pgm-fi light/backfire

[jt77]

Please help. I just bought my girlfriend a 1985 honda civic crx. i'm told it's not the original engine. i think this one is a 12 valve. well, anyway, after about a week of driving it with low grade gas (not sure if this makes a difference) i was told the last owner used high octane gas, and now, the pgm-fi light comes on after about 20 seconds at idle. it will only idle if my foot is on the gas pedal. it bogs down at stop lights, and dies. if i get it to run, it backfires the whole time while i'm driving it. it was going fine, then started backfiring, and wouldn't reach over about 20 miles/hr. HELP ME...PLEASE

[Yawbo]

I recently was told I had low compression on a cylinder and that I needed a new head/engine. I had the exact same problem. (this may/may not be the actual problem) Check your compression. And also let me know if you found the same thing because I don't know if that diagnosis was correct.

[jt77]

how do i check the compression? i work on airplanes, but really don't know much about cars. also, there are some lights on under my passenger seat. WTF?

[Figori]

If you reply with what numbers were lit up (2-4-6-8), I can tell you the diagnosis code. Those are from your ECU. Just post the numbers lit up, and I'll do my best to give you an explanation.

[Yawbo]

To check the compression on a cylinder, I know you need a compression gauge, then you remove a spark plug/all plugs? and crank the engine with the gauge attached. Something like that. I would search around to get an explanation from somebody who's done it before.

The lights under the seat are the trouble codes from the ecu. Take a look at this post. It tells you what the codes mean.

[jt77]

o.k. i was just at the car, and i have a mallory coil. the wire from the coil to the center pos. of the dist. cap was sparking at the dist cap side out of the wire, when the car was running. i also looked at my numbers under the seat, and the numbers listed are 1,2,4&8. 1&4 are lit up. btw...i can't get a new wire today, as kragen and auto zone don't carry them, and the only other store in my area that i can get one made at is closed for labor day.

[Figori]

7. 0 4 0 1 ____ Hesitation, fuel fouled plug or engine stalls frequently
7. Check for disconnected MAP sensor vacuum hose.

That is a direct cut and paste from the post above. Just in case you were wondering.

[jt77]

next...what is the MAP sensor? if i can find this, the vacuum hose should be no problem. once i find this hose and replace my coil wire, is there anything i need to do to like reset the computer? if so, how would i do this?

[Figori]

The MAP (Manifold Absolute Pressure sensor) is located on your firewall directly beside the vin #. There should be a vacuum hose going from it to the throttle body. Make sure it isn't cracked.

Hope this helps. If all else fails, find an autozone and buy a manual. That's basically where I'm getting all of my info from.

[Yawbo]

Just a follow-up; A friend who's a mechanic took a look at my car yesterday. We checked the compression and it seemed ok. So I think it's a safe bet that the shop I took it to was lying. I'd cross compression off my list. But it wouldn't hurt to have a look at your spark plugs, if you don't find anything going on with your MAP sensor. My friend also suggested it might be the TPS, if we have those in our cars...he says newer ones have them. There's an 87 crx service manual too if it will help you. My car is having the same problems so I hope you figure yours out so you can tell me what fixed it.

[Yawbo]

By the way, to check your compression, you remove all the spark plug wires (make sure you keep track of where they go for putting them back) and then remove the spark plugs. Then just screw the lead from your compression gauge into the spark plug hole for one cylinder, and crank the engine, you'd measure compression based on the 3rd tick of the gauge. Then you just clear the reading, remove the lead and repeat the procedure. That's how we did it anyway.

[Yawbo]

Resetting the computer:

In the main fuse box (below the steering wheel, on the left side) you'll want to disconnect the hazard fuse. If you keep it disconnected 30 seconds that should be enough time. This clears the trouble codes stored in memory.

I think you might also want to check and make sure you don't have any vaccum leaks. Look for vaccum wires on the throttle body, intake and there's one hiding (something like) below the intake manifold and above the starter. I think I remember having a problem after doing a clutch and my engine wouldn't idle either and that fixed it.

[jt77]

wow. it works. i just looked for the MAP sensor vacuum hose, and found it disconnected. i reconnected it, and it works like a champ. i also replaced my coil wire since it was bad. i just want to send a big thanks to everyone who helped me through this problem.

[Figori]

No problem! Glad to hear it works! Can't wait to get my 87 rex si up and humming...