But then tricking a MAF into thinking that more air is going in is one point

BUT,

What if the ECU has a limited range over which it can add fuel?

If the fuel trim is already as rich as the ECU can possibly make it at the rev point, and if there is a limit on the airflow at that rev point, then how can the ECU add more fuel?

Of course if there is plenty of leeway in the ECU, then it should be able to do it.
 
But then if there was plenty of leeway.........

wouldn't the ECU have done it already?

Problem solving is a series of logical steps of IF ......THEN repeated over and over based on hypotheses.

I can provide many IFs and THENs, but if you don't like my IFs, please just ignore them, don't get upity or upset or rude or patronising, because each of our experience is different and the value of our "contribution" will only be determined at the end when the problem is solved.

IF one of my IFs is wrong, then I am not wrong, and the hypothesis that I proposed is not wrong it is only not applicable to this particular problem.

The outcome of the hypothesis is a THEN, and the symptoms fall into this category
There is no "bad" hypothesis, it is applicable or not.

For each problem we have to slowly get feedback from the "problem owner" to narrow down the IFs and THENs

I might be able to provide many of the THENs, but sometimes tying up the IFs with the different THENs is quite complex with the number of different permutations of what can go wrong.
 
Raving Man said:
Me not making sense?

This last test doesn't make any sense to me at all, but I accept I can be dim, a little slow, but please be patient.

Why not find the airleak? Loose throttle bodies and manifolds are an obvious culprit.

Let's open the throttle / idle control and restrict the flow before the MAF.
What happens? - MAF comes under vacuum - not normal, but air flow will increase because it is at a lower density (lower pressure), but what will happen to the cooling of the MAF (hot wire) or deflection of a vane type MAF.

The hot wire will not be cooled so well with the lower air density.
I can't say about the vane type MAF except the mass of air per second will not be any different. How much would the kinetic energy of the air change though?

What would happen to the temperature of the inducted air?

It's an interesting trick if eightinavee would actually explain the theory behind it.
Click to expand...
I was making the point that blurting out multiple posts of stuff that looks like you just found it off a Wiki site,does not help.With any diagnosis you need to work with data that you have - not just conjour up loads of possibles.Now that Bill has provided some really useful data we can work with it.
The point of partially blocking off the inlet to the maf is that the same amount of air will go into the inlet - but at a higher speed over the maf sensor,fooling it into thinking there is more air going in than actually is.Then the ecu can use a different part of its fuel map allowing a wider injector pulse width.Hopefully enough to get the sensors to switch up rich and start cycling.It is a useful trick esp with Motronic Thor v8's which seem to suffer from this.
It tells us that the ecu can respond to a lean signal and it also tells us that the oxy sensor heaters are working properly as there is no way they would be hot enough to switch at idle without help from the heaters.
I am not trying to down anyone,just to help sort out a problem that has gone on too long.I have seen and dealt with problems on DII's like this since they came out and in almost all cases its down to a low maf reading.
 
Now that's what I call a useful explanation!!

I would be interested to know.....with all the low MAF readings, what are the different causes that you have found that cause the low MAF reading. This point is coming back to an earlier post, where you might have a symptom, but you need to get to the root causes.

Can you list them out?

With regards to Wiki, I noted that Bogwyth said that they were his original sensors and that the engine (long engine) was rebuilt. If you look at my posts, many were actually saying about the age and failure rate of different components, and this was actually from personal experience.

With regards to data, you can never have too much if you are able to work through it all very rapidly, and you can use many problem solving and statistical techniques such as Taguchi analysis, Principle Component Analysis, or just good old experience.

With solving different problems, you get different owners who have different abilities and motivations. Sometimes part of the "brainstorming" stuff throws up answers that actually enables you to better judge what level or experience others have, and how to help them better, or give them ideas that they might use sometime, if not now.

I am learning from your experience, as I hope you might from mine, and then others that might have a similar problem or even slightly different, because you do get different causes giving the same general symptoms - see TPS earlier.

