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chrisnz
PostPosted: Tue Nov 21, 2017 9:23 am 
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Hi guys, over the past few weeks, I've noticed the occasional random shudder (misfire?) when idling, so I pulled my spark plugs one morning. They all looked fine, so I decided to wait until I've got a free (sunny) weekend to have a closer look.

Unfortunately, the problem got suddenly way worse a couple of days ago. Power on acceleration basically disappeared - I was struggling to get away from traffic lights a couple of times, and got some pinging, so I nursed it home and have parked up until I sort it out.

Here's a video of what's going on:
https://streamable.com/7qghw
I'd put the car in neutral (with handbrake) and half-gunned it. There's a sort of chug-chug-chug hesistant feeling as soon as I press the pedal.

What I've done so far:
1. Checked engine codes - Got #23 and #24 "Heated Oxygen Sensor RH" but this doesn't seem relevant.
2. My first thought after plugs was leads, so I measured all of the resistances - all within spec.
3. I pulled each lead in turn and looked for a drop in revs. Cylinder #5 didn't show much of a drop, so I switched out that lead with one from another car, which showed a drop, but didn't solve the main problem.
4. I took my distributor cap off and gave the contacts a quick sand with 400 grit - didn't seem to help.
5. Replaced the distributor cap with a spare - didn't help either.

My thoughts are:
- Vacuum leak?
- Fuel filter blocked?
- Mass airflow sensor?

Grateful for any help or suggestions!


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brucey76
PostPosted: Tue Nov 21, 2017 7:51 pm 
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that doesn't sound very smooth at idle. I'd check your base timing and check the belt hasn't slipped a tooth on one of the cam sprockets. The o2 sensor will have an effect on fuelling. I had a kl-de with similar symptoms and rotating the dizzy toward the front of the car stopped the pinging. Timing was a mile out when i did that but the engine ran smooth and pulled like a train. I suspected it was the ignition amplifier in the dizzy itself but I pulled the engine before knowing for sure. It ran perfect when swapped but had all KF dizzy, Maf etc when rebuilt


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jinglebells
PostPosted: Tue Nov 21, 2017 10:19 pm 
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Ignition timing and / or air leaks would be the first suspects on my 4-cyl, but I'm not too familiar with the V6.


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chrisnz
PostPosted: Wed Nov 22, 2017 10:41 am 
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Thanks guys.

Brucey, I've never removed the cambelt cover. Am I right in thinking that to check the alignment, that it hasn't slipped, I just need to remove the frontmost cover, and that it's a matter of removing three bolts:
one down the bottom of the cover, holding a bracket holding the Crank Angle sensor,
one in the middle of the cover, holding a bracket holding the dipstick pipe, and
one up the front of the cover, which doesn't seem to hold anything.

OR, do I need to do a bunch more? I've got the Haynes for the KL-ZE, and in its instructions for *removing* the cambelt, it talks about loosening water pump pulley bolts, removing drivebelts, jacking up the car, removing tensioners etc etc.
I'm hoping that just to *check the alignment*, I can get away without doing all that!!


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brucey76
PostPosted: Wed Nov 22, 2017 11:21 am 
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You shouldn't need to remove the covers completely, they should pull back just enough to see the marks on the pully however you may need to raise the engine to see better which is just loosen the engine mount nut and Jack up. Removing the covers completely are a nightmare. I don't know why they made them so awkward


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pitrack_1
PostPosted: Wed Nov 22, 2017 5:42 pm 
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Hi,

not familiar with the actual engine so can only offer some general ideas/opinions. From the video the main issue I note is when you open the throttle rather sharply from idle. This coupled with your description of loss of power and pinging whilst accelerating is usually identified to a couple of causes and those are what I'll concentrate on. In the meantime a couple of things to try:

1) External O2 sensor up the exhaust. This should independently and categorically tell you mixture rich/lean issues.
- Rich could mean a mixture issue but also an ignition issue (unburnt fuel).
- Lean would mean a mixture issue.
- OK mixture would mean an ignition issue (over advanced) or a poor fuel quality issue (low octane).

2) Try your video again but accelerate very gradually (say over 10 secs) to some higher revs. Do that a couple of times, once closing the throttle gradually and once letting it snap shut. How it reacts to that can help diagnose things.

