced because of a lack of wind resistance and the lower rolling resistance on the tires although a good dyno can add for that)
Your MAF reading at idle (686 rpm's) is 4.99 g/s and the Jag target is 5 g/s...close enough for gov't work. At 2250 rpm's with no load your MAF reading is 10.88 g/s against a target value of 17 g/s so that's suspect but also 250 rpm's shy so run that sequence again but at 2500 rpm's instead.
At 3260 your pulling 15.57 g/s against a target of 39.3 g/s but that target is for 1500 rpm's under LOAD and sitting in the barn isn't the same thing. Can someone ride with you and use the phone to get readings at various RPM's while you drive?
I think I would replace the MAF, clean the the throttle bore and plate, tighten all fittings to assure no leaks, check the seal at the dipstick, run a can of a good quality intake/fuel cleaner. And drive it for a while (unfamiliar with UK laws: can you drive it with a failed MOT?). How old are the plugs?
For real cheap you can get yourself a device that records as a graph a sensor data as you drive around . Something may show up with this ELM327 causing the engine regulation off and save you some money and time in shop visits . There is a Jaguar TSB 303-43 and 47 that has a troubleshooting alogarithm tree even though it may not be specific to your series of engine as this is for the V8 AJ26 ,the same regulation applyes with some exceptions like VVT equipped not having an EGR a valve . You can take the graph and post it and maybe someone can see something not scean before .
You can DIY check LTFTs e.g. using elm327. Yours way back at higher RPMs are too high.
Check fuel pressure.
If the previous MoT was OK, are the fails now dramatically different or just a bit and it scraped through before? (This may help figure of it's a part gone bad or just further deterioration.)
May be worth checking the cats are OK.
Also, it is worth being sure that required servicing etc has been done - especially for air filter, fuel filter & spark plugs.
Well gents - I took the Jag to a knowledgeable specialist with a proper Jag Autologic machine and he said everything was fine apart from the upstream sensors which were outside the correct parameters. He recommended starting with those.
So - Denso only? Bosch? Aftermarket?
And a 22mm O2 sensor socket I guess - looks a pig of a job
Well gents - I took the Jag to a knowledgeable specialist with a proper Jag Autologic machine and he said everything was fine apart from the upstream sensors which were outside the correct parameters. He recommended starting with those.
So - Denso only? Bosch? Aftermarket?
And a 22mm O2 sensor socket I guess - looks a pig of a job
Yep I'd go with the O2 sensors, heater element failing?
I use either Teng or Franklin O2 sockets, both are slotted and around £20.
There's a thread on here about using s/h X type sensors (cheap, off ebay) but not sure if they're upstream or down, you'd have to run a search. I always use OE parts but many have used a generic item off Amazon, Bosch I understand, someone may chime in with a link.
Sorry to join your thread so late, but looking at the symptoms you've posted, I'm wondering if a further investigation of the diagnostic trouble codes might be worthwhile.
Since you haven't shared the year of your car, I don't know if your engine is an AJ26 or AJ27, but here are the Jaguar definitions from the 1998 AJ26 DTC Summaries guide:
Looking at the Possible Causes column, I notice that both codes can be flagged due to a problem in the wiring between the ECM and the MAFS and the ECM and the IATS. On normally-aspirated X308s the only IATS is built into the MAFS, so one possibility is that corrosion on the terminals of the ECM or MAFS electrical connectors could add resistance to the circuit or short between pins, flagging both DTCs. So it might be worth checking and cleaning those connectors.
Since signals of both the MAFS and IATS are directly involved in the ECM's fueling decisions, a malfunction in these circuits could definitely affect your fuel trims. So before you buy oxygen sensors, please check and clean the connectors at the MAFS and the ECM.
By the way, regarding oxygen sensors, in my own not-so-humble opinion it is prudent to use the same brand sensors as the engine management system, which in the X308 is Denso.
thanks Don - although I put in a replacement Denso MAFS/IATS back in June which had no effect - and the contacts seemed fine. Autologic and other diagnostics aren't picking up any MAFS errors
understanding OBD data
