Strange humidity related engine problem
 

I have been having a problem with my 3.2 engine when the relative humidity is very high- above 90%.

What usually happens is that the car will start but run very rough under 2000 rpm, sometimes stalling. It seems to be running very rich and will occasionally backfire a flame out the exhaust. If I can keep it running and get on the highway I can make the problem go away by running at 60-70 mph until the engine is warm and then accelerating hard up to redline. As I get up around 4-7k rpm the engine will miss pretty badly, but if I ease off slightly and then bring the revs back up it will work it's way through the rough spot and then everything is back to normal. The engine will idle and accelerate like normal with no missing.

I should mention that the car runs perfectly when the humidity is low and strangely enough the few times that I've been caught out in the rain, rain doesn't seem to cause the problem. I can usually tell when this problem is going to occur as soon as I get in the car by looking at the gauges...if the two left gauges are fogged I know that the humidity is high enough to cause the issue.

This morning I was going to go for an early drive, but the car wouldn't start. It cranks like crazy, but won't catch. Well, it did start and run for a minute, but died and won't restart and there is a strong gas odor.

Is almost as though the high barometric pressure is making the DME richen the mixture too much. :confused: I swapped DME relays with no positive result.

Has anyone that lives in a humid area had this problem?



edit for spelling

I don't know anyting about Motronic, but I did have a CIS car for about 15 years and dank air would set that thing off miserably. That's when they blow the airbox. So, me thinks it's the air density that is fooling the electronics. I wish I could tell you how to correct it. I should have put a bathroom heater in the engine bay for a few minutes prior to starting the CIS on those cold, dank mornings.

Whatever you end up doing due to the excellent advice here, I don't think running the car hard while cold to "clear it out" is the answer. Once things were set on the CIS, we just had to be patient on start up while getting things up to temp.

Jim,

Is the car a Targa or Cabrio?

This sounds like a serious moisture problem in the passenger compartment has gotten to the wiring harness or ECU connectors. My suggestion is to pull out that seat and be prepared to go through and pull apart every connector ... do the Q-tips & 9% vinegar, distilled water, compressed air dry, followed by 91% isopropyl alcohol cleaning treatment, followed by testing [when the gauges are fogged up] to be sure the problem is gone, then coat all of the connector pins with Dow Corning 4, 111, or 112 silicone grease.

Lol Milt, I was just out in the garage with a heat gun to see if i could dry it out enough to start. And I don't run it hard when cold...I let it get good and warm before "running it through" the stutter.

Warren, it is a coupe and the problem isn't that anything is actually wet so to speak. We just get some unbelievable humidity here, the kind where you can be sitting reading on a 78 degree day and you are drenched from sweating because there is so much moisture in the air. The car isn't musty or damp inside and I was just looking at the ECU connectors, which look good, but I will clean them off.

There is a cold front headed this way this afternoon and I think that will cure this episode, but I would like to find the cause of the problem. Is it possible that it might be a faulty sensor that is making the mixture too rich when the barometric pressure is high? It's been around 29.86in.

This problem is so bizarre that I almost hesitate to post about it, sort of like your crazy aunt that claims aliens living in the attic. :rolleyes: No, but seriously folks, this really does happen. In the interest of someone down the road who has a similar problem, I will continue to post until I get this figured out.

Late this afternoon a cold front came through and the humidity dropped a bit, so I went out and tried the car which wouldn't start all day. Sure enough it started. It was running rough and wanting to stall below 2k, but I drove about 20 min. and it cleared up and ran it's usual Swiss watch self. I don't get it, but I think that I'll get a dehumidifier for the garage until I figure it out so I can start the car on very humid days...how's that for a work around??:p

Jim:

Moisture can cause some ignition related issues with these cars and a thorough, methodical approach is required to solve these problems.

I'd suggest:

1) Inspect & replace distributor cap, rotor, and plug wires/connectors

2) If the DME relay is old, replace it.

3) Spray all of the engine sensor connectors with connectors cleaner/protectant such as Wurth electrical spray or the equivalent LubroMoly product. Both will remove oxidation and protect these connectors from moisture.

