Misfiring on Startup

[socalfiver]

Got a problem with my '80 Automatic.

It has a steady misfire when first started. It runs on 5 cylinders with very low power. It doesn't run on all 6 until I floor it and get the revs up.

What gives? After the "flooring", it runs nice and smooth on all 6. Any ideas?


I've put about 950 miles on it in the past 2 weeks. It had been sitting for a while before that.

It blows a wisp of smoke out the tailpipe when started from cold.[/i]

[Blaise]

I am going out on a limb here and am definitely no expert. But, this sure sounds like the symptoms of a vacuum leak.

The same issue happened to me, upon reassembly of my intake. I had a vacuum line hooked up wrong.

But it sounds like you have not messed with your car. So, I would check for cracked vacuum lines and the like.

[socalfiver]

On the contrary, I have worked on it quite a bit to get it up and running. Disassembled the intake to replace fuel rail hose, had the valve cover off to adjust the valves, had the radiator out to change the fan clutch' clean and adjust the throttle body and afm... I feel like I've taken it apart almost every day since I got it.

I will investigate vacuum leaks, thanks for the lead. Now that you mention it, I think the breather hose on the valve cover may have a crack in it.


I usually use starting fluid to check for vac leaks.

I have to get her running smooth so I can get smogged.

[Lenny D.]

Pull your plugs and clean (or replace) them. You have oil slipping past the oil ring on startup and a plug is fouling and you also possibly have carbon buildup on the electrode from the car sitting.

[socalfiver]

Is it possible that it's worn valve guide seals allowing oil into the cylinder from above? I'd love to get away with just a head r&r instead of dealing with block problems.

Oil slipping past the oil ring... is there any way to fix that besides a ring job?

I put new bosch silber plugs in when I got it. Will pull and clean plugs and see how that goes.

I've just put my '66 Thunderbird up for sale to fund engine repairs on this car.

[Blaise]

Did it idle properly before you did all of this work?

[Mike W.]

It could also have a cracked head or blown head gasket. Does it use any coolant? I've had where I only had to top off every month or 6 weeks, but a cracked head was allowing just enough water in to cause it to run on 5 for the first quarter mile or so in the AM.

[socalfiver]

It's intermittant. This morning, it started and ran perfect on all 6, and I have done nothing to it. Vac hoses are all in good shape and routed correctly, but valve cover breather hose is cracked. Awaiting replacement from bmw.

Occasionally it runs perfect, but mostly runs on 5 for the first few miles.

[Lenny D.]

Then I say you have a too lean condition at startup, another issue altogether. And yes, only a ring job will solve oil slipping past the oil ring but I forgot about the valve guides, and yes again, they are the most likely suspect for a puff of smoke on cold startup.

Rereading your last post, if you have one cylinder that is constantly not/misfiring it will be easy to find it. When the condition is present, pull (carefully) the HT leads to the plugs one at a time to find the one that doesn't make any difference. Pull that plug and look at it. Carbon will be connecting the electrode to the insulator nose - see here. Other plug issues are addressed as well.

I suspect if you are having oil slip past from the guide you are building up a slight amount of oil on the plug that misfires until it burns off. The plug will tell you that upon inspection.

Then, again, Mike could be correct, but inspecting the plugs will tell a lot.

[socalfiver]

Am I wrong in assuming that a dead cylinder will lead to a lean condition when the oxygen sensor detects the unburned air/fuel mixture?

Fuel Injection is (relatively) new to me. My cars for the past 15 years have all been carbed. I had another 528I, but it never gave me any FI problems, so I never had to learn it before.

I'll check the plugs when the car cools. Problem is, I drive it all the time so it never cools!

[pmaronoff]

I also have an 80 auto that does sort of the same thing. Mine starts fine. If I disconnect the 02 during this warmup period idle is slightly better. I have replaced all the temp sensors. Tried different AFMs and John Savage was nice enough to send me a ECU to try. Nothing helps. All grounds are good and checking continuity from the temp sensor plugs to the ECU connector are all good too. I do have the bad valve guide issue sucking oil into the cylinders. Maybe that is the common cause. Has anyone replaced the valve guides and still has this lean boggy warm up problem? Sorry for the verbose but trying to keep your car from stalling with an auto trans can be vexing.

[socalfiver]

Found a head today at the boneyard. I will replace seals and install and see if that helps.

[GripGreg]

You may as well get the valves re-ground too. Make it a complete re-build since it's off the car. Don't think thrifty since it's already in your lao. Have it pressure tested at the same time, looking for leaks? Good Luck,,,,Greg

[socalfiver]

Head rebuilt and replaced, misfire remained. Because it pressure tested good, I did not opt for the valve job. They wanted an additional $265.

Turned out to be the #6 injector plug. It works itself loose. Or rather, it did until I replaced it.

I figured out that when it was running rough, holding a screwdriver on the #6 injector made it smooth out, even though the plug appeared to be seated. I replaced all of the injector connectors with nicer, beefier connectors from a boneyard 325e. The rubber boots were much nicer than my originals, as well. It can be a PITA to get the old wire terminals out, but it saves you about $26 ea over buying new plugs and boots from the dealer.

It's now running on all 6 all the time.