So i've been driving the CRX for about 4 or 5 months and the car ran fine but never would build any heat. so i ordered a new thermostat since it would be nice to help defrost the windsheild on those cold mornings. i pulled it into the shop pulled the 2 10mm bolts, pulled out the old thermostat that was clearly shot, installed the new and filled the radiator and reservoir tank and took it for a spin. I had already warmed it up in the shop and now the temp gauge ready nearly half way nothing was over heating and took it for a spin. The car has a major lack of power and does not pull like it did prior to this.

Is there something in the short term or long term fuel trim that is causing this. double checked to make sure i didn't bump any wiring and i see nothing changed. if need to, i thought about pulling the thermostat and running with none to confirm that it made the difference.

Anyone have any thoughts on this or how to reset the computer if driving with the bad thermostat and not building any heat affected the computer learning?

Thanks in advance!!

 

I will also add, it is a D15 non-vtec manual trans with 323k miles

 

Any CEL codes?

Does the power return when the engine is cold?

Does the power return if you unplug the O2 sensor?

 

yes code 13. I did not unplug the o2 sensor. I put a new one on 2 months ago with a header and full exhaust because there was no o2 and exhaust was rotted.

does still seem to run best when cold. Obviously not trying to beat on it cold though.

is that something I should try. I will check again for any other codes on the ecu

 

Replace the ECU.

Try unplugging it and driving the car when the engine is warmed up. More power?

 

do you know for sure which ECU it should have? I will look tomorrow but when I first got the car I believe what I looked up on the Internet versus what it had was different.

 

Do you have the D15B2 engine? If so, it uses the PM5 ECU.
http://www.phearable.net/information...daeculist.html

 

This is whats in the car and has been even when it was running ok

This is a stack of ecu's that I have from when I was in Honda's years ago

I unplug the O2 sensor and drove 20 miles to town and it is getting terribly bad. I even got a few I even got a few backfires from it it was that bad.
Yes the motor is the D15b2

could it be something to do with a coolant temp sensor? I know on newer cars that really affects the computer

 

http://www.phearable.net/information...daeculist.html

A PR4 ECU is for a 91 Integra DOHC B18 engine not a SOHC D15 engine.

Install the correct ECU.

 

i did go out and try both PM5 ecu's in the car and 1 tried to start and the other did nothing. put the PR4 back in and fired right up and revved up fine.

i did this before and got the same results when i first seen the code 13 and needing a new ecu. at that time i was just trying to clear the code from the ECU.

maybe i should touch on some other issues with the car that i really never thought about until now because i have just been dealing with them and kinda has been second nature.

when i start the car it immediately idles at around 400-500 rpm real low. when i back up (without warming the car up) it will try and die each time i let off the throttle and has a major dead spot when i go down to my corner (1 block) in second. i turn the corner with no throttle and when i go back 1/3 throttle lets say it will just fall on its face for a second or two and then take back off.

i will add some pictures of some things that i believe are missing in the engine bay as well. please give me a minute to do this. maybe they relate to the issues maybe not. i'm just trying to think of anything i have dealt with over the past 5 or so months and just been driving it.

all the stuff i am mentioning was before the thermostat change the other night creating the new issues.

also, today when driving back home, i really got on it and it seems ok at WOT but when trying to cruise and give it throttle is when it really bogs out. i can't even go down a road on a slight incline i mean minimal and have to shift down if someone is on my a$$.

let me get pictures and if you have any other thoughts please let me know especially on the ECU situation if you have any.

thanks!!!

 

i did also spray carb cleaner around all the intake hoses to see if i had a vacuum leak possibly causing the low idle issue. found nothing there

 

Try unplugging your engine temp sensor and see if it runs any better. If those short out for some reason, the ecu will thing it's over temp and pull fuel - might be why it's boggy and idling low. Just unplug and see if it's any better. Also make sure that none of the wires for that sensor are touching, that'll tell the ecu the same thing. Kinda common with our old cars and brittle wires. Also might explain why it's ok at WOT because the ecu ignores some of the sensors and goes off it's programming.

