Hello, I have a 94 Prelude EX (4cyl) that I'm trying to help a friend get running. Thought I'd ask here and seeing if anyone has any ideas. Won't start, has spark but not getting fuel.

When the key is on, the pump is suppose to kick in for a couple seconds, but doesn't. Did a bench test on the main relay and it tested good. Even resoldered the connections just to be safe, but no change.

Jumpered pins 5 and 7 on the Main relay connector and verified I had voltage to the pump when the key is turned on. Applied 12v to the pump and verifed it was working as well.

With the relay in place and the key turned on or in the start position, I'm not getting any voltage to the pump. This would seem like a relay problem, but like I said, it tested good.

Could this relay still be bad in some way or could the ECM be causing this? Since the pump is suppose to initially stay on for two seconds when the key is on, is there a timer circuit somewhere that shuts it off or something?

Thanks,

Michael

 

You probably already seen this link: http://techauto.awardspace.com/mainrelay.html

It has great info.

Is the check engine light coming on then off (self diagnostic) when you first try to start the car? How is the battery power, connections, etc.? (All info. included in the above link.)

 

The check engine light stays on after you try staring it. Attempted to get some codes from the ECM (jumpered the two pin service connection), but its either not going into diagnostic mode, or I'm not doing it right. The light stays on the whole time and never goes out or blinks.

Does the engine have to be running in order to get the codes or are you suppose to be able to retrieve them with then engine off and key on? Also, if you clear the codes (remove the 7.5a fuse) does the engine or ECM record any new ones while the engine is trying to start, or does it only record them while the engine is running?

The battery appears strong and turns the engine over ok. Hadn't checked on any connections or grounds yet. I'll check out the link, thanks.

 

As noted as part of the link: If the Check Engine Light stays on then it's likely that part of the ECU has no power (most often a lack of proper grounding) or a critical device isn't speaking to the ECU. (A dead main main relay can allow the "check engine" light to stay on.)

http://techauto.awardspace.com/ignition.html

The engine does not need to be running for code retrieval, only key ignition to on. If you removed the back up fuse (7.5A) to clear the ECU codes, it probably won't record any new trouble codes as your check engine light stays on right now.

The link has a troubleshooting flowchart too.

 

I appreciate the help. Looking thru the tech pages it looks like I can "bypass" the main relay by jumpering pins 1,3, & 7. I'm guessing this should tell me if my relay is bad if the car then starts?

Just curious on the diag codes, what blink sequence is zero?

Tommow I'll check out all the ground connection and clean up the battery terminals as well. Looks like I also need to verify some of my sensors are working too.

I was thinking the ECM was bad, but would like to be sure before purchasing one.

 

If you are talking about Diagnostic Trouble Code, DTC 0, as shown in the Honda service manual, that refers to the check engine light never coming on (even for two seconds) after the ignition is turned on and may be an ECU problem.

If you are talking about for example DTC 10, 30, etc., it would be no short blink sequence, only long blink(s).

Codes 1 through 9 are indicated by individual short blinks.

Codes 10 through 43 are indicated by a series of long blinks and short blinks. The long blinks equal the first digit, the number of short blinks equal the second digit. However, with code 10, 20, and 30, you would just see the long blink(s) (first digit) and no short blink (second digit).

 

That was I was needing to know. Thanks again.


Michael

 

Hi guys, I kinda have a similar problem, my car won't spark. Changed coil, ignitor and even tried another ecu, but nothing. Out of desperation I tried a distributor from my friends working prelude and his computer but no spark still....I didn't check the main relay though, what you think?????

 

Having the same problem with my 94 accord Lx 5spd. What all grounds should i check and where are they all located?

 

Well it looks like the ECM was bad after all. Not being a 100% sure this was the problem, I was hesitant to purchase a new ECM and then find out that wasn't the issue.

Didn't think most stores let you return electronic parts like this and didn't want to get stuck with a three hundred dollar part that he may not of needed.

So I had him take it to a local independant Honda repair shop. They replaced the ECM. Parts and labor was only $350 which wasn't too bad.

I considered buying a used ECM, but then if its bad too, what then? I know its no fun troubleshooting a problem with a new part that you assume to be good.