Help with MAF readings
 

Hi all,

I'm trying to figure out what is causing fault codes P0172 and P0175. I have changed my coolant temp sensor as part of changing the thermostat housing as I had a bad coolant leak but I now have these fault codes. I had a rough idle and engine vibration and rich running which is why I replaced the housing incase the coolant leak or a faulty temp sensor was the cause. Even after changing this, I still have an engine vibration at about 1400 to 1800 RPM. When I drive the car over that rev range there is not engine vibration and the car is powerful and quick. It just runs rough between those revs and is now throwing 'Restricted Performance' as soon as I start the car and the car is running really rough at idle or when started cold.

I'm now checking my MAF sensor incase the issue is being caused by that. Dirty or faulty perhaps.

However, I don't know what readings I should be expecting to see. The readings I've got so far, at idle and once the car has warmed up to operating temperature, seem to fluctuate. I'm not sure if that is how it should operate. I would expect that the readings would fluctuate a little but the readings I'm getting seem to vary quite a lot and fluctuate at the same time that the revs fluctuate.

Can any of you guys comment on what mass air flow rate (g/second or lb/minute) readings you are getting when your cars are running at idle and at temp? And do you see any fluctuation or a constant reading?

I have captured the live MAF readings data which I will upload once I get them off my tablet.

Thanks,

Chris

With the codes the car stores lots of "freeze frame" data to help you see why - things like engine load, speed, rpm. Might be good clues!

Thanks JagV8. I'll grab the Freeze Frame data logs as well.

The below are some of the readings when the car is idleing. You can see that the RPMs are clearly jumping around along with the MAF readings.

Thanks,

Chris

https://cimg4.ibsrv.net/gimg/www.jag...ef62eec186.jpg
RPM versus MAF readings at idle and when car is fully warmed up.

https://cimg0.ibsrv.net/gimg/www.jag...eb4662c8c4.jpg
RPM, Coolant temp, MAF and Air Intake Temp readings at idle and fully warmed up.

https://cimg2.ibsrv.net/gimg/www.jag...b2348cf218.jpg
RPM, Coolant temp, MAF and Air Intake Temp at idle and warmed up.

Now going to get the MAF out and do some voltage readings before in case this is a connection problem.

Thanks,

Chris

Hi JagV8,

Here is the freeze frame data whilst driving in traffic.

https://cimg5.ibsrv.net/gimg/www.jag...e8421b4b0e.jpg
Freeze frame data


Thanks,

Chris

Is that freeze frame when the DTCs flagged? Doesn't look to be.

It's currently got 'Restricted Performance' on the dash but no fault codes or DTC's pending nor stored. The EML is also off at the moment but the runs rough at idle and vibrates at the same RPM as before.

If you cleared the codes you may now be in Catch-22 where the OBD monitors cannot set and so most codes are suppressed.

If so, diagnosis gets tough and you may need to go back to guessing e.g, try a smoke test, swap parts, etc.

But do bear in mind that by law many codes can only be flagged after 2 warm ups.

Thanks JagV8.

I've been looking through the MAF readings again and I'm pretty sure my readings are way too low.

I've done some calculations and it seems that I should be getting approx 4.2 G/sec at 500 RPM.

Now my car does not idle at 500 RPMs. So at 648 RPM (which my car very roughly idles at) I am getting 4.69 and I should be getting more like 5.4 G/sec.

At 1260 RPM I get 5.8 G/s and should be getting approx 10.5 G/s.

And at 1480 RPM I'm getting 7.2 G/s and should be seeing 12.4 G/s.

So I'm going to try cleaning the MAF first and see what that does and I'll check the connector on the MAF as I've read some owners having issues with the connector causing rich running conditions due to inconsistent connectivity.

Thanks,

Chris

i was informed a while back the 4.2 STR and XJR MAF range at idle is between 3 and 5 G/S
idle being 650rm . I Imagine the NA will be the same at idle

Hi Chris,

I think you may be missing the diffence in units in which MAFS readings can be expressed. From your freeze frame, your MAFS reading was 4.66 pounds-per-minute (lbs/min) at 1975.5 revolutions-per-minute (rpm). This is equal to 2113.74 grams-per-minute (g/min) or 35.229 grams-per-second (g/sec). My impression is that this is plausible and not low to any significant degree.

