Coil Problem after doing compression check
 

Hello, I'm new here to this Forum, and would like to ask for some advice.

1990 Honda Accord LX fuel injected, 5 sp manual, 265,000 miles

I just performed a compression test (good results, 156 - 160 psi for all 4).

Now, the car won't run, whereas it ran fine before I did the compression test. I'm not getting any spark. I checked the coil and found that the secondary ohms is low (11.3 ohms, and should be about 13.5 ohms minimum). I guess I must have damaged the coil when rotating the engine for the compression check. I had all 4 plugs out, and the spark plug wires disconnected, but I did not pull the distributor cover or disconnect anything with the coil -- maybe I should have.

So, I will go buy a new coil. My question is, are there other components that I may have damaged during the compression check, due to not disconnecting the coil?

Thanks for your assistance.

Alvon Elrod

RE: Coil Problem after doing compression check
 

I have no idea if what you did wrecked the coil (I doubt it, but there are other more delicate electonic parts in the ignition), but I do know that it's a very good idea to ground out all the leads if cranking the engine without the leads installed on the plugs.

RE: Coil Problem after doing compression check
 

I usually pull the fuelpump fuse & unplug the distributor - that disables both fuel & spark. What you did usually doesn't damage stuff, so Iguess you were just lucky.

RE: Coil Problem after doing compression check
 

Also I doubt you'll ever know if the compression test really did damage the coil. Maybe it was going to die anyway and it is just a strange coincicence that it happened during/after the compression test. You aren't running Bosch spark plugs are you?

RE: Coil Problem after doing compression check
 

I'm running the stock NGK plugs. I just finished a timing belt/water pump change. Also replaced seals (Crank, Cam shaft, balance shaft, oil gear assy), all belts, plugs, rotor, cap, air filter. Everything ran great afterwards, and drove it 100 miles, then decided to do a compression check just for curiosity sake.

I read the Haynes manual recommedation to disconnect fuel pump fuse (read chapter 4 it says, yeh right, I looked thru the whole chapter and didn't find anything about a fuel pump fuse, so I gave up looking for it), and to disconnect the coil secondary, I think it said (read chapter 5 or 6, it told me -- I spent enough time reading and searching for info, so I just went straight to checking the compression). The compression numbers looked good, but the engine wouldn't crank afterward. I pulled a plug out to look for spark. No spark. So checked the coil next (back to that darn Haynes manual!), and found the secondary resistance to be lower than the recommended range. I hope there is nothing else fouled up.

Would the secondary resistance reading of 11.3 ohms be bad enough to cause the no spark issue? I'd hate to buy a new coil, and find that the problem is not in the coil.

Thanks again for your inputs, guys.

Alvon

RE: Coil Problem after doing compression check
 

I have been told by a deserthonda (one ofour Honda Techs - currently on vacation)before that a coil is sort of a difficult gremlin to check. The old fasioned method of using a VOM can be inaccurate he told me. Hopefully one of the experts will get on here and shed some light. We have a new master tech (HondatechAV6) that joined recently. he has been on here answering a decent amount of questions. If he doesn't see this thread and respond here, if I were you I'd send him a PM and ask what is the best way to test a coil.

RE: Coil Problem after doing compression check
 

There's more than one way for a coil to fail. Measuring resistance through each circuit (primary & secondary)is a good way to test for ONE of them.

If that resistance is OK, you still need to check for a short to ground. Butthe coil's insulation can break down at high voltage. With a normal ohm-meter it'll test OK for short-to-ground. The insulation doesn't break down at the low voltage of a normal multi-meter. Gotta use a $$$ device that'ssorta likean ohm-meter that operates at high voltage.

RE: Coil Problem after doing compression check
 

Sounds like I need to replace the coil, based on the measured secondary resistance, even if it checks out OK in other respects. I'll check into getting a new one . . . unless somebody out there has a known good used one that they would like to offer to sell???

Alvon

RE: Coil Problem after doing compression check
 

I would have thought that 16% low coil resistance might have caused misfires or some problems (from a weak spark).So if you takethe plugs out & check for spark you get a weak spark? Or NONE at all?

RE: Coil Problem after doing compression check
 

Jim, thanks for hanging with me on this one. I'll check again tonight when I get home. When looking for spark last night, I was in a brightly lighted area, and may not have noticed a weak spark. I'll repeat the test with lights off. I'll also try to see if I'm getting a signal going to the coil. Maybe the problem is upstream of the coil.

Alvon