91 Civic Trouble

dude911 · #1 Jun 30, 2006, 10:16 PM

Hello,

I am working on a 91 Civic DX hatch, 1.5 in our shop, a GM dealer. The tech working on it is somewhat familiar with the car but we cannot figure out what is going on.

First of all it has what seems to be the common code 16. Initially it would run bad on hard accel, but progressed to the point of stalling and then a very long drawn out starting procedure had to be done. The customer mentioned that sometimes cycling the ignition would get it to restart. We replaced the cap, rotor, wires and plugs, as well as the fuel filter before beginning the task of the 16 diag chart, all to no avail. Actually it seemed to run great, but if you stabbed the throttle to quickly it would bog down, backfire and die. It has good fuel pressure, but now it idles rough as well.

Anyway we went through the diag chart checking various things along the way until we were led to the replacement of the ECU, which I dont have a problem with if it fixes the car, obviously. My concern is that we arent sure it is going to fix it and I have found prices range from low 200's to 1000 dollars, and all have to be ordered, a little to much to guess with. Can anyone give me any advice, are there things we are missing, or is it to the point of ECU replacement and crossing our fingers? Any help appreciated.

dude911 · Jul 1, 2006, 09:00 AM

Quote:

Originally Posted by txgreasemonkey

Have you tried this, yet?

For DTC 16, start engine, allow it to idle, and listen for the clicking sound from each fuel injector, using a mechanic's stethoscope. Turn the ignition off, disconnect the 2P connector from the fuel injector that does not click, and measure resistance between the 2 terminals of the fuel injector. Is there 10-13 ohms? If NO, then replace the fuel injector(s) that are not 10-13 ohms. Turn the ignition switch ON and measure the voltage between YEL/BLK (+) terminal in the 2P connector and body ground. Is there voltage? If NO, then repair open in YEL/BLK wire between fuel injector and the main relay. If YES, turn the ignition switch OFF, reconnect the 2P connector to the fuel injector and measure for voltage between A23(-) and the pin for each injector (No. 1=A1+, No. 2= A3+, No. 3=A5+, and No. 4=A2+). Is there battery voltage? YES, substitute a known good ECM. NO, repair open in wire between ECM (A1, A3, A5, or A2) and the fuel injector.

I know he told me he checked the fuel injectors and they are working properly, he also said he removed the iac valve and it was full of buildup. Cleaned it but no change. We are at the point of EcM Replacement but I was just wanting to be sure.

-----------------------------------------------------------------------------------

Quote:

Originally Posted by txgreasemonkey

Try this next:

Disconnect 3P MAP sensor connector, turn ignition ON, and measure the voltage between the connector's reference wire (probably YEL/GRN)+ and ground. What voltage did you record?

I dont know for sure if he checked this or not, but I dont see that step on the diag for code 16, is that something you have seen that can cause the issue?

dude911 · Jul 1, 2006, 11:48 AM

Quote:

Originally Posted by txgreasemonkey

This simple "K Test" tells you whether the ECM is delivering 5 volts to the MAP sensor, the "key" sensor on Hondas. If it is not, chances are your ECM is bad. If the MAP sensor doesn't get the necessary voltage, it can cause catastrophic failure on Hondas, affecting ignition and fuel. The MAP sensor controls timing and air/fuel delivery on Hondas. Make sure the MAP sensor is functioning properly, as well, on both the electrical side and vacuum side.

Honda ECMs are starting to go on vehicles over 8 years old. It's a bigger problem then many are willing to acknowledge. They are not "bullet proof," as some would try and lead you to believe. Odds are that if you don't replace it now, it will have to be in the not too distant future. I've already replaced the ECM on my 1993 Civic DX and it lives a "charmed life."

Good deal, thats the kind of info I was after. I am a service advisor at a GMC dealer so my knowledge is mainly directed at GM vehicles, although the basics remain the same across the board. I will have that sensor/circut checked. One last question, you say if the map sensor isnt getting the correct voltage etc. etc. The ECM supplys voltage to the sensor, so if the sensor is getting the right voltage, is the ECM good, and the sensor bad? Or could it be both, shouldnt a code set for the map sensor if in fact its bad?

dude911 · Jul 1, 2006, 05:12 PM

Quote:

Originally Posted by txgreasemonkey

To directly answer your question, if the sensor is getting the right voltage the ECM has only proven itself for this test. However, this is the most crucial test it must pass, since failure can be catastrophic for the ignition and fuel systems even working.

