Astina 89 BG Sensors

Eno · 26-07-2013, 09:47 AM

My sons 1989 Mazda Astina BG has a problem, which means I have a problem. It starts and idles fine but if you increase the revs it gets to 2500 RPM & then dies & then back to 2500 & repeats this up & down cycle. It starts fine & revs normal on a cold morning, but after 1 minute the fault returns for the rest of the day. I have tested many things including TPS & MAF but I'm open to any suggestions, it's my sons & he can't just buy parts on a hunch, he needs to prove a part is faulty but I've wasted too much time on it so please please HELP!! I've also disconnected the o2 sensor on the manifold & there is no change plus all the air & vacuum pipes look ok.
I can easily take voltage & resistance measurements if someone knows what to check.
It is interesting that it is ok for a minute only if it is cold (overnight cold), but after warming up for only a minute the fault returns, that has to point to something for those that know more than me.
Here is a link to a quick video: http://youtu.be/a8D3IpVmIPk

rodhog · 27-07-2013, 01:17 AM

sounds like if it's only warm the Engine temp sensor. Because if memory serves me correct stack TB runs coolant through the Air by pass valve, so they are working against each other. I had a similar problem but I changed the air-bypass valve. But only after I did check the output of the temp sensor. But Not sure if it was on the same car.

02 sensors is only for highway closed loop.

when it warms up disconnect the Air-bypass unit on the throttle body and see if it stops.

You can then if from both cold and hot check the output of the engine temps sensor. should be a noticeable difference about 1Kohm on cold to 200or 300 ohms when hot.

and continuity on the air bypass solenoid. about 6 ohms or so.

Eno · 27-07-2013, 08:39 AM

Thanks Rodhog, there are some small differences but the fault is still there if I pull the cable on the TPS or the air bypass valve.
The air bypass solenoid has 3 pins, on the cable end I measured 8v, GND, 10v. I don't know if this is correct.
Across the solenoid is 12 ohms.
I removed the air bypass solenoid assembly & the shaft inside turns freely, I also applied 12v & can get the solenoid to move in both directions although I only heard this I could not see it so apart from the incoming voltage I think this is ok.

I can only find one temp sensor, it is definitely not working & has not been for a few years, if I pull the single wire there is no difference apart from the fan stops. I know the fan should not be on until it gets very hot but it is on continuously because of this temp sensor. It has been like this for many years so I'm assuming it is not that, is there another temp sensor as I suspect this is only for the fan. If I pull this temp sensor wire the dash temp gauge continues to work & show normal temps, where does that signal come from & is it the same signal as the ECU uses?

I have some good pics to show where the temp sensor I'm checking is (beneath the distributor & towards the TB) along with photos of inside the VAF & TPS which may be good info for the forum especially the VAF as it is normally sealed but I'm not able to upload images/attachments, maybe because I'm a newbie. Any help there would be good.

One last thing, I looked at the TPS & it is just 2 switches, one for idle & one for fully open, I'm no mechanic but that doesn't really show the position of the throttle, am I missing something here? It's part of the TB & directly connected to the butterfly valve.

BrownDog · 31-07-2013, 07:30 AM

Try resetting the ECU by disconnecting the battery and holding ur foot on the brake for about a minute

Eno · 31-07-2013, 09:38 AM

Thanks BrownDog
I've tried resetting the ECU but unfortunately it didn't fix the fault. But the problem seems so similar to yours that I'm suspecting it is the voltage on the cable going to the TPS that is the problem. I only suspect this because 7v & 10v seems a strange voltage to have (see earlier posts), can anyone verify what the voltage should be. If anyone has a BG could they start the vehicle & pull the TPS cable & measure the voltage on the cable, it is 3 pins with the middle pin being ground.
I don't even know where this voltage comes from but presumably it goes to the ECU, maybe it comes from the ECU as well. I'm going to try & hunt this down with google along with tracing the wires.
I will definitely report back here if I fix it so please don't think no news is good news.
Any & all help is much appreciated.

rodhog · 31-07-2013, 10:05 PM

TPS is **** on early BP's only the 626 of that era and Rx-7 and 929 had a full TPS.

the one you pulled is fan switch. But you must have a engine temp sensor for cold start.
it will have two pins. usually in the head. I can't remember where. someone might have photo I thought it was behind or near the distributor on BP. Mind you this is BP DOHC ? or SOHC or is it a 1.5L

