Author Topic: IAT wiring Non starter  (Read 614 times)

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Offline MazdaD

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IAT wiring Non starter
« on: November 05, 2017, 10:48:26 PM »
Another issue now with my car.
Diesel, Y6 engine.
It started to have trouble starting intermittently. The starter turns over, but it won't catch or does after many attempts. Also, while cold ,it may stall.
I can start it with contsct cleaner spray in the turbo and runs alright once warm, which doesnt take long.
Disconnecting MAF wouldnt make a difference.
I checked for codes - 2 relating to IAT/ MAF

Testing the sensors, it seems they work. I also cleaned them.

So I turned my attention to the wiring of the MAF or rather, the IAT.
The black ground wire doesnt always have continuity with ground. It comes and goes.
The other wire keeps at 3 V but also ,it disapears at times.
There is no short between the wires or ground or power that I can identify.

However, if it was simply an intermittent open ground cable, it shouldn't matter because the car starts with the sensor disconnected anyway.
So I assume thst it must be a short in the cables, even though I can't see it when meassurig.
 
I would wiggle the cables and the car may start. Or not.
I traced the cables and realised that from sensor to plug in the fuse box, the cables are sound.
However ,from that plug the ground falters.
I opened the PMC harness but haven't unplugged it yet because of time and that security bolt.

The idea is to check if corrosion on the computer connecters 231 , 229 may cause this faltering and probably short  somewhere. If nothing is obvious, I intend on pulling out the IAT wires from the PCM connector and try staring the car that way. Then I'll replace whichever wire is at failt, though, tbh have no idea how to source such wires.

I wonder if anyone has had similar problems or a sparky on here may have suggestions.
Many thanks in advance!

Offline MazdaD

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Re: IAT wiring Non starter
« Reply #1 on: November 06, 2017, 10:21:40 PM »
I got the computer out, disconnected the plugs and looks like a bit of liquid on the cables. I am going to try to open the plugs a bit and wipe the liquid. It's not water , nor oil ,but it may be antifreeze following some work on the car previously.
IN
n my view, the location of the ECU is ridiculous! Low under the headlight. Easiest to get flooded , crashed or any spillage form top to go down there. It should have been way higher up in engine bay, though it may be that it would become a lot hotter there, hence the location at the bottom.

Offline MazdaD

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Re: IAT wiring Non starte
« Reply #2 on: November 08, 2017, 08:12:55 PM »
Ok, another update.
 I got to the PCM , wires all continuous from sensor to PCM connector. I took several wires out to wipe  them . liquid residue on them isn't a coolant. It can't be, as there is a curve on the wire loom upwards, so luquid wouldnt go there. Mistery what that was?!?
However, I wasnt able to trace ground on the PcM pins.
Nevertheless, put things back together, started the car, no start. Engine shakes and no start.
Unplugged MAF, and it started straightaway.
Another code thrown in, P0118, temperature sensor. Coil indicator stays on ages, fan working n full blast like an airplane turbine.
But I started the car several times, no issues.
Tried to start again after few hours, no luck.
 
Next day, scanned with EML, -40C coolant Temp. So sensor issues.
After fiddlng with wires, checking voltage, continuity, sensor resistance,, .. not conclusive other than no ground , yet ground shows voltage at times, that is, probably some short to power... I did something that I never read about anywhere and was slighly apprehensive to do it, but quite fed up after all.

Plugged a pin on the ground wire on the ECT sensor, grounded it to body and the car startd right away. Temp on scan, showing as on the dash board, fan working normally. So now it starts only when I introduced a ground to the cable on the sensor.
I wondered previously why don't sensors use ground from body, insteado f as it is now, fromPMC?
It would save tons of wires and complications.
Is there a reason for that?

If I'm correct, some older cars have sensors with one wire only, taking the ground from harness.
Would it be a problem if I disconnect ground cable at PMC and ground the sensor locally?

Many thanks.

Offline MazdaD

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Can you ground sensors at body , not computer?
« Reply #3 on: November 08, 2017, 08:21:27 PM »
My predicament is posted elsewhere. The following relates to electric query only.

Code P0118, temperature sensor. -40C coolant Temp. So sensor issues.
After fiddlng with wires, checking voltage, continuity, sensor resistance,, .. not conclusive other than no ground , yet ground shows voltage at times, that is, probably some short to power... I did something that I never read about anywhere and was slighly apprehensive to do it, but quite fed up after all.

