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Car Forum / Ford / Ford Focus / May 20072001 Focus 1.6 Zetec engine, 60K miles: MAF sensor
I've been hunting around trying to find this so I can clean it, and I understood it is supposed to be located on the air intake hose. The only thing I can see that could be it is down behind the alternator on the very end of the manifold (two torx bolts + wiring harness), which makes the job quite a bit harder. Is this the right part or am I mistaken? I'm trying to sort out a problem which not just irritating but potentially dangerous- sometimes when dipping the clutch the idle drops down so far it cuts out, which is obviously hair raising when you've commited yourself to pulling out in traffic! The idle is generally a bit ropey (neither feels nor sounds smooth) and the rpm is inconsistent, though usually hovering around the correct rpm. Sometimes it idles with a rhythmic faster-slower pattern and occasionally it will spike up to 1100 rpm or so. General driving performance is good, though it can hesitate slightly when pressing on the accelerator. I've had my local garage plug it into a code reader and nothing showed up. I've replaced the ISCV (45 quid, new genuine Ford part) and no improvement. I've tried disconnecting/plugging the EGR vacuum pipe with no change at all. My next step may be to shell out for a Throttle Position Sensor, but I thought I'd give the MAF a clean first as it costs nothing (unless I bugger it of course!) I'm a bit hesitant about changing the TPS as its output seems rock steady despite the erratic idle, though of course that doesn't necessarily rule it out as it could be out of tolerance. I'm open to suggestions on what to look at to get to the root of this problem, any suggestions appreciated. Morse Sorry, forgot to mention this is the UK RHD model. 1.6 Ghia petrol, regularly serviced and in otherwise excellent order. Morse > Sorry, forgot to mention this is the UK RHD model. 1.6 Ghia petrol, > regularly serviced and in otherwise excellent order. Either you have a vacuum leak, or your throttle body is dirty, or indeed the MAF is giving varying signals. The MAF is located just on top of the air box on the hose to the intake manifold. A quick check is to disconnect it and go for a drive. The MIL will be lit, but if the idle quality is better or the same (not worse) then the MAF is at fault. Check for intake leaks very carefully first though.- espcially the PCV system. I would also blank off the EGR valve for trial purposes too. Disconnecting the actuation will not stop a physically leaky valve leaking. Tim.. >> Sorry, forgot to mention this is the UK RHD model. 1.6 Ghia petrol, >> regularly serviced and in otherwise excellent order. [quoted text clipped - 6 lines] > will be lit, but if the idle quality is better or the same (not worse) > then the MAF is at fault. Tim, thanks for your reply. I'm struggling a bit here, I can't find any electrical device attached to the hose- http://i196.photobucket.com/albums/aa223/morse248RPA/engine.jpg http://i196.photobucket.com/albums/aa223/morse248RPA/airboxhose.jpg The only thing that I can see on the intake system which could be the MAF is located on the end of the bottom of the manifold before it branches out- http://i196.photobucket.com/albums/aa223/morse248RPA/Intake.jpg > Check for intake leaks very carefully first though.- espcially the PCV > system. Is that the crankcase ventilation system, the small hose which goes to the airbox? It seems secure but I'll recheck. > I would also blank off the EGR valve for trial purposes too. Disconnecting > the actuation will not stop a physically leaky valve leaking. I'm not 'absolutely' sure I know which bit is the EGR valve, my guess is this- http://i196.photobucket.com/albums/aa223/morse248RPA/closeup.jpg If I'm right, I need to remove the large pipe with the red/black connector and plug both the valve and pipe? Your help is much appreciated Tim. Morse >>> Sorry, forgot to mention this is the UK RHD model. 1.6 Ghia petrol, >>> regularly serviced and in otherwise excellent order. [quoted text clipped - 40 lines] > > Your help is much appreciated Tim. You have a MAP equiped 1.6, rather than MAF- this system works on air pressure rather than volume. You will need to remove the MAP sensor, as the small air pipe often blocks with oily crud / deposits. Do NOT use carb cleaner / air line directly into the map sensor, if its little pipe is blocked, blow across the top of it with your cleaner. There is no EGR on your car- the device you marked is the fuel pressure regulator. >>>> Sorry, forgot to mention this is the UK RHD model. 