Beverly has the swine flu

Okay, I don't know if cars can get the swine flu, but since I wanted attention, I thought I'd pull a media trick and put it in my headline.

Anyway, my gas milage went from 18.8 or so (with quick sprint driving two and from school) to 13.0 while trying to use as little gas as possible. Anyone present in my garage when I fire my car up knows that they probably shouldn't light a match because the place would explode.

Last weekend I decided it was time to give Bev some love.
Note that Bev just got $350 worth of love 3 weeks ago with a new cap and rotor, new air filter, new set of bosch spark plugs, among lots of front end suspension work (that didn't actually include the suspension).

This didn't keep me from giving a little bit more love...
I checked all the spark plug gaps, checked resistance on all wires (which I know doesn't mean they are perfectly okay, but it was a nice start), checked the resistance on the coolent temp sensor, air flow meter, and checked the fault codes(there were none). Everything checked out.
Put it all back together, and she fired up and ran beautifully. I laughed.

48 hours later she's back to consuming gas like a chevy suburban
I suspect a wiring problem.
I should be able to test most of my sensors from the main computer connection in the glove box, right? This should test both the sensors as well as the wires that go to them? I'll keep everyone up to date. Suggestions are welcome, but not required yet.
It's slow enough around here I'm willing to detail a little work, in order to add to the collective hive mind of information that is BENN



Edited 1 time(s). Last edit at 05/18/2009 04:33PM by daniel.

Oh yeah, I do actually have a question.
Is there any reason that my computer wouldn't throw a fault code when the car is running rich enough to light the tail pipe on fire? Shouldn't the CO2 sensor be complaining to the ECU?

i am not an expert in troubleshooting the technical/mechanical aspects of e30s, but i think the ECU is the last place you should look. It could be a faulty o2 sensor, but as you said, it should throw a code. my check engine light came on in the fall and it turned out to be the o2 sensor. i never replaced it, and since that one day the check engine light has never come on.

I would dare say that you need a new O2 sensor. The computer will make the car run rich on purpose if it is getting bad readings from the O2 sensor as a rich condition is better than a lean one. Try disconnecting the sensor and run it like that and see if your mpg changes. If it doesn't then that is the problem.

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Earendil
Okay, I don't know if cars can get the swine flu, but since I wanted attention, I thought I'd pull a media trick and put it in my headline.

Anyway, my gas milage went from 18.8 or so (with quick sprint driving two and from school) to 13.0 while trying to use as little gas as possible. Anyone present in my garage when I fire my car up knows that they probably shouldn't light a match because the place would explode.

Last weekend I decided it was time to give Bev some love.
Note that Bev just got $350 worth of love 3 weeks ago with a new cap and rotor, new air filter, new set of bosch spark plugs, among lots of front end suspension work (that didn't actually include the suspension).

This didn't keep me from giving a little bit more love...
I checked all the spark plug gaps, checked resistance on all wires (which I know doesn't mean they are perfectly okay, but it was a nice start), checked the resistance on the coolent temp sensor, air flow meter, and checked the fault codes(there were none). Everything checked out.
Put it all back together, and she fired up and ran beautifully. I laughed.

48 hours later she's back to consuming gas like a chevy suburban
I suspect a wiring problem.
I should be able to test most of my sensors from the main computer connection in the glove box, right? This should test both the sensors as well as the wires that go to them? I'll keep everyone up to date. Suggestions are welcome, but not required yet.
It's slow enough around here I'm willing to detail a little work, in order to add to the collective hive mind of information that is BENN

First off, what year and model is it?

You say you smell gas, is it the raw gas smell you get with a leak? Is it just on cold start you smell it or all the time, is it hard starting when hot and does a plume of black smoke come out when it starts (hot start)??? Got a name, I'm new here.

Rick

The name is Tyler, and I drive an '89 325i with an unmodded M20 motor (stick too, if anyone cares).

I wasn't trying to suggest that it was my ECU that was bad, just reasons why the ECU wouldn't report a fault.

I didn't suspect my O2 sensor, as I just replaced that in the fall. But it's worth checking out.

The tail pipe, cold engine or hot, smells of raw unburnt gas. Not quite as bad as if an entire cylinder wasn't firing, but pretty bad.
No black smoke. The car takes a couple turns to fire up cold or hot, but no more than it always has. Runs bad one way or the other.