Perhaps I pitched my points a little lower than I could have, oh well, must try harder!
 
Right idle 6.8g/s, 3000 revs 27.6g/s.

Switched MAFs gave the same results but initially the 02 sensors appeared to be switching for a 20-30secs from virtually zero to .0859 then they went back to the same outputs as before.
 
Part blocking the MAF resulted in figures up to:

Bank 1,1: 0.945
Bank 1,2: 0.900

Bank 2,1: 0.915
Bank 2,2: 0.915

Blocking it completely resulted in stalling :D
 
Mogwyth said:
Part blocking the MAF resulted in figures up to:

Bank 1,1: 0.945
Bank 1,2: 0.900

Bank 2,1: 0.915
Bank 2,2: 0.915

Blocking it completely resulted in stalling :D
Click to expand...
Are these oxy sensor voltages ?
The maf readings when converted to KG/Hr are well within the parish,the ecu should be more than able to cope with them.So I think we can look elsewhere.In your previous post where you quoted the maf readings you say about the oxy sensors switching from nearly zero to 0.085v - this isnt switching,its still a lean signal,it needs to be .8v, not 0.08v.
I'm wondering from this if the oxy sensors are being heated,you could try connecting a plug to a lead from either bank and laying them on the rocker covers to run the engine on 6 cyls.This should mean the unburnt fuel on both banks will give the oxy sensors a horribly rich mixture to report,which will make the short term trims go all the way negative.
 
Yes they are O2 voltages, the MAF flow only changed marginaly. Sorry in that previous post it should have been 0.859, so they will switch.
 
Raving man
Question one why egr?
Two why multiple posts why not edit old post or answer with thought?
Three apart from giving loose ideas and confusing the chap one idea at a time?



Bill let's start simple what's the updates on the mechanical?
With so many of the electrical outputs being ok based on your reading no offense then it is either a bizarre sensor fault or mechanical at a guess unless I could plug in and have a play with my testbook
 
No offence taken Stu. Simon the guy that fitted it is away at the moment (bereavement) so no answers on the mechanical side.

I wouldn't mind you having a look at it, send me a pm with a quote based on meeting up in Shrewsbury.
 
vougese39,

EGR problems are common on many engines, typically the EGR valve itself gets stuck open, feeding in too much exhaust gas. The symptoms of too much EGR are virtually identical to an air-leak.

I was trying to look up the EGR system on this engine, but have had difficulty in finding info - starting to wonder if it has it - bit of an assumption on my part.

I'm more familiar with the old twin SU V8s, where problems are easier to sort out, but experience from other ECU controlled engines and research experience gives a bit of leverage to cope with most things.

I have edited old posts, and given some thought, but it takes a few seconds to read something, and if someone is asking questions here they can obviously sort out the wheat from the chaff and take what info they need. I've found that sometimes you can write something quite detailed and well thought out, but then the log-on times itself out and you lose what you have done - hence the multi-reply method.

I have used the same technique with others and they didn't mind at all, they just checked all the suggestions and one bloke was absolutely thrilled when he finally got his car working better than it ever had, when he was completely stumped.
 
With heated O2 sensors, could you try the old probing trick in the sensor connector and test for voltage on the sensor heater wire. You would need to do this carefully so you don't short the heater voltage to ground/0V.

Just another suggestion to check the sensor function. See if you can link the function with what Testbook says what they are doing - if it can tell or not.
 
Quick round-up particularly for anyone new to the thread:

Vehicle has a fully reconditioned 4.6 long engine fitted running on 4.0 map.
Symptoms:
Fault codes. Only a non relevant SAI code P0304.
Fuel consumption increased.
Hesitancy between 1250-2000 revs.
Won't go closed loop.
O2 sensors not cycling.

Replaced (all new genuine parts):
ECU
Front & rear O2 sensors
ECT Sensor
MAF

Readings:
MAF at idle: 6.8gms/s or 24.48kg/hr.
O2 sensors below 0.1v, will only rise to over 0.9v if air flow to MAF restricted.

