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Old 07-04-2014, 10:03 PM   #41
Eno
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Originally Posted by Cosmo Dude View Post
Measure the voltage on the fuel pump with engine hot both and cold as well as below 2500rpm and above 2500rpm or when the problem strikes.
I'm not saying it is the fuel pump just using it as a point of reference.
That makes sense, I'll give that a go in the morning & report back.
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Old 10-04-2014, 01:59 PM   #42
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it could also be your circuit opening relay, its the relay that controls the fuel pump... As cosmo said measure the voltage at the fuel pump but you might need to use an analog meter to be able to see the change in voltage, as digital unit might not refresh quick enough for you too see the voltage drop.
If the relay gets hot it might disconnect, and as soon as it disconnect and no current going through it quickly cools down and connects again. So you got the cycle going of the relay going on and off.
The reason it would happen when you rev it is that as revs go up so does the fuel pressure in the lines so does the current in the fuel pump, thus putting more load on the circuit opening relay. It generally would take bit of time for the relay to get hot as well and thats why it starts doing so when things get hot.

Fault fuel pump might cause the issue as well if it stalls under certain load and generally this would happen when it gets hot.... you can check this by measuring the current through the power line going to the fuel pump. You should get a steady rise in current as you rev the engine. If you get a spike of current (up or down) as the engine oscillates that would indicate abnormal operation of the fuel pump. But again it would be best to use an analog multimeter for such measurements.
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Old 14-04-2014, 11:22 AM   #43
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I measured a constant voltage on the fuel pump from cold start onwards, plus I've replaced the fuel pump & the fuel regulator & checked the vacuum that connects to it.
There can't be much left?
When the fault occurs the engine still sounds smooth so it's not injectors or individual spark etc.
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Old 14-04-2014, 11:28 AM   #44
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Voltage may be constant but what was it?
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Old 14-04-2014, 08:07 PM   #45
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The video looks like it hunts from idle to 2500rpm and then it seams to rev normally at higher revs. To confirm it go for a drive and see if it drives normally at higher revs - idling in the yard won't tell you if it's working normally at higher revs because there is no load -. The TPS is a simple switch that activates at a certain throttle position, and if the car works normally at higher revs it indicates the switch is switching too late - TPS not adjusted -. The reason the TPS has no effect when cold is a temp switch is telling the CPU the engine is cold, and to keep the TPS rich circuit switched on until the temp switch get hot and switches to tell it to go to normal lean driver circuit.

Take the TPS off and manually turn the rotator when the engine is hunting and see if there is a position that lets the engine run normally.

Also try unplugging the temp sensor and plugging your old one in and grounding it on the body. The sensor will always be cold so it should run fine if it's controlling the circuit.

These might not be the answer but it may tell you something.

I asked you to do things to check the pump at the start of your post and you never said if you did them or if there was any result - it was a long shot IMHO, but you never know -. Now you post that it power stays on constantly when it happens so elec supply doesn't seam to be a problem but it still doesn't rule out pressure, and that means a pressure gauge.

I think the vacuum tube on the regulator tells it to lower the pressure with slow driving, and raise pressure at WOT. And that would mean that if it leaked the pressure would be high.

Last edited by Old Grey; 14-04-2014 at 08:13 PM.
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Old 15-04-2014, 08:00 AM   #46
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Voltage may be constant but what was it?
Battery voltage or close to it.
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Old 15-04-2014, 08:40 AM   #47
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The video looks like it hunts from idle to 2500rpm and then it seams to rev normally at higher revs. To confirm it go for a drive and see if it drives normally at higher revs - idling in the yard won't tell you if it's working normally at higher revs because there is no load -. The TPS is a simple switch that activates at a certain throttle position, and if the car works normally at higher revs it indicates the switch is switching too late - TPS not adjusted -. The reason the TPS has no effect when cold is a temp switch is telling the CPU the engine is cold, and to keep the TPS rich circuit switched on until the temp switch get hot and switches to tell it to go to normal lean driver circuit.

Take the TPS off and manually turn the rotator when the engine is hunting and see if there is a position that lets the engine run normally.

Also try unplugging the temp sensor and plugging your old one in and grounding it on the body. The sensor will always be cold so it should run fine if it's controlling the circuit.

These might not be the answer but it may tell you something.

I asked you to do things to check the pump at the start of your post and you never said if you did them or if there was any result - it was a long shot IMHO, but you never know -. Now you post that it power stays on constantly when it happens so elec supply doesn't seam to be a problem but it still doesn't rule out pressure, and that means a pressure gauge.