Some issues:
A) Overly lean mixture. The O2 sensor fault could also be related or the cause of this. Issue could be caused by:
* an air leak- check intake hose connections, vacuum pipes for leaks /disconnection and intake hose for cracks, also manifold for cracks or leaky gaskets. Although a fairly major leak (after the air flow monitor) usually results in a higher idle.
* not enough fuel- poor fuel pressure regulation, faulty injectors. ?
* O2 sensor fail or disconnection (or even ECU issue)
* If it does end up valve timing that's a real worry and the cause needs to be investigated 'cos that should never change.

B) Overly advanced timing / poor ignition
* has the base idle changed (if changeable)...bolt hasn't come loose and moved has it?
* crank angle sensors have been known to play up.
* poor fuel quality (low octane). Lower octane fuel needs retarded spark timing
Sharply opening the throttle at idle allows the engine to achieve maximum compression (max time to suck a charge of air in compared to high rpm) thus giving the highest actual compression and highest resistance to spark, this relates to the next few sub-points:
* incorrect spark plug gap
* weak ignition system
* shorting at the plug boots (failed insulation)- check for corona discharge damage
* shorting in the distributor- check for evidence in the rotor cap. Contamination in the plug cap inside OR on the rotor (I speak from experience on another vehicle). Also check for cracks/breaks and good connection in all the plug boots at the cap including the HT lead.

C) Other issues
- leaded fuel. Lead fouling will cause an engine to idle but stall under acceleration. Yes I've seen this is practice. However the diagnosis is easy- coloured lead salt (usually red I think) deposits on the plugs and you said you didn't have them so this should be discounted.
- poor or missing ground strap and/or other grounding/power connections. Bad grounds can do the strangest things

Good luck!
Patrick


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chrisnz
PostPosted: Thu Nov 23, 2017 9:08 am 
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Hi guys,

brucey76: I tried to get the front ("LH") cambelt cover off but wasn't able to bend it far enough back to see the sides of the pulley. I've got a little endoscope thing at work which I'll try borrow over the weekend, to see if I do any better.
Today I was able to borrow a timing light though. I warmed up the engine, but didn't bother to disconnect any vacuum hoses as I couldn't see any vacuum hose attaching to the distributor? The idle rpm warmed up was 750 according to the dash - I don't have a tachometer to double-check.
Anyway, the little yellow mark was jumping around between 10 deg and 8 deg (left of the "T") symbol. The workshop manual says 9-11 so that's pretty close I guess?
Ahh bugger, I've just realised I didn't short the TEN-GND like the manual says. Will repeat on weekend.

pitrack_1:
1) Will try and borrow an O2 sensor from work. I'm pretty sure I can smell unburnt fuel which as you say indicates mixture/ignition problem.
2) When I gradually increased throttle, there was no hesitation. I'd only get the hesitation when I would quickly hit throttle. When I backed off the throttle suddenly, it behaved like it normally would (the needle fell normally) - I didn't notice anything out of the ordinary.

A) The error codes I was getting were pointing at the "RH" heated O2 sensor which I think is the one near the catalytic converter, as opposed to the one by the exhaust manifold. I have a spare so I'll try swap it out on the weekend.
I didn't see any obvious air leaks anywhere.

B) I use 91 octane (typical here in NZ). I checked the spark plug gaps with a feeler gauge the other day, they're all OK. I'm a little bit leery of the spark plug leads, I'm tempted to buy another set just to rule it out! I did the "spray bottle at night" thing and didn't notice anything obvious.

C) Yes I've been wondering about the grounds too - I'll have a good look at these on the weekend.


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chrisnz
PostPosted: Sun Nov 26, 2017 9:08 am 
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Hi guys, quick update:
- Repeated the timing check, it was sitting nicely on 10 deg when I had the TEN-GND in. I'm tempted to rotate the dizzy one or two degrees just to see what happens - I'm make sure I'll mark where it's at now.
- Borrowed an O2 sensor and it was reading 1.3% when I put it up close the exhaust - I have no idea what it's meant to read - does this sound right?
- I was talking to a guy at an auto shop on Friday and he said that the RH heated O2 sensor is probably just for emissions and not used as an input for changing air/fuel mixtures. If that's the case, I won't swap the sensor out.
- That reminds me, I should have mentioned I have a "HEAT" light on my dash from a misfiring misadventure a year or so ago (solved by changing spark plugs). Presumably the cat's buggered, but in NZ, our MoT doesn't test for emissions so it's never failed on account of it.
- I found this thread: viewtopic.php?f=3&t=60061, which has very similar symptoms - and have contacted him to find out if he solved it.