Other issues found:
Throttle body loose - tightened bolts.
Missing jubilee clip on small air hose - replaced.
 
OK,so the oxy sensors can switch and the maf is seeing enough air.Yet the short trims are going all the way positive - that doesnt really make sense if they are switching rich while the trims are increasing on the way up to going open loop.
My only other thought at the moment is that the two injector looms that piggyback into the petrol injectors have been swapped bank to bank.It would be worth trying them the other way round - even if the red bands on the plug and sockect are together.(Think thats how Romano looms are tagged from distant memory)
Other than that getting Stuart to put a fresh set of eyes over it using a tool that we can be 100% sure of the answers has got to be a good move.
I'm too far away and I gave up mobile work about 2 years ago......
Raving man - DII Thor engines dont have egr.
 
Houston I think we may have a problem. The remains of Fuse 2 that feeds; Purge Control Valve, CMP Sensor, MAF sensor and 02 sensors. But it's still intact! What on earth could do this without blowing it? Time to get the wiring diagrams out:(

017.JPG
 
Ouch that looks hot!

Is the fuse rating to what it should be? or has someone swapped it for a higher rating?

Once you know what it should be feeding, you could try switching the ignition on, but not to start, then with an Ammeter in series with an appropriate fuse, disconnect each of the components that the circuit supplies.

That way you might be able to tell either if it is the component or the wiring, but you won't necessarily be able to say which. If you know the current draw specification for each of the components, then you can check that the change in current is as it should be for each component.

I have heard that sometimes O2 sensor connectors can breakdown. You might be unlucky with the sensors themselves, with a wiring fault on the sensor itself - yes, eventhough they are new. Do not make any assumptions that things don't fail when they are new. I gave you an example about coils, another one I have had personally was an oil filter - an oil filter you say? Yup, somehow the manufacturer hadn't put it through the process for putting a thread on the metal plate that screws the damn thing onto the engine - how the hell does that happen?

With the O2 sensors, if you have the old ones that have failed or did you change them before they actually failed? You could swap them over to the old ones, just by unplugging and plugging in the old ones and see what happens.

If the O2 sensors started to cycle, but then failed, it might be that the failure is in the sensor itself, where a short only happens when the things get hot - bad insulation.

What I have written here also applies to all the other sensors linked to that fuse.

If that has happened to the fuse, you might be looking for some wiring or a connector that doesn't look too much different to the way that fuse looks.

Thanks eightinavee, odd bits of info re. EGR help for future reference.
 
Last edited:
I was going to relate one bit of experience from someone else, who I spoke to in our 4x4 group, he went on a course by some car company about fault finding. He said that the company had set up an intermittent fault where they had cut through a fuse blade, such that the continuity was intermittent - what sick minds think up these things to torture their students? Oh, well cars seem to be able to come up with just as fiendish problems, without any thought at all.
 
On the LPG system, some installers are told not to cut the O2 sensor wires.

Has someone done so?

This is following on from eightinavee's thoughts.
 
Correct fuse, put a new one and ran the motor till up to temperature fuse didn't seem to get warm, but that may be because whatever caused the problem has shorted right out.

Even if they have hacked the O2 lines, it would have been like it before we replaced the engine and this fault didn't exist then.

Cheers
 
Very odd, it appears the someone has joined the wire that feeds the MAF to the Wire that feeds the O2 sensors, both wires have been stripped back without cutting and crimped together and taped with insulating tape! It seems to serve no purpose to me.
 
You must log in or register to reply here.

Similar threads

R
2000 Thor 4.6 fuel/starting problems
Replies
5
Views
399
richardtamps
R
300bhp/ton
P38A Vale block removal??
Replies
5
Views
751
Rubberknees
Rubberknees
H
Discovery 1 MAF 14 CUX
2 3
Replies
56
Views
2K
AllanWorms
AllanWorms
S
FL2 starting problems
Replies
9
Views
874
Scaz93
S
thebluelandy2363
Tax?
Replies
3
Views
286
Firebobby1
Firebobby1