Eno · 05-08-2013, 03:28 PM

Thanks RodHog
I found the temp sensor for the ECU, removed it & gave it a proper test & it is working exactly to the spec. It wasn't difficult to find, it was exactly where it should be, haha. Under the distributor & slightly towards the firewall, it is 2 pins with a green plug, it was just hidden behind a bunch of cables.
I also removed the air bypass solenoid (again), but this time I tested it in such a way that I could see the solenoid turn & allow more air in when the ignition was on & return to allow less air when the ignition was off.
So I've ruled out all the obvious stuff, TPS, air bypass solenoid, MAF, TB, vac pipes, temp sensors, both engine earths & an ECU reset.
But the fault still seems to be temperature related, & just lately it got very cold & the car spluttered & barely kept going on idle & using the accelerator just made it worse. A normal morning & it would be fine for about 1 minute & then not able to accelerate past 2500 revs before it dies & then comes back to 2500 before dying again & would stay that way until the next morning.
I have 4 things that i would still like to try which are:
1/ I'm still not sure that there should be 8v, GND, 10v on the air bypass solenoid cable, so far I've not found any info on this, see earlier posts.
2/ Check the connections to the ECU.
3/ Check the continuity of all the previous mentioned sensors back to the ECU.
4/ Check the ECU itself for any obvious visual problems such as blown components or bulging capacitors etc.

It could so easily be one of these 4 things above but I feel like I'm now clutching at straws so I'm still after as much help as I can get.

Eno · 07-01-2014, 11:56 AM

I've been a bit busy & haven't had time to spend on this, the car has just sat there in all that time but my son now needs it to get to Uni so it's time I fixed it.
I've taken the ECU out & gave it a visual inside, it looks brand new so the seals were good & no obvious component problems such as bulging capacitors etc. I've also visually checked the ECU connections & they also seem fine.
Does anyone have any other ideas, so far the fault has not changed despite all the tinkering so is there something that I have forgotten to check.
Any & all help appreciated on this, thanks.

rodhog · 08-01-2014, 12:48 AM

With out having a good think about it again. Have you changed the fuel filter? only going off your first post way back. Sounds weird but just a thought when I think about it from a cold and hot and injector band width and Pressure regulator as it revs. Doesn't make sense at first but sometimes it's best to go back to basics.

Eno · 08-01-2014, 08:48 AM

Hi Rodhog I was going to do the fuel filter & then I dismissed it for some reason, maybe it was because I can rev the nuts off it when it's cold but presumably that could be using the fuel that's in the line etc.
I'll get that filter changed today hopefully & report back.
Thanks.

Eno · 08-01-2014, 04:07 PM

Ok, fuel filter changed but no difference, the fuel was clean with no hint of debris or gunge etc. The old filter was not blocked, I could blow through it very easily.
I also took the plugs out again & 3 were oily & 1 was slightly drier with more of a carbon build up, I'm sure they were new about a year ago but they have only done about 100KM.
Anyway I gave them a clean & put them back in.
If the weather is ok tomorrow I will try & trace the temp sensor back to the ECU just to make sure the ECU gets the correct reading as I know the sensor is ok.

Where should I go from here?

Eno · 09-01-2014, 04:50 PM

I made up a diagnostic LED thingy & connected it up to read the error codes, but unfortunately there were no codes. I pulled the air intake cable & at least it showed a fault code then so it did work correctly.
Dissapointing but at least it's another thing ticked off, I'm assuming i don't need to trace the sensor signals back to the ECU now, because there are no error codes the sensor signals should be ok.
FYI, I looked for error codes when it was cold & hot, which equates to checking when the fault is not there & when the fault returns when it heats up.

Please help.

26-07-2013, 09:47 AM	#1
Eno Junior Member Join Date: Jul 2013 Location: Auckland New Zealand Car: Mazda Tribute & 1989 Astina Posts: 37	Astina 89 BG Sensors My sons 1989 Mazda Astina BG has a problem, which means I have a problem. It starts and idles fine but if you increase the revs it gets to 2500 RPM & then dies & then back to 2500 & repeats this up & down cycle. It starts fine & revs normal on a cold morning, but after 1 minute the fault returns for the rest of the day. I have tested many things including TPS & MAF but I'm open to any suggestions, it's my sons & he can't just buy parts on a hunch, he needs to prove a part is faulty but I've wasted too much time on it so please please HELP!! I've also disconnected the o2 sensor on the manifold & there is no change plus all the air & vacuum pipes look ok. I can easily take voltage & resistance measurements if someone knows what to check. It is interesting that it is ok for a minute only if it is cold (overnight cold), but after warming up for only a minute the fault returns, that has to point to something for those that know more than me. Here is a link to a quick video: http://youtu.be/a8D3IpVmIPk

