I was having a rough running/stumble that disappeared after installing a new coil.

That was a couple days ago.

50 miles later the car is running worse than ever.

Starts and idles great but hit the gas and it starts backfiring, stumbling, and eventually surging. If I floor it the engine smoothes out after a couple seconds and runs strong while at high RPMs.

So I put the old coil in and it runs much smoother!

New plugs, wires, cap, rotor.

Any ideas?

Well I'll be damned, a loose wire at the ignition amplifier connector!

I have a sneaking suspicion that the tech that last worked on it broke it.

When I went to look at the ignition amplifier (IA) I noticed that the boot was pulled back and wires exposed.

I disconnected the connector from the IA and noticed that the #5 wire was pulled back slightly in the connector. I pushed it forward into position but it did not "click". The connector has been broken and the #5 wire does not clip into it anymore. The wire probably made *some* contact but intermittently missed, which is exactly how it felt driving it.

I removed the screws on the IA mounts, pulled it off, made the connection by pushing the wire into the connector from the back so that it would clip onto the male end and stay put (at least until I get to the junkyard and replace it).

So far it has run perfectly, even with the new Bosch coil that was giving me trouble. Which I must now apologize for calling "junk" or some similar word.

Hopefully it holds up and I can start rebuilding my confidence in this vehicle.

Thanks for all of the help, suggestions, and humor along the way!

OH FOR CRYING OUT LOUD!!

It's back!

How the hell did plugging in that one wire fix it right then and there.

Now it runs horrible.

Check the wire again, reinsert, everything looks good, still runs like crap.

I've about had enough.

Feeling your pain brother.Not sure if your car has a power stage module on drivers side fender wall.I had similar problems years ago.The guys at Voluparts in Atlanta gave me a used one and it worked.Take a look in the FAQs part of this site its located in the search pane at top of page.It'll help figure it out.

Put the power stage in from the junkyard and she's running perfectly.

However, I think this is the third time now that this has happened so I'm won't be too optimistic until I've got some more miles on.

I'm surprised the Bentley manual doesn't have this test in it, very simple.

Thanks to Fred Su at StepByStepVolvo dot com for the excellent instructions!

You could improve your chances with the junkyard power stage by taking it off it's heatsink, cleaning off the old compound and applying a fresh layer. See Radio Shack for the compound, which is essential for maximum heat transfer. Heat is often the cause of power stage failure.

--
Bruce Young, '93 940-NA (current), 240s (one V8), 140s, 122s, since '63.

Thanks for the tip.

I did the best I could, got the old crud off and smeared some grease from my current part back on.

That's not dielectric grease? If not, what do I ask for at Radio shack?

I'm not sure about the name, but it's the same kind of heat sink compound that is smeared on a computer chip when it's mounted onto the motherboard of a computer. The saleperson, or manager at a good electronics or computer repair shop should know what you need. Good luck with Volvo. It's looking up man, just don't give up on it.

Andrew

They just call it heat sink paste, comes in a little tube, about $3.

Silicone thermal heat sink dielectric paste is what I have.
Dan

Excellent, thanks!

Thanks and I think you are right on with the power stage.

I checked the voltage on the #1 wire (negative) with it disconnected from the coil while key was in start position and only got 0.336V where I should have around 4V.

Back to the junkyard tomorrow, hopefully this does the trick.

Wait to see if fifty or so miles down the road the rough running comes back.

If you are disconnecting the battery when you install the coil, you are resetting the ecu to the default settings, and it takes some time for the brain to relearn faults. When the faults reappear the ecu tries to compensate and the problem pop up again.

Check engine light ? Codes?

Check your power stage (ignition amplifier) and the crank sensor.

I was about to start going through those tests in the manual.

The only check I see is for battery voltage, do you know of any others?

I found some very good info at: www.stepbystepvolvo.com. I'm not familiar with the type of ignition system your '89 uses, but the info Mr. Fred (author of this website and a book) gives can be applied to all 240, 740, or 940 Volvo systems.
Hope this helps,

Andrew

Thanks for the tip Andrew, great site.