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brucey76
PostPosted: Sun Nov 26, 2017 11:15 am 
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"heat" light? as in engine temp? I don't think our BA's measure the cat outputs but if you suspect its blocked it will cause the cat to glow (easier to see at night). It will cause running problems. If it cant remove combusted gases it wont be able to intake fresh. The v6 standard exhaust is very restrictive anyway and a lot of improvement when enlarged pipes are used instead but if the cat is restricting more than it should the engine wont breathe properly. https://www.doityourself.com/stry/6-sym ... -converter


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pitrack_1
PostPosted: Sun Nov 26, 2017 4:27 pm 
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Hi chrisnz,

sorry but been O/S (that's overseas, not out of service ;-) ) for past week. Some items:

1) No hesitation under gradual acceleration: Aaark! I was afraid you'd say that. With an old carby, that'd be simple: the accel pump-jet in the carby would be non-functional one way or the other. With injection I think it's more obscure.

2) HEAT light??? What does it say in the manual? A few things come to mind:
- Cat heat- the cat's getting too hot if there's a temp sensor somewhere
- inlet air heating- used to ensure proper vaporisation of the fuel. Does cause a loss of air density
- loss of heater element on an O2 sensor- does you sensor(s) have multiple wires? If so, it's for a heater element to ensure it's at proper operating temp (something like 600C)
- It's an acronym for something, eg. HEAT also can stand for (non-related) High Explosive Anti Tank (as in a projectile)

3) Does the O2 sensor say 1.3% or 1.3V? An O2 sensor puts out a voltage, low (~0.1V) for lean exhaust (where the O2 level is similar to air) up to ~0.9V or more for rich mixture where the O2's been exhauseed. If you wave it around in air does it say 21% or 0? Basically if the engine's running lean the O2 level will be high (and voltage low), O2 low and V high for rich mixture.

4) Are you doing your tests at normal operating temp? The ECU will enrich the mixture whilst the engine is cold, similar to carby choke. If the engine's not heating up (e.g. failed or removed thermostat or faulty temp sensor) then the car will remain in this permanently enriched mixture- I had a car that did that.

5) If the car's newer than 1994 (I think) you may be able to read out the sensors through the diagnostic connector link. Programs such as FORScan on Android can di this I believe. You'll need the connection dongle though and perhaps a few jumper wires to connect the appropriate pins. This can give you the codes and also perhaps the data to plot up to see what may be going wrong.


Hope this helps,

Patrick


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chrisnz
PostPosted: Sun Nov 26, 2017 7:23 pm 
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Thanks pitrack!


Quote:
2) HEAT light??? What does it say in the manual? A few things come to mind:
- Cat heat- the cat's getting too hot if there's a temp sensor somewhere
- inlet air heating- used to ensure proper vaporisation of the fuel. Does cause a loss of air density
- loss of heater element on an O2 sensor- does you sensor(s) have multiple wires? If so, it's for a heater element to ensure it's at proper operating temp (something like 600C)
- It's an acronym for something, eg. HEAT also can stand for (non-related) High Explosive Anti Tank (as in a projectile)

I've done a bit of googling around "Mazda heat light dash" and it sounds cat-related. It started up last year when I kept driving around with misfires (idiot!!), I guess the unburnt fuel must have upset the cat.

Quote:
3) Does the O2 sensor say 1.3% or 1.3V? An O2 sensor puts out a voltage, low (~0.1V) for lean exhaust (where the O2 level is similar to air) up to ~0.9V or more for rich mixture where the O2's been exhauseed. If you wave it around in air does it say 21% or 0? Basically if the engine's running lean the O2 level will be high (and voltage low), O2 low and V high for rich mixture.

Oh, I see - I work for a medical company so I borrowed an oxygen sensor which reads % O2. Waving it around in air says 21%.

Quote:
4) Are you doing your tests at normal operating temp? The ECU will enrich the mixture whilst the engine is cold, similar to carby choke. If the engine's not heating up (e.g. failed or removed thermostat or faulty temp sensor) then the car will remain in this permanently enriched mixture- I had a car that did that.