I think the vacuum tube on the regulator tells it to lower the pressure with slow driving, and raise pressure at WOT. And that would mean that if it leaked the pressure would be high.
I posted the second video because it shows the car revving normally from cold until the problem starts. The video cuts off during the interim period between being ok & not ok, & it is only for this 1 min interval that you can sometimes still plant the throttle & get it to rev higher. If the camera batteries lasted another 30 secs it would have been impossible to rev over 2400 rpm no matter what I do with the throttle. The car is not drivable what so ever, I tried once & struggled to get back & I was still in my street.

The TPS has been replaced, I also tried turning it within it's adjustment limits whilst the fault was there but the fault remained, I've traced all the signals back to the ECU & they are all ok. The TPS is very basic, it signals closed or wide open, or between open & closed, it doesn't signal an exact position between open and closed so very basic.

I have 2 resistors that i put across the temp sensor plug for forcing a hot or cold signal as per the manual, although it makes some difference it doesn't make the fault go away.

I replaced the fuel pump & fuel pressure regulator but no change, constant battery voltage to the pump as well. I pinched the return fuel line but no difference, I also removed the fuel pipe & cranked the engine & I wasn't able to stop the pressure, I know this is not a proper pressure test but it's the best I can do. I had a mechanic visit me for 10 mins & I asked him to have a quick look & he also done similar tests & said that he was happy with the pressure.

I took the vac tube off the pressure regulator & there was certainly vacuum there, plus I've felt & looked & listened & searched etc for a vac leak everywhere but it all seems fine, no hissing & no perished hoses. Again it's not a vacuum pressure test but it's the best I can do.

I've recently been going over every ECU signal, I have a few anomalies to check out but I think that the difference between the manual & what I have is down to differences of the 89 BG DOHC version but I will check.
According to the manual I am missing a distributor (Ne signal & a G signal) plus I want to double check the TPS signals because the manual shows different types & differences for manual & automatic so I want to make doubly sure I have this correct before I move on.

Someone mentioned checking the knock sensor, but the manual doesn't mention one, & I couldn't find any online info on what the resistance to ground should be, I think I've found it by touch only, between the engine & firewall, low down. Any ideas anyone?
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Old 15-04-2014, 09:55 AM   #48
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Under the stereo head unit is the engine ECU and strapped to the side of that is a relay. This relay controls the fuel pump. There are two individual windings that can turn the fuel pump on... check that no one has spliced any connections into the wiring that heads to that relay. If you find anything then carefully remove it and try again.
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Old 15-04-2014, 12:53 PM   #49
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The knock sensor looks like it's on the firewall side of the block on the Gbox end.

This is a MX5 manual, the test it is on page 306, and the position on 291.

http://www.mellens.net/mazda/Mazda-Miata-1999-2001.pdf

Does the speedo still work? Maybe there is a speed sensor in the dash powered by the cable that puts the engine into limp mode if the car moves and the speedo doesn't.


Here is another MX5

http://mx5cartalk.com/forum/viewtopic.php?f=77&t=55779

Last edited by Old Grey; 15-04-2014 at 01:53 PM.
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Old 16-04-2014, 06:06 AM   #50
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Quote:
Originally Posted by Cosmo Dude View Post
Under the stereo head unit is the engine ECU and strapped to the side of that is a relay. This relay controls the fuel pump. There are two individual windings that can turn the fuel pump on... check that no one has spliced any connections into the wiring that heads to that relay. If you find anything then carefully remove it and try again.
Relay wiring looks fine, plus when I replaced the ECU it came with the relay so I can discount the relay as well. The power on the pump is constant & the pressure would seem fine, more info on that in previous recent posts.
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Old 16-04-2014, 06:23 AM   #51
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Originally Posted by Old Grey View Post
The knock sensor looks like it's on the firewall side of the block on the Gbox end.

This is a MX5 manual, the test it is on page 306, and the position on 291.

http://www.mellens.net/mazda/Mazda-Miata-1999-2001.pdf

Does the speedo still work? Maybe there is a speed sensor in the dash powered by the cable that puts the engine into limp mode if the car moves and the speedo doesn't.


Here is another MX5

http://mx5cartalk.com/forum/viewtopic.php?f=77&t=55779
Speedo & all gauges work, but the car is doing this when parked, I can not drive it at all.
Nice manuals, thanks, if the rain holds off I'll check that resistance today.
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Old 16-04-2014, 07:19 AM   #52
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The speedo is probably just a RX7 problem.

Mine fell off just as I got home the night before and didn't notice. The next morning I had trouble getting it to run because the CPU goes into some sort of fail mode when the car moves but doesn't sense the movement. It was only after I drove back and forth in the driveway that I noticed the speedo wasn't working, and after reconnecting it and doing a few more back and forths it fixed it's self. I doubt you have the same problem but my RX7 had trouble even idling.