It seems that the ignition amplifier is either broke or working, either has power or doesn't.

Since my car runs it seems that the ignition amplifier must be working however I'll check it over.

I'm going to check over everything in the ignition circuit.

However, the coil I got from the junkyard is still running great, 15 miles in.

My first thought is check the connections (especially inside the coil-end of the coil wire). I've bought wires with really shoddy copper ends that are standard, instead of the special ceramic/spring connectors I needed. Cheap wires, but not the right wires.


Other ideas:
Maybe it's a defective coil or there is a problem with the wiring. The power connections to the coil can develop corrosion inside the crimps, and if you have the 25-amp fuse under the hood, that can go bad too.

How does it run with the old cap/rotor/wires and new coil?

Good Luck!

Old cap was burned on the center electrode, it is unusable.

Old wires are junk too, #3 fell apart.

New wires are bougicord, coil is Bosch.

The fact that the coil worked good at first makes me wonder if my car ruined it because of some crossed wire or something.

I have had this same problem with several of my antique cars (1930 Model A, 1918 American LaFrance) after putting on a new coil. According to a friend of mine (that I buy most of my parts from) the problem is due to nearly ALL of the new coils being from China. If you got the coil from ANY of the main stream auto parts stores (including NAPA the coil is most likely from China. They don't look it, but coils are VERY difficult to make because of the hundreds of feet of tiny spooled wire. My friend suggested finding a NOS coil or EVEN a used one, as it would still be better than the garbage they sell now. I ended up buying NOS coils for both machines and it solved my problem.

So I went to the yard and pulled a crusty Bosch coil off a '93 for $25.

So far so good.

How the hell does Bosch get away with selling a junk coil for $85? They'll be hearing from me.

I would have been happy to pay twice that for one that works.

Any idea where to get a NOS coil?

Thanks for the help!

Well it's back to stumbling again.

Took about 15 miles this time.

Maybe the ignition amplifier?

Hi,

You could give Tasca a try. Made by Bosch but probably different than the new Bosch you have, around $45 from Tasca.

Travis

It's a Bosch, made in Brazil.

I'm a little reluctant to run right out and buy another.

Get a meter and check resistance. If the coil is shorted, as what you discribe, its no use anymore.

Basically inside there is wire wound in a coil protected by a plastic coating. It gets hot with the amps running thru it, it melts the coating of the wire and starts shorting out by arcing making your stuff run bad. Its usually intermittant.. Then it cools off and direct shorts one day and it wont start anymore.

Resistance in the secondary is slightly out of spec on both the old and new coils.

When I put the new one in it started running horribly within a mile or so.

Put the old one in and it runs smoother but still with the stumble/miss.

It seems like there's something else in the electrical system going on.

My cap was just burned on the center electrode but I don't know why, something in the distributor?

The other interesting thing is that there is a miss at low RPM's but if I put my foot on the floor it will rev up real nice and run just fine at high RPM.

How would an ignition/coil related issue improve with RPM?

The car has a miss or stumble with the old coil.

The new coil fixed the problem 100% for a short while, then it got even worse than it was with the old coil.

Spark plug wires and coil wires are not made very high quality anymore.. So maybe (if you have not already) check your coil wire while your at it..I have had wires fail with just the action of removing them and then re-installing them..They don't take much abuse today like they use to..Just a thought for you..

I'm not clear why you can't keep running old one?

If you can, get a third one from junkyard. or getting a new old-stock one from ebay is good idea.

How does it run with the AMM disconnected (not replaced, just disconnected)?
--
1980 245 Canadian B21A with SU carb but electronic ignition and M46 trans in Brampton, Ont.

With which coil installed?

Not at all elect related, but intake mani gasket?

It happens to have a brand new gasket.

go to you local gun shop

buy a .357 Mag Revolver.

Shoot that Volvo...it is mutant and needs to die for the sake of the rest of the 240 line. It is an embarassement.

God Save The Queen

I wouldn't be surprised if shooting it improved its condition, worst Volvo I've ever owned.