Both the ECM and the MAP sensor could be bad. Like ECMs, MAP sensors are, generally, very reliable components. Both are very expensive items to replace, so thorough testing is imperative. New MAP sensors from Honda cost approx. $325. You are right that a code 3 (electrical) and/or a code 5 (vacuum) would normally be set for a failing MAP sensor.

I appreciate the help, I will make sure that the circut gets checked. The tech working on it is a master GM tech in all areas except body, as well as a Mazda Master Tech, so I kinda feel bad for going behind his back and asking, but it doesnt hurt. What is your opinion of buying a ECM for this car through, say, auto zone, versus the dealer. The is a HUGE price difference of course.
My feeling, since they require a core is that they were at one point Honda ECM's they they refurbish, so I guess it's a matter of the quality/skill of the tech doing the repair. If it were only a few dollars I always recommend staying with OEM, but we are talking approx 700 dollar price difference between Honda and Autozone.

dude911 · Jul 1, 2006, 09:28 PM

Quote:

Originally Posted by txgreasemonkey

Miscellaneous thoughts:

A. Did you check the timing? It could be retarded too much.
B. Did you install NGK plugs? I haven't seen cross-reference plugs work well in Hondas.
C. Did you clean the injectors? Try Regaine in the tank.
D. Did you adjust the idle speed to spec.?
1. Start the engine and warm it up to normal operating temperature.
2. Connect a tachometer, normally to the BLU wire coming from the distributor. It is often buried in the cluster of wires near the master cylinder reservoir. Can be difficult to single out, because Honda does a great job of hiding it. I eventually found mine.
3. Disconnect the 2P connector from the Idle Air Control (IAC) valve.
4. Start the engine with the accelerator pedal slightly depressed. Stabilize the rpm at 1000, then slowly release the pedal until the engine idles.
5. Check idling in no-load conditions: headlights, air conditioning, etc. not operating.
6. Adjust idle speed to spec. (normally 450 rpm). The idle adjustment screw is "leaded in," to prevent owners from adjusting them. You will find it on the top end of the throttle body. Take a small screwdriver and remove the lead seal and make your adjustment.
7. Reattach the 2P connector to the IAC valve and everything should be fine.
8. Disconnect negative battery terminal or pull fuse to reset ECM.

A: Yes, that was actually the first thing we did because about 400 miles ago we replaced the water pump and timing belt.
B: We put Denso plugs, the placard under the hood has three types listed with #'s, they match.
C: No, didnt clean them initially but they were taken out and inspected and all looks ok.
D: No, but its worth a shot. Another thing, the ecm to my knowledge has never been "reset" will that change anything other than erasing the code?

PAULIE · Jul 4, 2006, 12:24 PM

could the ecm be the reason my cooling fan isnt coming on? I also have a 91 honda civic 1.5L, but mine is a dx 4 sedan giveing almost the same kinda trouble as well

dude911 · Jul 4, 2006, 03:37 PM

Something new that we noticed yesterday, the IAC motor runs all the time if the key is on. Does that mean anything. By the way we checked tha map sensor and its getting 5v and operating to spec.

dude911 · Jul 4, 2006, 04:25 PM

Quote:

Originally Posted by txgreasemonkey

I would think that is normal. Were you successful in following the procedure and reseting the idle speed? Are you going to replace the ECM?

No the car wont stay running now, it starts and idles ok, after a minute or so it sputters out and dies. The ecm will be replaced soon, I'll let you know how it turns out.

PAULIE · Jul 6, 2006, 10:22 PM

Ok,can somebody please tell me where the ecm is on a 91 honda civic dx?

dude911 · Jul 7, 2006, 04:52 PM

Quote:

Originally Posted by PAULIE

Ok,can somebody please tell me where the ecm is on a 91 honda civic dx?

Passenger side under carpet between botom of dash and floor.

Anyway I ended up taking the Civic to the Honda dealer down the road from us, I figured it was worth the $80 to be sure it needed a ECM. Turns out it had a bad ignition igniter and coil, which is internal to the distributor, and an intermittant main relay. I went ahead and let them do the work, that way if it didnt fix it I had them by the balls. Picked it up today and it runs like a top.
Thanks for all your help greasemonkey, it got us in the ballpark anyway.



At Ask Me Help Desk you can ask questions in any topic and have them answered for free by our experts. To ask questions or participate in answering them you must register for a free account. By registering you will be able to: Get free answers from experts in any of our 300+ topics. Accept money for answers that you provide. Communicate privately with other members (PM). See fewer ads. Sign Up!