However, your graph of the MAFS signal certainly appears erratic. I assume you have cleaned the MAFS/IATS elements and electrical connector? Have you cleaned the ground point referenced by the ECM, on the inner fender inside the right engine bay compartment where the cabin microfilter and ECM electrical connector are located?

I have to get to bed, but I note that your STFTs are Lean and your LTFTs are Rich. I'm pondering these numbers while viewing your O2 sensor readings.

Restricted Performance with no DTCs could suggest an electronic issue somewhere. Does your scan tool have the ability to view Network (U-prefix) and Chassis (C-prefix) codes? I also like JagV8's suggestion that you may be in a Catch-22 until DTCs recur.

Cheers,

Don

Thanks Don and Datsports. I haven't yet had a chance to look at this further. The car now is sat on the drive as it stalls after starting and runs very rough up until it stalls. It will only run for about 2 minutes and then stalls. Going to look at this today and hopefully it will be something simple.

Good hunting:icon_hunter:

If you can get it properly hot (by driving) i.e. so the cats are hot, see what the trims (especially LTFTs) are at idle then rev to about 2500 and see what they are then.

If the LTFTs start quite big but drop at 2500 you've an air leak and when bad enough you get stalling. The MAF would then not be likely to be #1 suspect.

I finally got to look at this problem. Tested the MAF voltages and continuity and it all seems to be fine. It has good ground and the right voltages.

So I cleaned the MAF sensor and also cleaned the connectors with electrical contact cleaner.

Started the car and it ran rough as normal and displayed the 'Restricted Performance' and no EML. After about 5 minutes of running at idle the 'Restricted Performance' disappeared and the car ran perfectly. Before the clean and before these problems you could feel the engine at idle. The engine was now smooth at idle and you could see that the engine was not vibrating. It was running much smoother and almost completely silent when in the car.

I took it for a drive and it all seemed ok. I drove it for about 30 or 40 minutes of mixed driving. The car didn't hesitate and acceleration was immediate.

I had no codes and the 'Restricted Performance' warning was off.

I went out in the car this morning and as soon as I started the car the 'Restricted Performance' displayed again with no fault codes. The EML was off. I scanned the car for codes and it showed P0175 and P0172 as pending codes. I cleared them and the RP disappeared for a few seconds but then comes back.

So I drove it about 10 miles and the RP stayed on all the time and drove really rough. Stopped the car and went shopping for a few minutes. Restarted the car and no RP warning. It was off.

The car then ran perfectly and was smooth and quite again. I drove the car for about 20 minutes and still no RP warning. I got the car home and switched it off and then back on again and no RP warnings.

It looks like the car is now throwing the RP when the car is started when cold and until the car has reached full temperature. It was throwing the RP all the time before I cleaned the MAF. Once it's at temp it looks like the RP goes off and the car runs perfectly.

Once it's at temp it looks like the RP goes off and the car runs perfectly.
Sounds like me most mornings when i wake up:o

So these are the readings from the car for fuel trims. This is when the car is fully at temp.

https://cimg2.ibsrv.net/gimg/www.jag...7751d70ec0.jpg
Fuel trims at idle

https://cimg9.ibsrv.net/gimg/www.jag...925fdd7624.jpg
Fuel trims at 2500 RPM - the drop off at 62 is when I released the throttle.

Yes it's looking that way WIngrider.

Thing is that by clearing the codes you've cleared the OBD monitors when what you want is to see if those rich codes flag and if so see why.

Clearing codes is stopping you getting useful data.

Give it a chance to learn what's happening, and see if all the OBD monitors manage to set.

Then give it a chance to flag codes.

Thanks JagV8.

So I need to let it throw the fault codes and then see what the fuel trims are whilst the codes are not pending? Is that right?

The car is definitely running much better now that I have cleaned the MAF.

Whilst I was there I did a vacuum leak check (using carb cleaner). I sprayed all over the air intake tubes/connections, air filter housing, throttle, egr, brake booster lines, oil return lines, injectors, all around the manifold and the RPM did not change at all. I've also done a smoke test and found no leaks.

Vacuum leak on my 04 XJ8, was those eight pesky gaskets, in the intake manifold.
No issues except the C E light would come on.

