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Misfiring on cold start.

Koston740

New member
Joined
Nov 1, 2008
Location
York, PA
My 1992 Volvo 940 has been misfiring on cold starts for approximately one minute and when warmed up ... runs great!

Replaced: CAP and ROTOR, four plug wires, and four new spark plugs ... also new fuel pump and filter a year ago!
 
just because things are new doesn't mean there good, cold miss? fuel issue because the engines l lean maybe? dampness in the ignition system come to mind, how about the coil wire?
 
Crappy new secondary ignition parts is common!

Figure out which cylinder?

Can the coil make a nasty spark between the coil wire and ground? We're looking for it to jump 1/2" with loud Snap-snap-snap for sparks. Try holding onto it with your dangly bits too close to the fender for a memorable experience.
 
Watching. Mine does this as well..mine just did it first start after 2 days with newly installed wasted spark setup with new plugs/wires. Afr guage reads very rich and engine misses so bad you can't accelerate until the temp gauge starts to move..

Not trying to thread jack...

To clarify, mine has done this for some time, but changing to wasted spark crossed out coil/distributor
 
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Coolant temp sensor/wiring. Injectors partially clogged. Blown head gasket.

I would backprobe at the ecu/EZK connectors for proper resistance.

Do a cylinder drop test when it's acting up by unplugging injectors one area time and see if you can find which hole /s dead.

Blown HG can cause coolant to sleep in overnight and cause c9ld start misses.
 
I never thought headgasket....sounds right though.

I have replaced with new - plugs,wires, ECT and harness
I have replaced with "like new" -coil pack, injectors, fpr, knock sensor (and tried to tighten down lightly to make it less "aggressive"?) <---pretty sure I read that here
I have retapped and cleaned my injector grounds, cleaned grounds on fender
My brother and I made sure all gears were timed correctly.

Fuel pump replaced within the last year, as well as filter...same as OP

But...no smoke out exhaust, ever. Not even on cold starts. Would coolant being burned cause white smoke? Also MY engine was rebuilt 15k miles ago, I know that doesnt mean anything. But its better than 100k
 
I know, it's one that members here reminded me to look for. I blew the HG in my 1990 240 blowing out three or 4 cheap waterpumps nd getting a corroded head too hot. Pulled the head and had the pits welded back up and the head milled and it's been fine ever since. But yeah, it can be a very small HG leak with no smoke and cause a first start of day misfire. That's why I recommend cylinder drop test to see if it's just a certain cylinder.

We use scan tool data at the shop to identify which cylinder is missing. And injector test tools that activate the injectors and measure the fuel pressure drop to calculate the flow of each injector. I do injectors commonly on certain modern vehicles to fix cold start missesbut that's different than these old traktors. They are direct injection cars. Just an idea....the fuel demand is much higher on a cold start.

Another trick is to spritz water on the plug wires at night and look/listen for arcing.

I also have had the tips of new plugs unscrew themselves and cause cold start misses.
 
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Borrow a borescope from a buddy, pull your plugs and take a look. If you have a failed HG (which is pretty common, and will definitely cause cold/overnight misfires) one or more of the cylinders will be clean as a whistle. No carbon, or buildup.
 
Good to know and will definitely be look in the soon future.

All plugs look good

Plus, just started it this morning, blipped the throttle to make sure it was, indeed, running like ****. And unplugged the fuel injectors one by one and every one of them made the engine run 10x worse. So, not one specific cylinder?

I was supposed to find one injector that did NOT make the car run worse, correct?
 
Right... that's how load balance testing works.

Have you checked for exhaust gasses in the coolant? The test is non-invasive and the auto stores rent the kit. You just buy the testing fluid.
 
Sounds like a plan, ill get to it later today. Ill grab a borescope from my brother tomorrow hopefully.

And less than 15k, plus my brother and I installed a t cam and set the valve clearances about 9k ago
 
So, ive been lazy and havent been to the parts store to get that test kit...but I did look into the plug holes with a borescope and didn't see anything out of the ordinary?

I also installed an IPD turbo cam, so I set all of the valve clearances this morning to .015-.016. All my plugs were pregapped at .32 when I got them. Ive read some people experiences and they say to gap them to .28?

My brother has his gapped real small to try and remedy a misfire under load, like .22 or something, but he's running more fuel, higher boost..
 
Finally did something today, since i wasn't satisfied with the borescope confirming my head gasket being leak free, I rented the block tester kit.

<a href='http://i.imgur.com/oJpkUWg' title=''><img src='http://i.imgur.com/oJpkUWgl.jpg' alt='' title='Hosted by imgur.com' /></a>

All looks good, I pumped it for 5 minutes instead of the recommended 2 and no color change. I was worried lol

<a href='http://i.imgur.com/BZ7Q9Cp' title=''><img src='http://i.imgur.com/BZ7Q9Cpl.jpg' alt='' title='Hosted by imgur.com' /></a>
 
I have swapped it already with one from the jy, and it doesnt have a fuel smell out the vacuum line, but I know that doesnt mean anything. Ill try reading the pressure soon see what its looking like.
 
We have alkeyhol in our fuel. My turbo used to start like that and got worse when they added alcohol. My wagon started doing it over the last few years as they have added alcohol and no one actually regulates how much they really put in there. At least in jersey.

I rev my motor up till it clears and it's fine after that. Only on overnight cold starts pretty much is when this happens and my turbo is kjet with the wagon being LH2.4.

PS maybe try fuel from a different place? Didn't make any difference for me though.
 
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