Hi all, I created an account just to try and solve this problem on my project car swap. I'd really like your thoughts on the issue, but I guess even if noone has any ideas it helps my head to write it all in one place.
I've had this issue for probably 2-3 years, and since I'm finishing up everything else and trying to get it roadworthy I really need to sort this, but I'm just struggling to work out what to do.
Basically, I have a later non-vvti 1UZ swapped into a miata. TL;DR, it runs so rich and pours smoke out of the exhaust. Long version of the problem is this:
ECU power on, key on, gives code error 31 for MAF.
Engine turned on, it starts perfectly and settles into a good idle. 14.7afr, spot on. Then... after about 5 seconds, the afr drops slowly. After about 10 seconds, the afr is on the minimum reading of 10afr, and smoke starts to come out the exhaust. The smell of fuel is horrendous. However, it runs and idles just fine. Revs up nicely. Seems to have decent power, I dont think its in limp. When codes are checked after engine on, I get the following:
21- o2 sensor (AEM output wired into ECU, 0v-1v)
27- sub o2 sensor (it doesnt have one)
28- o2 sensor (AEM output wired into ECU, 0v-1v)
29- sub o2 sensor (it doesnt have one)
31- AFM error
71- EGR (deleted, blanked)
78- fuel pump (Uses aftermarket bosch 044 wired to a panel switch)
It is running stock ECU and wiring harness it came with. Manualised auto box. Plastic maf. AEM wideband with narrowband 0-1v output into stock ecu.
Okay so lets list the diagnostics I've done so far:
Coolant temp sensor test at sensor, resistance within spec for ambient temps.
Opened ECU, checked for faulty caps. Seems fine, no evidence of leaks or damage.
I was using thin oil, swapped it for thicker stuff in case it was leaking past stem seals or something.
Wired in o2 sensors. I was originally using no o2 sensors, so wired in the AEM gauge narrowband output of 0-1v to the two main o2 sensor wires to the ECU.
Replaced MAF
Replaced MAF plug (wire was split)
Checked maf wiring. THA and E2 have correct resistance across them, 2.6kohm. E2, THA, VG all have continuity to ECU. I cant figure out what pin B and E2G connect to? I cant get continuity of B to anything. E2G has a connection to ground with negligible resistance. E2 has connection to ground with negligble resistance. THA has 5v.
When MAF is disconnected, there is no change at all.
And no, I havent put any cleaning solution through the MAF!
To me this seems to point to the MAF. The 31 code, unplugging and it does nothing... OR injectors stuck open. OR the classic faulty ECU. In that order.
So next I think to diagnose on the MAF is finding continuity between B and something. I dont have a frequency thingy in order to test the output frequency, I assume is the VG wire. I might have to invest in one. I might even buy a THIRD MAF just to make sure. But I suspect wiring is the culprit.
Lambda sensors - its just the narrowband output from AEM wideband running stright to OXL1 and OXR1 together. Voltage has been verified to be correct. Is it really as easy as this? I assume the errors are for things like the heater circuit having an open reading as the correct sensor is not present?
As for the injectors - when I disconnect one or two the smoking is reduced and the afr rises to about 10.2, but I dont really think im proving anything here because it must be all of them together to be smoking this bad. It doesnt sound like its just one cylinder, it sounds pretty smooth for its condition, no misfires. If they were stuck open, why would the car run so well in the first 5 seconds and drop down the afr range so smoothly? The same for fuel pressure. I had suspected the pump I was using was too good and is overwhelming the regulator and causing rail overpressure, but if this was the case then it would be rich right from the engine start.
Really any thoughts are appreciated. Especially on MAF and lambda sensor error fixing. I'm fairly confident the error is somewhere in the wiring. If I can get rid of these main codes I might be able to solve the issue. I've probably spent upwards of 100 hours just trying to figure out why its smoking so much. So sorry if this is a bit rambly, I think I'm losing my mind.
I've had this issue for probably 2-3 years, and since I'm finishing up everything else and trying to get it roadworthy I really need to sort this, but I'm just struggling to work out what to do.
Basically, I have a later non-vvti 1UZ swapped into a miata. TL;DR, it runs so rich and pours smoke out of the exhaust. Long version of the problem is this:
ECU power on, key on, gives code error 31 for MAF.
Engine turned on, it starts perfectly and settles into a good idle. 14.7afr, spot on. Then... after about 5 seconds, the afr drops slowly. After about 10 seconds, the afr is on the minimum reading of 10afr, and smoke starts to come out the exhaust. The smell of fuel is horrendous. However, it runs and idles just fine. Revs up nicely. Seems to have decent power, I dont think its in limp. When codes are checked after engine on, I get the following:
21- o2 sensor (AEM output wired into ECU, 0v-1v)
27- sub o2 sensor (it doesnt have one)
28- o2 sensor (AEM output wired into ECU, 0v-1v)
29- sub o2 sensor (it doesnt have one)
31- AFM error
71- EGR (deleted, blanked)
78- fuel pump (Uses aftermarket bosch 044 wired to a panel switch)
It is running stock ECU and wiring harness it came with. Manualised auto box. Plastic maf. AEM wideband with narrowband 0-1v output into stock ecu.
Okay so lets list the diagnostics I've done so far:
Coolant temp sensor test at sensor, resistance within spec for ambient temps.
Opened ECU, checked for faulty caps. Seems fine, no evidence of leaks or damage.
I was using thin oil, swapped it for thicker stuff in case it was leaking past stem seals or something.
Wired in o2 sensors. I was originally using no o2 sensors, so wired in the AEM gauge narrowband output of 0-1v to the two main o2 sensor wires to the ECU.
Replaced MAF
Replaced MAF plug (wire was split)
Checked maf wiring. THA and E2 have correct resistance across them, 2.6kohm. E2, THA, VG all have continuity to ECU. I cant figure out what pin B and E2G connect to? I cant get continuity of B to anything. E2G has a connection to ground with negligible resistance. E2 has connection to ground with negligble resistance. THA has 5v.
When MAF is disconnected, there is no change at all.
And no, I havent put any cleaning solution through the MAF!
To me this seems to point to the MAF. The 31 code, unplugging and it does nothing... OR injectors stuck open. OR the classic faulty ECU. In that order.
So next I think to diagnose on the MAF is finding continuity between B and something. I dont have a frequency thingy in order to test the output frequency, I assume is the VG wire. I might have to invest in one. I might even buy a THIRD MAF just to make sure. But I suspect wiring is the culprit.
Lambda sensors - its just the narrowband output from AEM wideband running stright to OXL1 and OXR1 together. Voltage has been verified to be correct. Is it really as easy as this? I assume the errors are for things like the heater circuit having an open reading as the correct sensor is not present?
As for the injectors - when I disconnect one or two the smoking is reduced and the afr rises to about 10.2, but I dont really think im proving anything here because it must be all of them together to be smoking this bad. It doesnt sound like its just one cylinder, it sounds pretty smooth for its condition, no misfires. If they were stuck open, why would the car run so well in the first 5 seconds and drop down the afr range so smoothly? The same for fuel pressure. I had suspected the pump I was using was too good and is overwhelming the regulator and causing rail overpressure, but if this was the case then it would be rich right from the engine start.
Really any thoughts are appreciated. Especially on MAF and lambda sensor error fixing. I'm fairly confident the error is somewhere in the wiring. If I can get rid of these main codes I might be able to solve the issue. I've probably spent upwards of 100 hours just trying to figure out why its smoking so much. So sorry if this is a bit rambly, I think I'm losing my mind.