gdrew888

Hi All,

Cylinder number 1 is dead, not firing.

It has 175 lbs compression.

Lead wire and spark plug are working and confirmed by swapping with other cylinders.

Fuel injector was exchanged with another cylinder and confirmed working.

Fault code is 16 - 1991 Accord Automatic Trans.

Is it possible the injector solenoid is not getting its signal to open? Is there a way of confirming the voltage is getting to the solenoid?

Any other possible issue?

Thanks!

tech8

Since swapping injector with a good one doesn’t change anything, we’ll presume the injector is good.

1. Unplug the 2P harness connector to injector no. 1.
2. Turn ignition ON.
3. Measure the voltage on the harness connector side. Voltmeter’s red lead on Red/Blk wire and voltmeter’s black lead on body ground. Is there voltage?
4. If there is voltage in step #3, then touch the voltmeter’s red lead again on the Red/Blk wire; but, this time touch the voltmeter’s black lead to the 2P harness brown wire. Is there still voltage and is it about the same voltage measurement as in step #3?

gdrew888

Yes I got the roughly the same voltage in step 3 (11.63 volts) as I got in step 4 (11.58 volts).

Thanks.

tech8

The code 16 may actually be due to a faulty main relay. See this two links:

When the Main Relay goes bad

http://webcache.googleusercontent.co...&ct=clnk&gl=us

Check the main relay, many times you can resolder cracked solder joints and have it okay again.

Give that a try, not sure if that may resolve your entire issue.

gdrew888

Ok, I'll check out the main relay. Not 100% sure where its located, didn't look like it was in the location that was shown in the video.

tech8

This photo is of the main relay for your 1991 Accord.

This other link also shows the location.

http://webcache.googleusercontent.co...&ct=clnk&gl=us

gdrew888

Thanks for the info tech8! Found the relay and got it out no problem. The solder joints looked like they were in really good condition but I touched up a few of them anyway. Its getting too late tonight to put the relay back in so I will install tomorrow after work and let you know how it went. Have a good night!

gdrew888

I got the main relay installed this morning before heading off to work but still not having any luck getting cylinder number 1 to fire. I checked the spark on the plug again when it was out of the engine and I get a hot white spark. If I fire up the car with all the plugs in and run it for a minute then pull the #1 plug out it looks like it is wet with gas. I'm still at a loss...I have spark, compression, gas and I assume timing because the three other cylinders are running. Not sure where to go next with this...

tech8

Is Code 16 still present?

gdrew888

Yes sir.

tech8

1. Code 16 is usually due to ECU not receiving power from the main relay.

The main relay actually consists of two relays inside:
• one relay supplies power to the ECU, fuel injectors, and Electronic Air Control Valve (EACV)
• the other relay supplies power to the fuel pump

2. When you did the tests I wrote up in post #2, your results found power (+) at the Red/Blk wire. This would indicate that the main relay did supply power to the injector.

What this would leave me to conclude is the code 16 may possibly be due to a faulty ECU or a lesser chance of an open (break) with the Yel/Blk wires that come from the main relay to the ECU. The Yel/Blk wires from the main relay goes to pin 1 of ECU Connector C435 (16-P gray connector) and pin 13 of ECU Connector C434 (26-P gray connector).

The ECU controls the fuels injectors by supplying the ground (-) source. Although your results from the test from post #2 showed ground present on the Brn wire (which comes from the ECU), there is the possibility the ECU is not consistently sending the ground signal to injector #1.

3. You can always open up the ECU and take a look to see if there are any damaged resistors, capacitors, board burnt, etc. Even without seeing anything visually, the ECU can still be faulty. So can't be sure if ECU is faulty or not from visually inspecting if there isn't anything obvious.

gdrew888

Great write up and explanation tech8! Is the ECU the box under the floorboard passenger side beside the TCU?

Thanks,
Gene

holmesnmanny

I would check for continuity from the 3 injector ground side back to the ecu connector while wiggling the harness.

tech8

Yes, the ECU is at the location of the passenger side you mentioned. You can also test for power (+) on the Yel/Blk wires going pin 1 of ECU Connector C435 (16-P gray connector) and pin 13 of ECU Connector C434 (26-P gray connector); with ignition ON.

gdrew888

I have a spare ECU from a 1993 I will try first, just not until tomorrow after work. I'll let you know the results and go from there. Thanks!

gdrew888

You are good!

I put the replacement ECU in the car tonight and I now have all 4 cylinders firing. Great news right?

Well yes, that confirms I must have a problem with the original ECU. However, the replacement ECU is causing the dreaded pulsing idle problem low & high revving with a lot of exhaust smoke.

I opened up the original ECU with the misfire on the no 1 cylinder but cant seem to see any bad resistors, capacitors or solder joints.

Do I need to locate another ECU? Will one from a standard car of roughly the same vintage work?

Thanks,
Gene

holmesnmanny

It's possible the pin out for the 91 vs the 93 ecu is somehow different. Go grab a used 90-91(preferably 91) auto ecu from the junkyard. These cars are a dime a dozen at the junkyard.

gdrew888

So I took the original ECU apart again only this time I took it completely out of the case. I wanted to give it one more good going over before I gave up on it. I sprayed it down with electrical contact cleaner and blew it out with canned air. I also cleaned the pins and plugins using the same method. I put the box back into the car and gave her a test fire and YES all four cylinders were firing! I took a few minutes for all the smoke to clear from the exhaust and all the sensors to start reading correctly. I took it for two test drives yesterday and all seems normal. My son is taking it to work today so I'm hoping whatever was wrong doesn't go wrong again. I never would have guessed the ECU could have caused only one cylinder to misfire. Thanks for all the great advice and assistance in this matter! Happy Easter!