The O2 one I did while the engine was still cold - I'll try again tonight once it's warm.
Car's definitely warming up OK and temp sensor appearing fine.

Quote:
5) If the car's newer than 1994 (I think) you may be able to read out the sensors through the diagnostic connector link. Programs such as FORScan on Android can di this I believe. You'll need the connection dongle though and perhaps a few jumper wires to connect the appropriate pins. This can give you the codes and also perhaps the data to plot up to see what may be going wrong.

Thanks - I think I need a special cable adapter for this, as I've got the 17-pin Mazda one. I'll see what I can do about getting one.


Cheers,

Chris.


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pitrack_1
PostPosted: Mon Nov 27, 2017 12:33 pm 
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Hi Chris,

Firstly I'd be more likely to trust a car-type O2 sensor probe! You can build/buy one from a kit from Jaycar quite cheaply.

Just had a look at the Haynes manual for my Mazda 3. Although a different vehicle, the troubleshooting should be similar as most EFI systems function use similar parts and function in a similar manner.

Engine stumbles on acceleration
1. Spark plugs fouled
2. Problem with fuel injection or engine control system
3. Fuel filter clogged
4. Intake manifold air leak
5. Problem with emissions control system

Pinging or knocking engine sounds during acceleration or uphill
1. Incorrect grade of fuel
2. Fuel injection system faulty
3. Improper or damaged spark plugs or cylinder (wrong heat range quite possible)
4. Knock sensor defective (you may not have this- not sure with your engine)
5. EGR valve not functioning
6. Vacuum leak
7. (my 2c worth- could also be carbon buildup in the cylinder causing the pinging, but this would be quite rare on a modern ECU controlled engine. )
There's a couple of overlaps, namely the leaks, EGR/emissions and fueling issues.

You can check for vacuum & manifold leaks (same thing really, just different sources) with a can of aerostart. Carby cleaner is another one you can use- just needs to be a flammable hydrocarbon source. In fact carby cleaner may be better as it's a liquid and will sit for a few seconds and work until it evaporates, confirming the diagnosis. Warm the car up to normal operating temp. If you spray the aerostart/carby cleaner near the suspect areas (vacuum connections, gaskets, joints, etc) the engine revs will increase if there's a leak. The carby cleaner will sit and raise the revs until it evaporates (although the ECU may try to compensate for this). Be careful- the stuff is highly flammable so do it in a well ventilated area and keep it away from the ignition system.

If you suspect the cat is blocked you could disconnect the exhaust before it and run the engine and see if the accel baulking issue is still there (ignore the sudden loud noise issue :-) )

You can change the fuel filter, run some strong fuel system cleaner through, use some higher octane petrol for a tank and see how they go. If it's a JDM import engine/ECU it probably requires 98 (if not higher) octane.

If you get the scanner to read out the ECU parameter, have a look at the fuel trim (if available)- both long term and short term values. High ones indicate lean running (likely air/vacuum leak or low fuel system pressure), low ones show over-rich (blocked air intake, faulty sensor, injectors, etc)

These are some of the simpler tests, unfortunately it could still be something like a (partially) faulty sensor, even your exhaust problem (Cat/O2 sensor) maybe even the cam timing being out as Brucey suggested.

Patrick


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chrisnz
PostPosted: Mon Nov 27, 2017 7:19 pm 
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Thanks Patrick, very much appreciated.
I had another go at checking the cam belt slippage last night, but even the endoscope wasn't helping me see! Also, played with the base timing between 5 and 15 but didn't notice a difference.

My plan now is to move the Lantis from being my daily driver to my project car - which means the pain of buying another car, sigh.

Once I've solved the issue I'll post back in case it helps anyone else!

Thanks again to you and brucey for your help.


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brucey76
PostPosted: Mon Nov 27, 2017 7:54 pm 
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From your other posts I'd be trying to remove the cat, if they're not compulsory over there and you find it has become blocked or partially blocked then knock a big hole through it to increase the flow or replace with a "test" pipe and see how it performs. If you've got neighbours that don't complain about noise just disconnect the cat from the downpipe and let rip, WARNING there will be a LOT of noise, I'm talking wake the dead 5 miles away noise


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