Plugged a pin on the ground wire on the ECT sensor, grounded it to body and the car started right away. Temp on scan, showing as on the dash board, fan working normally. So now it starts only when I introduced a ground to the cable on the sensor.
I wonder why don't sensors use ground from body, instead of f as it is now, fromPMC?
It would save tons of wires and complications.
Is there a reason for that?

If I'm correct, some older cars have sensors with one wire only, taking the ground from harness.
Would it be a problem if I disconnect ground cable at PMC and ground the sensor locally?

Many thanks.

Offline Willpower

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Re: Can you ground sensors at body , not computer?
« Reply #4 on: November 09, 2017, 12:29:24 AM »
A bit out of my depth here, but perhaps the grounding system has something to do with keeping the ECU informed?


Can you keep all your findings regarding this issue in one place please, it makes it easier to follow for those like myself who are electrically challenged.   

I have merged the topics.     Thanks  :)
 
« Last Edit: November 09, 2017, 12:31:45 AM by Willpower »
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Offline MazdaD

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Re: IAT wiring Non starter
« Reply #5 on: November 09, 2017, 02:27:31 AM »
Thank you for your reply, Will.
I asked in the electrical section in case someone is of the view that my question shouldn't be here, but as you wish.

I suppose the ground from ECU is so it's refined, secure, controlled. While if it's from the harness, it may be affected by corrosion, bad contact... don't know.
As with everything in life, over regulation and control isn't that good though.

Offline MazdaD

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Re: IAT wiring Non starter
« Reply #6 on: November 09, 2017, 02:50:40 AM »
I found something:

https://blog.turbosource.com/2017/02/01/ecu-grounding-do-s-dont-s-by-adaptronic/

"This second example is one that I used to use when I interviewed support engineers to work for us, but I guess now I’ll have to think of another question to evaluate people. It’s actually a mistake made by Mazda in the factory NA6 MX5 / Miata loom; they fixed it on the next model (the NA8). The sensor ground is externally grounded to the engine, as well as to the ECU. The ECU is grounded to the engine also. We know that as the injector duty cycle increases, the average ground current of the ECU will also increase, and therefore so will the voltage drop between the ECU and the engine. The ECU ground will be sitting at a slightly higher voltage than the engine ground, so any sensors connected to the engine ground instead of to sensor ground on the ECU, will read a lower voltage. In the case of coolant temperature, it means that as injector duty cycle increases, the voltage seen by the ECU on the coolant temperature input reduces and the ECU believes the engine is at a higher temperture. This is fairly easy to spot in logs; you can look for noise on inputs such as coolant temperature, throttle position etc, but it causes problems for obvious reasons.
......
Sensors, if they have the ground isolated from the sensor body (for example TPS, pressure, temperature sensors), they must be grounded to the sensor ground on the ECU, not the engine ground. The reason for this is as given in the second example above; if you ground the sensor to the engine ground, then its output is going to be offset by the ground current times the ground resistance. This is why ECUs have dedicated sensor ground wires.
If the sensor’s ground is not isolated from the body of the sensor and it has to screw onto the engine, for example many Nissan cam angle sensors, narrowband oxygen sensors and many knock sensors, then you don’t have a choice; you have to choose the star point ground at the engine. Because the engine is so thick and low resistance, the actual point on the engine doesn’t matter too much; but often this point is on the inlet manifold or cylinder head on production cars."

Offline Willpower

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Re: IAT wiring Non starter
« Reply #7 on: November 09, 2017, 09:18:13 AM »
I'm having trouble interpreting this.  (Unsurprising for me really  :)  )  But does this mean that there is a fault in the harness, or is the ECU grounding at fault ?  or is it both ?   

 
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Offline MazdaD

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Re: IAT wiring Non starter
« Reply #8 on: November 09, 2017, 04:54:04 PM »
When I got the PCM out checking for IAT , The wires were sound but I couldn't find ground coming from the computer.I say  I couldn't , it may be there, but I suppose I know about car electrics less than you, Will.
Re temp sensor, i havent looked at the Pcm yet. Only the harness on the sensor and connector, they seem alright, so hopefully the problem is in the loom and easy to trace.
However, I was minded to just ground it at the engine instead , if PCM doesn't have ground, i,e if the computer is faulty but somehow, only this is the fault.
I have to do more investigation. It's easy for my head to start swinging when I do this kind of work ,going in circles checking for voltage, resistance, ignition on, ignition off, to and fro...