So the car kept going into restricted performance mode still when started from cold. I've been checking for fault codes and there was nothing showing - not even pending codes. However yesterday morning when it went into RP on starting it was running even rougher than before. I checked for fault codes and it had P0207 as pending. I've cleared the pending code and it now keeps throwing P0207 as pending every time I start the car from cold. If I drive the car for a while with RP and then stop and start the car the codes seem to clear and RP disappears which I find strange. I took it for a long drive yesterday and after a long amount of driving it did go back into RP and then actually threw a registered fault code - again P0207. I've started the car this morning and it has once again gone into RP with the pending fault of P0207. I drove the car to work, filled up with fuel oh the way and then started the car and no RP - it had gone. I drove the next 50 miles with no RP and the car drove perfectly (apart from the engine vibration still at about 1400 RPM).

Since cleaning the MAF, when the RP is off, the car does drive so much better. It does not seem to hesitate on acceleration, it no longer lurches in cruise control and the engine at idle is now almost silent and with almost no vibration.

Just now got to get out the multimeter and test that injector and harness. I had an injector fail a while ago, the one next to this one in fact, injector number 5. When that went it was an open circuit but displayed the fault code all the time. This problem seems to go away when warm possibly so it could be the injector starting to fail.

If it is a failed injector then it would not explain the rich running on the other bank but I'll deal with this first and then look at possibly replacing those intake gaskets. I might do them at the same time, it's just if I have enough time to spare to do it all at the moment.

Thanks,

Chris

Hi Chris,

Here are the definition and listed possible causes of P0207 from the 2003.5 DTC Summaries:

https://cimg8.ibsrv.net/gimg/www.jag...4a0adeb0c7.jpg
https://cimg3.ibsrv.net/gimg/www.jag...bf628b120c.jpg

Based on the above, you might start by checking the electrical connector and wiring to the injector at cylinder 7. If you have a noid light or if your meter has a duty cycle setting you could check for a plausible drive signal at the injector connector while the engine is running. If that looks good, you could check the DC resistance across the injector pins and compare it to other injectors on that bank.

Cheers,

Don

Hi Don,

Thanks for this. Yes I'm going to start with checking resistance on the injector itself. I did this last time when I had an open circuit on injector 5. I still have the OHM readings from then for the other injectors so I know what to expect. I think they were 14.7 or 14.8.

If the injector resistance is ok then I'll start checking the connector and the harness itself.

Hopefully it's just the injector. If it is then I'll check the cabling further when I'm in there replacing it just in case there is some short occurring in the harness.

Thanks,

Chris

Hi all,

The problem is definitely injector 7 is open circuit (no resistance across it). The fault code p0207 is now present all the time and the RP is on all the time now. I think the injector has been partially working and starting to fail which is why the faults and the RP were intermittent. Just ordered a new injector and spare o-rings for the other injectors. I replaced injector 5 on the same bank last year so at least I know how to replace number 7 and what to expect. Interestingly, I have been driving the car with the faulty injector and I have not had any rich fault codes yet at all on either banks since cleaning the MAF.

I'll keep you all updated once done and let you know if it clears the RP issues.

Thanks,

Chris

Hi all,

Success :icon_woot:

I replaced the injector #7 at the weekend and the car now runs without any fault codes. RP and EML are off and I took the car for a drive for it's MoT which it passed. The car now drives brilliant and there are no rich fault codes anymore either. The car starts great, first time and does not rough idle anymore either.

I'm going to take it for a long run tomorrow to work so hopefully all will be good and I'll get a chance for it to stretch it's legs.

Hopefully my MPG will also be better as well now that the rich codes are gone and that the car is not running in RP anymore.

I'm not sure if this was the cause of the rough idle or if cleaning the MAF helped with that.

Thanks for all the support with this guys.

Cheers,

Chris

Hi all,

Well my rough idle is back when the car is started from cold and the engine vibration at about 1400 to 1800 RPM is also back. It's odd because the car ran great for over a week after replacing the faulty injector.

I've got no fault codes or rich codes registered but there is clearly some reason for this problem to return.

I'll check fuel trims to see if there is any difference from before the injector was faulty.

Looking like it might be the manifold gaskets as these are pretty much the only thing I haven't replaced.

Thanks,

Chris

Mine still ran fine, but the check engine light kept coming on.

Replace something hoping for the best, all parts are suspect turn light off.

Drive a hundred miles or more sometimes, a few blocks till on again it went.

Runs the same after finally fixing it, but no more light, & it passed the emissions test.