31-07-2013, 07:30 AM	#4
BrownDog Senior Member Join Date: Jan 2012 Location: Beachmere Car: 1997 BA "The Red Baron" Posts: 704	Try resetting the ECU by disconnecting the battery and holding ur foot on the brake for about a minute __________________ The Red Baron Roses are Red Violets are Blue My Madza 323 Goes... SSSSSSSSTUUTUUTUU

27-07-2013, 01:17 AM	#2
rodhog Senior Member Join Date: May 2005 Location: Sydney Lakemba Car: mx-6 626 Gs300 Maz2 was 95 KF BA-HT Posts: 2,024 View Photos By: rodhog	sounds like if it's only warm the Engine temp sensor. Because if memory serves me correct stack TB runs coolant through the Air by pass valve, so they are working against each other. I had a similar problem but I changed the air-bypass valve. But only after I did check the output of the temp sensor. But Not sure if it was on the same car. 02 sensors is only for highway closed loop. when it warms up disconnect the Air-bypass unit on the throttle body and see if it stops. You can then if from both cold and hot check the output of the engine temps sensor. should be a noticeable difference about 1Kohm on cold to 200or 300 ohms when hot. and continuity on the air bypass solenoid. about 6 ohms or so.

27-07-2013, 08:39 AM	#3
Eno Junior Member Join Date: Jul 2013 Location: Auckland New Zealand Car: Mazda Tribute & 1989 Astina Posts: 37	Thanks Rodhog, there are some small differences but the fault is still there if I pull the cable on the TPS or the air bypass valve. The air bypass solenoid has 3 pins, on the cable end I measured 8v, GND, 10v. I don't know if this is correct. Across the solenoid is 12 ohms. I removed the air bypass solenoid assembly & the shaft inside turns freely, I also applied 12v & can get the solenoid to move in both directions although I only heard this I could not see it so apart from the incoming voltage I think this is ok. I can only find one temp sensor, it is definitely not working & has not been for a few years, if I pull the single wire there is no difference apart from the fan stops. I know the fan should not be on until it gets very hot but it is on continuously because of this temp sensor. It has been like this for many years so I'm assuming it is not that, is there another temp sensor as I suspect this is only for the fan. If I pull this temp sensor wire the dash temp gauge continues to work & show normal temps, where does that signal come from & is it the same signal as the ECU uses? I have some good pics to show where the temp sensor I'm checking is (beneath the distributor & towards the TB) along with photos of inside the VAF & TPS which may be good info for the forum especially the VAF as it is normally sealed but I'm not able to upload images/attachments, maybe because I'm a newbie. Any help there would be good. One last thing, I looked at the TPS & it is just 2 switches, one for idle & one for fully open, I'm no mechanic but that doesn't really show the position of the throttle, am I missing something here? It's part of the TB & directly connected to the butterfly valve.

31-07-2013, 09:38 AM	#5
Eno Junior Member Join Date: Jul 2013 Location: Auckland New Zealand Car: Mazda Tribute & 1989 Astina Posts: 37	Thanks BrownDog I've tried resetting the ECU but unfortunately it didn't fix the fault. But the problem seems so similar to yours that I'm suspecting it is the voltage on the cable going to the TPS that is the problem. I only suspect this because 7v & 10v seems a strange voltage to have (see earlier posts), can anyone verify what the voltage should be. If anyone has a BG could they start the vehicle & pull the TPS cable & measure the voltage on the cable, it is 3 pins with the middle pin being ground. I don't even know where this voltage comes from but presumably it goes to the ECU, maybe it comes from the ECU as well. I'm going to try & hunt this down with google along with tracing the wires. I will definitely report back here if I fix it so please don't think no news is good news. Any & all help is much appreciated.