This is another RX7 story that you're probably not going to like. A guy I know bought an Aust RX7 without a CPU. Everyone said that it wouldn't run with an imported Jap CPU, but because he had one he plugged it in and it worked. It ran for 8 months until he hit a big bump and the car stopped. More imported CPUs would work, and it was only after he got an expensive Aust one that started running again. I have noticed problems with electrics in Mazdas, ie 323 & RX7 clocks, all ancillary circuits in the RX7 when the car is left to sit - driving seams to shake the connections and keep them clean -, so I'm wondering if the CPU has developed a fault due to moisture in the circuit board or if some connector has corrosion and not giving a signal to the CPU.

Last edited by Old Grey; 16-04-2014 at 07:33 AM.
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Old 16-04-2014, 11:51 AM   #53
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Had a little play with the knock sensor today, the sensor is in a difficult position but I tried to get as accurate results as I could.
With the cable unplugged, the sensor was a constant 870 ohms to ground when cold.
With it still unplugged the fault was slightly different, it now revs to 3000 rpm & dies back to 2750 & back to 3000 in that continuous cycle, so the fault is similar but it has definitely changed from a max of 2500 to a max of 3000.

It is important to note here that this is the first time the fault has ever changed!!!

So just to be sure I measured the sensor to ground when it was warmer, & it was a constant 14K ohms. I wasn't expecting a change, tested it a bunch of times & it was definitely 14K. I couldn't test it when it was hot as it was too hot to access the sensor without getting burnt.
I'll wait for it to cool down for a few hours & test it again.

So Old Grey posted a Mazda Miata manual that showed the resistance to ground should be 560K.

The question now is, is the Astina knock sensor different, I added a 560K resistor between ground & the knock sensor wire (sensor still unplugged). No change to the new 3000 rpm max. Dam, I was hoping that might work.

Plugged it all back together, still no change to the new 3000 rpm max.

Ummmm, not sure, I hadn't touched anything else so this could be it, just to be sure I unplugged & plugged the cable back in a few times just to be sure of a good connection but the new 3000 rpm fault remained.

Maybe the sensor is faulty & the Astina version should be something other than 560K, I think this definitely needs verifying. I've already failed to find anything online but I'll try again, anyone have any thoughts on this or could they test their own & post the resistance back for me to try.
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Old 16-04-2014, 09:59 PM   #54
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These are other MX5 manuals

http://www.mellens.net/mazda/index.html

It's a shame you don't have timing light because it would have shown that the ignition was retarded from std.

http://www.youtube.com/watch?v=0MSv6-mXhBk
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Old 19-04-2014, 07:16 AM   #55
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Unfortunately the reason I can't find any info on the knock sensor is because the car doesn't have one, I believe the sensor I unplugged must have been the oil pressure sensor which can not affect this fault, dam........what now?
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Old 19-04-2014, 06:37 PM   #56
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Unfortunately the reason I can't find any info on the knock sensor is because the car doesn't have one, I believe the sensor I unplugged must have been the oil pressure sensor which can not affect this fault, dam........what now?
I thought it was odd the the Astina has a knock sensor, and explains why it's not in the Astina manual, but just in case I posted the MX5 manual so you could check.

Can you actually drive around when it's cold, ie, will it take load, if so you might be able to disable the temp sensors and make it drivable. Maybe buy extra sensors and connect them up and just leave them in a cup of cold water while you drive around.

Also check if there are air pockets in the radiator that are lowering the water level below the level of the sensor so that it's not reading the temp properly.

Last edited by Old Grey; 19-04-2014 at 06:39 PM.
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Old 16-05-2014, 03:49 PM   #57
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I thought it was odd the the Astina has a knock sensor, and explains why it's not in the Astina manual, but just in case I posted the MX5 manual so you could check.

Can you actually drive around when it's cold, ie, will it take load, if so you might be able to disable the temp sensors and make it drivable. Maybe buy extra sensors and connect them up and just leave them in a cup of cold water while you drive around.

Also check if there are air pockets in the radiator that are lowering the water level below the level of the sensor so that it's not reading the temp properly.
The car is not driveable during the fault, it doesn't have enough revs to drive but it can crawl along very slow on flat ground.
Early tests show that the temp sensor has little affect on the fault.
I disconnected the temp sensor & added a resistor instead, the fault occurs despite sending high or low temp resistance back to the ECU.
So the fault occurs despite what the ECU thinks the temperature is.

Last edited by Eno; 22-05-2014 at 05:33 AM.
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Old 17-05-2014, 07:56 PM   #58
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i now have my hands on a BG so if you want me to test a few things to see if i can replicate the problem just let me know
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Old 22-05-2014, 05:34 AM   #59
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i now have my hands on a BG so if you want me to test a few things to see if i can replicate the problem just let me know
Thanks, I'll be in touch. Have had a few other things to do so the poor old car has taken a backseat for a while, I think I also needed the break from thinking about it.
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