Steve,

1) I just replaced the cap and rotor last month, will do the wires next.
2) Replaced the DME relay yesterday.
3) I will clean the sensor connectors next.

Thanks all for the recommendations. Does anyone think that it's possible that the altitude sensor is faulty and that the barometric pressure changes are making it call for a richer mixture? Just a thought after observing how quickly this problem comes and goes according to atmospheric conditions.

My car (1985 3.2) acted similarly and I thought it was related to the humidity. Changing wires, distributer cap and rotor and plugs had no effect. I ran some Chevron Techron through the gas (1 bottle in 1/2 tank), and problem resolved. This has now happened twice in the three years that I've owned the car, both times the Techron cured it.

I'm guessing in my case it is a fouled injector that the Techron cleans, and the weather was just a red herring.

I don't know if it will help you, but it is inexpensive and worth a try.

I don't know about the altitude sensor, but my immediate thought after reading your initial post was "mixture."

Start up is a little rougher when it is really humid on my 86 3.2 but that clears up quickly.

When it's really hot and humid the car feels and acts like I do - lethargic,no misfires but not a lot of vigor either.

Possibly this climactic condition is at the margins for the Motronic system
parameters.

She runs the best during cool dry "football" weather.

With the exception of the above, my car runs just as well when it's very hot and humid as it does when it's very cold and dry.

I agree with Steve 100% since you already tried the "Italian Tune Up" which is nothing more than a lazymans ignition refresh.

Any luck Jim?

I'm experiencing similar symptoms that I also feel may be humidity related. Although my car will start and does not backfire, it does not have great throttle response and cold idle is extremely rough. However, in my case, the issue does not seem to go away once the car is warmed up. Here in MI it was 95+ degrees and high humidity earlier this week. It has cooled off some and the car runs much better again. Items recently replaced include:

- Spark plugs, wires, rotor, distributer cap
- O2 sensor
- Cylinder Head Temp sensor
- DME
- Fuel filter

Brian, mine is such a sporadic problem that it is hard to get a handle on it. I put a dehumidifier in the garage and the car has been starting and running fine, even with the very hot humid weather that we've had here this week. I cleaned off the sensor contacts, so I'll just have to wait and see if the problem resurfaces.

There is also a possibilty the moisture is affecting the air flow meter. You might try the adjustment to the potentiometer inside the
meter to give it more solid contact.

Same symptoms w/ mine the past coupe of weeks,
1. pulled the plugs and they all look good after she ran smooth.
2. after a good run, the engine compartment warms up and the stumble goes away. Maybe mixing things up in the fuel, drying out some moisture ???

I'm wondering if the new fuel additives in our gas is to blame, a friend was telling me that it's becoming a big problem in the marine industry. Has to do with loss of octane over a short period of time, dissolving varnishes in tanks clogging things up, and separation of fuel to water. Someone might have better information on the subject.

Like most commodities when the price is the highest the quality is the worst, supply and demand.
Bob

Did this problem start happening soon after you installed the new cap and rotor ? Its possible you have a defective part. Sounds to me you have a secondary ignition missfire. Your ignition system is most affected by humidity. I would also check the coil wire connection at the coil. The spark may be jumping to an easier ground than where it needs to go.
Maybe you can have a buddy watch for spark arcing (in the dark is sometimes easier) at one the times it wont start.

Kurt Williams

Jerry, I will add that to my list of things to check.

Bob, that's exactly what mine was doing....after it warmed up the stumble disappeared.

Kurt, it did it before and after I changed plugs/cap/rotor. The coil wire seems firmly connected on both ends and there is no arcing visible in the dark.

As I mentioned before, putting a dehumidifier in the garage seems to have stopped the problem. And it was only when the relative humidty went above 90% that i ever had the stumble till it warmed up. Driving in the rain had no ill affect on the car.

911 starting problem when humid
 

I have the same problem. No start or hard to start when humid. If it does eventually start it will run ruff for a few miles but then begins to run normally. When air is dry starts right up evry time..

Was a resolution for this problem?

Hmmm 10 year old thread .....

I had a similar problem and it was a cracked 1 year old dizzy cap.