 

Also, the 2 plugs in your last 2 pictures don't go to anything on your current engine - both are EGR/Emissions stuff.

 

Check your thermostat ground too!!

 

Have either of the PM5 ECUs been tested to show that they are known good?

Your number 1 priority should be to install a known good PM5 ECU in the car. Then go from there.

 

A PM5 ECU won't work - he's multipoint, not dual point.

 

I missed that it's a HF CRX. How hard is it to revert to dual point so that the correct ECU can be used? The engine will never run correctly on the PR4 ECU.

 

Converting to dual point I don't think is the issue. He should be able to use a pm6 ecu or the stock hf ecu (don't remember the ecu code). He also said it drove fine before changing the thermostat, so ecu isn't a concern for his issue - something changed when he swapped the thermostat. I'm guessing either a wire on the temp sensor or maybe he didn't get the ground wire back on the thermostat housing. The code 13 is an odd one, but I've seen it before with the older ecus. If memory serves me correctly, the 88-89 civics had the barometric sensor outside the ecu to right of the glovebox. It looks like some work has been done to the car, it's possible the sensor could have been removed or unplugged - it looks like a map sensor. A 90+ ecu (I believe 90 was the switch over year but could be wrong) would eliminate that issue because the sensor is inside the ecu.

 

The PM8 ECU for the HF will look for sensors not present on the D15B2, and is designed for a fuel efficient multipoint D15B6 SOHC engine (62 HP). The PM8 should not be considered an option here.

The PM6 ECU for the Si is designed for the multipoint D16A6 SOHC engine (105 HP).

The PM5 ECU is the correct ECU for the dual point D15B2 SOHC engine (93 HP).

It's doubtful that the D15B2 engine actually ran fine on a PR4 ECU made for an Integra B18 DOHC engine.

 

Ok, so FINE probably isn't the best way to describe it. But he said it ran way better than it is now "after" the thermostat change. Yes the PM5 would be the correct ecu for his engine IF it was stock, but it's not, if you look at his pictures he has a multipoint intake manifold, the pm5 will not run 4 injectors hence why I said the pm6 ecu.

 

OP could likely buy the correct dual point IM for pretty cheap.

 

Why convert back? That's basically the reverse of an mpfi conversion - that means new ecu, new distributor, removal of 2 injectors, rewiring distributor, remove and rewire of resistor box. His issue isn't the ecu - again I repeat - the car ran good with a lot more power than it has now before swapping the thermostat, and now it doesn't. Replacing the whole fuel injection system seems a little extreme does it not. It's way more likely that something didn't get put back together correctly or he broke/pulled a wire on a sensor.

 

My suggestion for the PM5 ECU is based on the fact that the PM5 ECU is the perfect match for the D15B2 engine.

FYI: The dual- to multi-point conversion involves installing a crx si (D16A6) head on a D15B2 block.

Haha

 

At the risk of inspiring a fishing expedition, my only experience with a code 13 was not the actual sensor (this is on a "1990" hatchback with a nightmare hackjob wire harness), it was the reference voltage wire from the ECU. The wire broke somewhere in the dash harness and was intermittently shorting, causing all kinds of hell for the engine. It only threw a 13 until I unplugged the barometric sensor (I have the external for some reason), at which point it threw codes for every sensor fed by that ref voltage. Ran a new wire from ECU to the baro sensor and engine harness, and suddenly she ran like a top. For a while.

TLDR: Get a multimeter and wiring diagrams.

Uh, muellersfan, A6 head why? I've done two MPFI swaps using the B2 head... they're practically identical.

 

You don't have to put a d16a6 head on a d15b2 block to do the mpfi conversion. The mpfi conversion only relates to the injector setup - dual point (2 injectors) to multipoint (4 injectors) - where in there do you have to change the head? They have the same intake bolt patterns, same castings actually - the only difference is the cam that cam in them.