31-07-2013, 10:05 PM	#6
rodhog Senior Member Join Date: May 2005 Location: Sydney Lakemba Car: mx-6 626 Gs300 Maz2 was 95 KF BA-HT Posts: 2,024 View Photos By: rodhog	TPS is **** on early BP's only the 626 of that era and Rx-7 and 929 had a full TPS. the one you pulled is fan switch. But you must have a engine temp sensor for cold start. it will have two pins. usually in the head. I can't remember where. someone might have photo I thought it was behind or near the distributor on BP. Mind you this is BP DOHC ? or SOHC or is it a 1.5L

05-08-2013, 03:28 PM	#7
Eno Junior Member Join Date: Jul 2013 Location: Auckland New Zealand Car: Mazda Tribute & 1989 Astina Posts: 37	Thanks RodHog I found the temp sensor for the ECU, removed it & gave it a proper test & it is working exactly to the spec. It wasn't difficult to find, it was exactly where it should be, haha. Under the distributor & slightly towards the firewall, it is 2 pins with a green plug, it was just hidden behind a bunch of cables. I also removed the air bypass solenoid (again), but this time I tested it in such a way that I could see the solenoid turn & allow more air in when the ignition was on & return to allow less air when the ignition was off. So I've ruled out all the obvious stuff, TPS, air bypass solenoid, MAF, TB, vac pipes, temp sensors, both engine earths & an ECU reset. But the fault still seems to be temperature related, & just lately it got very cold & the car spluttered & barely kept going on idle & using the accelerator just made it worse. A normal morning & it would be fine for about 1 minute & then not able to accelerate past 2500 revs before it dies & then comes back to 2500 before dying again & would stay that way until the next morning. I have 4 things that i would still like to try which are: 1/ I'm still not sure that there should be 8v, GND, 10v on the air bypass solenoid cable, so far I've not found any info on this, see earlier posts. 2/ Check the connections to the ECU. 3/ Check the continuity of all the previous mentioned sensors back to the ECU. 4/ Check the ECU itself for any obvious visual problems such as blown components or bulging capacitors etc. It could so easily be one of these 4 things above but I feel like I'm now clutching at straws so I'm still after as much help as I can get.

07-01-2014, 11:56 AM	#8
Eno Junior Member Join Date: Jul 2013 Location: Auckland New Zealand Car: Mazda Tribute & 1989 Astina Posts: 37	I've been a bit busy & haven't had time to spend on this, the car has just sat there in all that time but my son now needs it to get to Uni so it's time I fixed it. I've taken the ECU out & gave it a visual inside, it looks brand new so the seals were good & no obvious component problems such as bulging capacitors etc. I've also visually checked the ECU connections & they also seem fine. Does anyone have any other ideas, so far the fault has not changed despite all the tinkering so is there something that I have forgotten to check. Any & all help appreciated on this, thanks.

08-01-2014, 12:48 AM	#9
rodhog Senior Member Join Date: May 2005 Location: Sydney Lakemba Car: mx-6 626 Gs300 Maz2 was 95 KF BA-HT Posts: 2,024 View Photos By: rodhog	With out having a good think about it again. Have you changed the fuel filter? only going off your first post way back. Sounds weird but just a thought when I think about it from a cold and hot and injector band width and Pressure regulator as it revs. Doesn't make sense at first but sometimes it's best to go back to basics.

08-01-2014, 08:48 AM	#10
Eno Junior Member Join Date: Jul 2013 Location: Auckland New Zealand Car: Mazda Tribute & 1989 Astina Posts: 37	Hi Rodhog I was going to do the fuel filter & then I dismissed it for some reason, maybe it was because I can rev the nuts off it when it's cold but presumably that could be using the fuel that's in the line etc. I'll get that filter changed today hopefully & report back. Thanks.

08-01-2014, 04:07 PM	#11
Eno Junior Member Join Date: Jul 2013 Location: Auckland New Zealand Car: Mazda Tribute & 1989 Astina Posts: 37	Ok, fuel filter changed but no difference, the fuel was clean with no hint of debris or gunge etc. The old filter was not blocked, I could blow through it very easily. I also took the plugs out again & 3 were oily & 1 was slightly drier with more of a carbon build up, I'm sure they were new about a year ago but they have only done about 100KM. Anyway I gave them a clean & put them back in. If the weather is ok tomorrow I will try & trace the temp sensor back to the ECU just to make sure the ECU gets the correct reading as I know the sensor is ok. Where should I go from here?

09-01-2014, 04:50 PM	#12
Eno Junior Member Join Date: Jul 2013 Location: Auckland New Zealand Car: Mazda Tribute & 1989 Astina Posts: 37	I made up a diagnostic LED thingy & connected it up to read the error codes, but unfortunately there were no codes. I pulled the air intake cable & at least it showed a fault code then so it did work correctly. Dissapointing but at least it's another thing ticked off, I'm assuming i don't need to trace the sensor signals back to the ECU now, because there are no error codes the sensor signals should be ok. FYI, I looked for error codes when it was cold & hot, which equates to checking when the fault is not there & when the fault returns when it heats up. Please help.