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Honda CRX map sensor issues

  • Crombie
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22 Sep 2019 17:28 #33780 by Crombie
Honda CRX map sensor issues was created by Crombie
After doing the engine conversion, it always seemed like it wasn't running right. I thought of the map sensor and realized its the only sensor that hadn't been changed over the years. So I installed a new one of an aftermarket brand. Immediately I noticed a difference, smooth idle, and more power through the rev range, that continued to correct the tables on the PCM. Now 5 days later, its running lumpy again and back to square one. I know this is in open loop too, so its nothing to do with O2 sensors. Though I have limited data as its OBD0, I have checked the MAP sensor wiring and probed when running in the past. I will have to look closer at the pin fitment.

I just don't understand it was like a Eureka moment of my word its fixed! Now its not after 5-6 days

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  • Cheryl
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22 Sep 2019 19:19 #33786 by Cheryl
Replied by Cheryl on topic Honda CRX map sensor issues
What is the map sensor voltage? Should be about 1 volt at idle. Coolant temp reading when it runs bad? Variable valve solenoid sticking??

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  • Crombie
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23 Sep 2019 16:56 #33813 by Crombie
Replied by Crombie on topic Honda CRX map sensor issues
Thanks, I have checked the signal to the map sensor awhile ago, but I will again at Idle cheers for that. I've also checked the signal wire to the Coolant sensor and it decreases as it warms up. It seems like its a proper misfire now at idle, since I have no catylitic convertor I will unclip the injectors and do a cylinder drop test, I've got like 4 ignition coils also, thats a parts swap, but I have them at hand and takes 10 minutes.
I don't think the vtec solenoids sticking as it engages and disengages at the right RPM, and activation settings, like having to be warmed up, over 20mph, and oil pressure, thanks for the help

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  • Crombie
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24 Sep 2019 15:39 #33842 by Crombie
Replied by Crombie on topic Honda CRX map sensor issues
I installed an old genuine Ignition coil to no effect. Installed new spark plugs no change. I disconnected each injector one by one, cylinder 3 seemed like it had the least effect, but they all created more of a misfire. The cars not overheating, I was going to do a ScannerDanner distributor cylinder drop test but even with a test light I don't like the idea of getting zapped, and the leads are a pain to put back on mine, I might just undo them at the spark plug and shut car off quick each time. Its really fuelly at idle now, and fuel vaper, so makes me think ignition related, but Im getting a fueling code 44, the 2 primary oxygen sensors are new, but I can smell a leak near the tank, I wonder if thats the code. The car didn't vape out fuel like that until about 4 days after installing the map sensor, but as I said before it totally transformed the car to perfect running and power, now its go no go in it at all, The idles at 750rpm smooth enough, then drops to 500rpm and misfires, but not all the time, but still lacks power whether smooth or misfiring

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  • Crombie
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26 Sep 2019 10:39 #33883 by Crombie
Replied by Crombie on topic Honda CRX map sensor issues
Map sensor signal 1v at idle, 0.2 ground, 4.8v power feed, coolant sensor 0.65v after a long drive. Will check valve lash next, and swap out a spare ignitor in the distributor, its a new distributor but had to grind it to get base timing set. The map sensor was perfect when i put new one on but only lasted 5 days like that, but looks like the numbers are ok

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  • Crombie
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26 Sep 2019 14:43 #33884 by Crombie
Replied by Crombie on topic Honda CRX map sensor issues
Im going to check Ignition timing again tomorrow, Im thinking maybe the trouble with the ignition timing was due to the broken map sensor, I've read the map sensor can have an affect on ignition timing. Check Valve lash in a few days. I set it when I put the motor together but maybe its changed a bit. I've already checked fuel pressure, but that was to the feed line not through the fuel filter to the fuel rail side.

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  • Crombie
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29 Sep 2019 13:05 #33916 by Crombie
Replied by Crombie on topic Honda CRX map sensor issues
I rechecked ignition timing is it set at base timing, I read that map sensor does not affect ignition timing only above idle in the mapping tables. I'm going to check for 3 volts at the PCM from the map sensor signal and ground, with the map sensor plugged in. I'm also installing an innovate wideband LM1 this week, as I bought one second hand. I don't know what the fueling is like but it feels and sounds to me that the cars lacking in fuel. I will update in the week, I need to keep persisting with this

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  • Crombie
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01 Oct 2019 15:27 #33961 by Crombie
Replied by Crombie on topic Honda CRX map sensor issues


Its idling at a rich 12.5 air fuel, but it goes lean from quarter throttle upward 14-16, the overrun it drops to 11 rich. So I decided to adjust the TPS after I checked the map sensor off voltage which was 2.9v, and the air temperature sensor was 1.6v approx at around 55F. I checked all the sensor grounds too, though I haven't checked the map sensor ground from another sensor ground, as the battery it drops it to 0.2, when it should be no more than 0.1, so I need to check it from a PCM ground, and the map sensor doesn't share a ground with the other sensors.

I then proceeded to adjust the TPS to 0.42 from 0.48v, I was expecting to see the Idle fuel ratio to go a bit more lean, but its at 11.4 most times now, I thought it meant the PCM would see less throttle and deduct fuel, but it had the opposite effect. Either way when driven again its still lean, but very rich at idle and overrun
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  • Crombie
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01 Oct 2019 15:47 #33962 by Crombie
Replied by Crombie on topic Honda CRX map sensor issues
When the map sensor made it perfect, I think the PCM was fooled for a bit, Im pretty sure the headers warped at the cylinder head, I had header off, had to drop the subframe to change the oil pan gasket, and saw the blow by on the header gasket, thought tightening it more and heat expansion would seal it, but I think this may be the over all problem

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