So this is my first DIY build and I'm almost there just can't solve this last piece of the puzzle and neither can my mechanic... Here's where I'm at

96' Spec JDM B18C in a 91 CRX Si.

I was using the stock OBD2a ecu but recently acquired a chipped p28 with the 96 ITR basemap. Both ECUs would do the same thing when starting. The car would start run for no more than 2 seconds then die. If you tried to start it again the car would run for a fraction of the initial time it ran then die again almost immediately.

With the map sensor unplugged the car starts and runs just extremely rich. I've searched all over for a solution and have found tons of similar stories on a bunch of different cars but never have found any conclusive solution.

The car won't run long enough to through any codes at this point and the codes that the obd2a ecu threw were 20 and 41 but that was only when the MAP was unplugged so i couldn't imagine those are steering me in the right direction considering no code pertaining to the MAP has popped up yet.

The Kickers:
Tried multiple good MAP Sensors
Already replaced the O2 Sensor
I did this early on and have switched back and forth with both ECUs

When everything is hooked up correctly, car starts, tries to run and then dies. It will immediately die if i try and give it gas on the first attempt.

IM Stumped and I've reached the ALL IN point on this one so I need to make it work.

Thanks in advance to any suggestions.

 

Do you have the TPS and MAP plugs switched? In other words, is the TPS plug hooked up to the MAP and vice versa? If you are sure that the plugs are not switched, then double check the wiring to the MAP with the pins on the ECU plug. Its very likely that your problem is either one or the other.

 

Nope, I traced them back to the pinouts to 100% confirm they're right. I had switched them around the first day we got it running thinking thats what the problem was. it ran basically the same as with just the map unplugged. i think its just in loop mode when the map is unplugged or the plugs are switched. There is no chance the plugs are incorrect though. This is killing me though....

 

Just remembered too I have a PLM Header
https://www.privatelabelmfg.com/prod...-v2-header.htm

I saw somewhere else that the placement of the O2 bung may cause a weird reading to the O2 though i doubt this would cause the start and stall...

 

Hmmm. Did you check the continuity of the MAP wires from the plug to the ECU, and are you sure that each individual wire is in the correct pin? I know that is a redundant question, but if there is a continuity issue between the plug and the pin, then the signal would not be right or if one of the wires is switched, then the signal won't be right.

It should run rich when the MAP is unplugged, so that sounds "normal", but when it is plugged in is when the abnormal symptoms appear. Basically, when it is hooked up the car will start but wont run for long and will die immediately when you give it gas. That is not normal. It seems that your problem is just with the map sensor which is 3 wires and an o-ring. I would check the actual sensor (which you know is good), the o-ring, and the wires, other than that I have only one more idea.
Sometimes a vacuum leak or some other type of intake manifold leak (which is technically a vacuum leak) will cause the same symptoms of a malfunctioning MAP sensor. There are plenty of ways this problem could arise so it may take some time to check that throughly.

I hope you get this figured out. Good Luck!

 

Yea i was thinking it may be vacuum somewhere i was looking all around today for one didn't really find anything but i'll check again. i'll check continuity too and rule that out. thanks though for the ideas.

 

In order to go back and forth freely from the obd2 ecu to the obd1 you would need to change up the distributor wiring(or using a rywire distributor/crank sensor conversion harness etc etc). Are you doing that or are you just unplugging the conversion harness and plugging in the other ecu ?

Did you run the crank sensors and wiring along with the obd2 oil pump ?

 

I used a obd2a-0bd1 distributor and alternator conversions, and an ecu obd1 to obd2a conversion harness so i could get the stock ecu to plug into the obd1 harness. Wiring along the oil pump???? Not sure what wiring i should be running here??? I can always just use another distributor here instead of using the conversion harness too.

 

pretty sure there is no crank sensor on the 96 spec ITR. OBD2a was my understanding that it when they first switched to it in Japan was basically still OBD1. Not any additions in sensors in JDM just different plugs. Plus the car behaves EXACTLY the same with either obd2a P73 and obd1 P28 ecus plugged in.

 

Obd1 and obd2 distributors and alternators work the same,really only difference is the plugs. Obd2 motors have an added crank sensor but jdm motors don't.

Op how did you test the wires? What location on the ecu did you check the map wires at?

 

i haven't done continuity test yet. i just made sure they were going to the right pins. They are correct in the correct locations i can't remember what pins they were though. D11 + D7 i think for the TPS and map.

 

Are you using the MAP on the firewall or the throttle body one?

 

TB factory one for the motor.

 

Still no luck here or even a good place to start.

 

Sounds like you are going to have to pay a tuner shop to fix it for you.

 

Jdm obd2a ecu or usdm?

 

JDM I don't believe there are any obd2a USDM ecus that Honda used.

 

Sure there are but perhaps not for integras.