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Re: IAT wiring Non starter
« Reply #9 on: November 12, 2017, 12:41:25 PM »
I removed PCM again. Checked all grounds on the computer, there are 3 main pins for ground and quite a few output grounds for various sensors. They all have continuity between them, with the exception of the ground for MAF/IAT and the one for ECT (Engine coolant sensor). Curiously thoughm these last 2 have continuity between them only.
I put a paper clip shorting one ground from the others with the ground for ECT. This also gave ground to the IAT.
The glow plug light came off, Forscan showing proper temperstute, i.e. No -40C as before. However, the PMC gave error, the car won't start. I thought the reason was thst one of the connectors on the PCM was lose  ( work in progress onthe connector) and I pushed it in after the I had connected the battery and presumably this gave the error. However. As I freaked out that I damaged the PCm, took out the short between the grounds and simply shorted the ground at the ECT with the battery negative terminal.

The car started ok,  some wild idling,  but revving up then engine cleared the idle. I left it to idle for 30min to relearn the cycle. Started many times ok, so all good.
Next morning, no start. I used electric contact cleaner spray in the turbo to start the car. Runs fine afterwards and even though I left it for a few hours , it started straight back with no hesitation.
This morning, no start.

It may be thst the glow plugs are the he problem again. But as they were changed in August, could it be the glow plug relay, or some wiring issue?
No TDC thrown for glow plugs, but there were none either when the glow plugs were gone in the summer.

Any help would be appreciated.

Offline hanix

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Re: IAT wiring Non starter
« Reply #10 on: November 12, 2017, 03:44:21 PM »
The only modern diesels that I use are on earthmoving equipment; but what you describe (Equivalent to easystart in the intake).sounds like a glowplug problem. Check that the plugs are receiving power at start cycle i.e. amps as well as volts,if so then out with the plugs and test them.

Offline MazdaD

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Re: IAT wiring Non starter
« Reply #11 on: November 12, 2017, 05:17:13 PM »
Thank you , hanix.
I had the same problem while on holiday in Switzerland in the summer.
3 out of the 4 glows were not working at full intensity. They were changed and the car was fine right up untill recently, when it gave me TDC for IAT and MAF. It turned out these don't have a ground from PCM.
I didn't have time today'but Ill check the glow plugs this week. I even bought a clamp meter to check for intensity only to realise that it's only for AC, not DC. I suppose it's safe to disconnect the lead to the glow plug and test with multimeter. The garage in Switzerland told me that it should be circa 15A. Other than that, it may be the relay or harness???
I'd have thought that if the glow plug relay was at fault, there'd be a code thrown in.

Cheers!

Offline hanix

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Re: IAT wiring Non starter
« Reply #12 on: November 13, 2017, 07:17:23 AM »
Just a quickie. Don't overdo the squirt of primer, it can cause pre-ignition and piston damage, If all else fails it might be worth checking your compressions, although if the engine is o.k. when it is going I should think they would be sound.

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Re: IAT wiring Non starter
« Reply #13 on: November 14, 2017, 10:26:52 PM »
Thanks again.
It is electrical. It starts at times and it doesn't other time.
ECT works and shows temp when I ground it.
No ground and reading is -40C and fan turns on at full blast and remains on for several minutes ater key off. Typical for faulty ECT cuircut.
There is no ground at PCM.

The million dollar question is if PCM has to have a ground at all times or if a relay switches the ground when requred, but that relay is faulty? Or is it that PCM is faulty, in which case I can simply ground the ECT and IAT to body and drive like that?

I started to take the loom appart, but it is so  nicely done that I think not to bother. There is nothing wrong with the ECT cables, other than not having a ground from the PCM. The ground for ECT and the ground for IAT/MAF are interconnected, but not connnected to other sensor' grounds and those 3 grounds at ECM.

I gather that in some cars ECT is grounded at the body, at others - MAF and other sensors can have separate ground not at PCM, but what is it on my Mazda?
To ask Mazda Motors would be a long process (know from past experience). They even now say on their  website for technical enquiries to ask the local Mazda garage.

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Re: IAT wiring Non starter
« Reply #14 on: November 15, 2017, 11:50:45 PM »
The end of story is that PCM has no ground on those 2 sensors. So far, only this is the problem woth PCM and I won't change it. I grounded the ECT at body but may do so at another port st PCM and the car starts and drive very well.
 For good measure, I changed the ECT today, even though the old one is working fine.

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Re: IAT wiring Non starter
« Reply #14 on: November 15, 2017, 11:50:45 PM »