1.6 Ghia petrol, >>>> regularly serviced and in otherwise excellent order. [quoted text clipped - 46 lines] > cleaner / air line directly into the map sensor, if its little pipe is > blocked, blow across the top of it with your cleaner. Thanks Tim. Do you know where the MAP is located by any chance? > There is no EGR on your car- the device you marked is the fuel pressure > regulator. Oops! There's so many hoses and odd looking gadgets on 21st century cars! A far cry from something like a MkI or MkII Escort that's for sure! Morse >>>>> Sorry, forgot to mention this is the UK RHD model. 1.6 Ghia petrol, >>>>> regularly serviced and in otherwise excellent order. [quoted text clipped - 52 lines] > > Thanks Tim. Do you know where the MAP is located by any chance? You already pointed it out in one of the photo's-it's between number 1 and 2 intake runners. Tim.. >> Thanks Tim. Do you know where the MAP is located by any chance? > > You already pointed it out in one of the photo's-it's between number 1 and > 2 intake runners. > > Tim.. Cheers Tim, looks like an alternator off job, can I disconnect it to run tests the same as the MAF sensor? Morse >>> Thanks Tim. Do you know where the MAP is located by any chance? >> [quoted text clipped - 6 lines] > Cheers Tim, looks like an alternator off job, can I disconnect it to run > tests the same as the MAF sensor? You're looking for a PWM ~0.5 to 5v output on pin 2. I tend to use the tacho function on my DVM if I havent my scope handy. Tim.. >>>> Thanks Tim. Do you know where the MAP is located by any chance? >>> [quoted text clipped - 11 lines] > > Tim.. Thanks Tim, I'll have a look at it. Morse >>>> Thanks Tim. Do you know where the MAP is located by any chance? >>> [quoted text clipped - 11 lines] > > Tim.. Tim, I haven't got around to checking the signal from the MAP sensor, but it seems the fault has taken a new twist. While I was driving it yesterday it appeared to be picking up speed by itself and when I depressed the clutch and took my foot off the accelerator the revs sat at 3000 rpm! It did this intermittently- sometimes the idle was fine, sometimes it was at around 1000-1200 etc. I managed to drive a good mile without touching the accelerator at all! The prime candidate for this fault seems to be the IACV, but I've just changed that. It doesn't rule out the new one being a dud of course. I'm more inclined to think the IACV is being wrongly controlled due to the ECU getting duff info from somewhere (TPS, perhaps? I'll recheck it). My (layman's) theory is the TPS is dodgy and is telling the ECU that the throttle is open more than it is, causing the ECU to inject more fuel and therefore richen the mixture, initially causing lumpy idle. The ECU detects the rich mixture and opens the IACV to allow more air to attempt to weaken the mixture, causing the high idle. Does this sound feasable to you, Tim? When I parked up I thought I'd gradually depress the accelerator and see what happened. The revs didn't pick up smoothly and when it got to around 2500 (IIRC), it hit a spot where it was speeding up/slowing down rhythmically. Increasing the throttle past that point actually caused the revs to dip quite a bit, it seemed to struggle then pick up again. On the road, I've noticed that it now runs out of steam at around 4500 rpm. IOW, it's not keen to rev anymore, though it performs well up to this point. Cruising on the motorway at 70mph it seems perfectly normal, no misfiring or anything like that. I'm at a loss, do you have any suggestions based on the above info? I'd bung it in the garage but money is really tight right now and since I used to do all my maintenance myself, I'm able to change most easily accessible components. I really appreciate any help you can give. Morse >>>>> Thanks Tim. Do you know where the MAP is located by any chance? >>>> [quoted text clipped - 46 lines] > to do all my maintenance myself, I'm able to change most easily accessible > components. I really appreciate any help you can give. TPS is the usual cause of a stuck high idle, check its output.. tim.. > TPS is the usual cause of a stuck high idle, check its output.. > > tim.. Tim, I spent a while with it this afternoon. The voltage from the TPS is 0.955 at idle, close to 5V at full throttle. When the revs get to around 2200 rpm, it fails to increase with more throttle, but the voltage from the TPS increases as one would expect. Keep increasing the throttle and it reaches a point where the revs suddenly pick up and hit 3000, then all seems normal. I also noticed if you snap the throttle open quickly while idling it hesitates before it picks up. The hesitation makes a slight 'cough' and there's a very brief dieseling sound before it picks up. I'm still stumped! I couldn't get it to stick at high revs like it did the other day so I couldn't take any measurements. I might rig up a semi-permanent voltmeter in the car so I can monitor it on the road. A faff on but it might give me some insight as to what's happening. Morse |
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