I notice it in the power (especially when the curve kicks in around 3000), and at that point I also notice a rough feeling. Not real rough, but the car doesn't scream "MORE!" at me, but instead sounds like a lot of other engines wimping "please...no..."



Edited 1 time(s). Last edit at 05/15/2009 12:21PM by Earendil.

Hey Tyler, that sheds a little more light on the subject. First thing you need to do is a compression test, if you get a low cylinder (on every low one) put a few teaspoons of oil and run another test on that cylinder.

Once we get the basics in tow then we can figure it out, don't keep throwing parts at it, lets try get to the heart of the matter.

Rick

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rkj
Hey Tyler, that sheds a little more light on the subject. First thing you need to do is a compression test, if you get a low cylinder (on every low one) put a few teaspoons of oil and run another test on that cylinder.

Once we get the basics in tow then we can figure it out, don't keep throwing parts at it, lets try get to the heart of the matter.

Rick

I can't possibly keep throwing parts at the problem, as I haven't started throwing parts at it ;-)

All the work I did was spring time tune up, for which the car ran fine before and after.
It might be good to do a compression test, as I haven't done one in almost 2 years. However my problem started, went away, and then started again.
It ran so well that I took her out for a 2am "cruise" with a 325i E36. Both cars "cruised" at about the same speed.

I suspect the wiring to my fuel pump as well. I know that I had an issue in the past with the ground wire failing. The pump still runs, because the pump its self is slightly ground, however the resistance to ground goes way up, and so the current drops way off, causing the pump to work but giving a lower fuel pressure.

I still think with a problem that comes and goes that wiring or sensors are a likely suspect. Mechanical pieces, when they fail, tend to stay failed in my experience :-)

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Earendil
The tail pipe, cold engine or hot, smells of raw unburnt gas.

so does my car. i hope it goes away once i replace the o2 sensor.

I had a car that suddenly started getting crappy gas mileage and I could smell fuel too. I found the problem was the fuel line connection where the hard fuel line goes to a rubber one in the rear of the engine bay. The clamp had worked its way loose and fuel was pouring out. Talk about bad gas mileage!

What woodcutter had to say - I would suspect a fuel leak on the pressure side of the fuel system. Doesn,t show when the engine isn't running, but leaks in a spot that doesn,t show when running. That would explain the varying fuel consumption. Things like compression etc. would show up as consistent excess fuel consunption and smoke.

salut, Bob p.

A fuel leak is a good idea, but I think I can rule it out. I'm measuring my drop in MPG with the 13 btn OBC. The OBC should not measure gas leaking, as I think it tabulates MPG with the injectors, correct?

Unless of course the fuel leak was so bad that the pressure had actually dropped, but I think I'd see a leak that big ;-)

I go under the hood more tomorrow, but I did find out a few more things driving around.
It was 86 degrees here yesterday, and my car was running LEAN. Since the nights are still 40 degrees, and the daytime temp has been around 50-60 for the previous few weeks, what are the chances that it's the air intake temp sensor? The M20 did have one of those, right? Embedded some place in the AFM?

...google searching later...

I actually am doubting we have one now, as I can't find any information on how to test it, either online or in my bentley...
How can we not have an air temp sensor?!

I also unplugged the O2 sensor the other day. Car ran like complete shit instead of semi-shit. I think I can go looking other places for the time being, leaving the O2 sensor on the back burner for now.

So what you are saying is that the 'indicated' mpg is poor. Is the actual or real mpg poor? I never use the computer to keep tabs on mileage, but use the old 'how many miles (kilometres) do I get for X gallons (litres) of fuel' method. Check that. If it is quite different than your computer figure (i.e. much higher) then you just have an instrument error and need not worry.

salut, Bob p.

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Bob P 325is 88
So what you are saying is that the 'indicated' mpg is poor. Is the actual or real mpg poor? I never use the computer to keep tabs on mileage, but use the old 'how many miles (kilometres) do I get for X gallons (litres) of fuel' method. Check that. If it is quite different than your computer figure (i.e. much higher) then you just have an instrument error and need not worry.

salut, Bob p.

All but for the little part about how I can feel the engine running rougher, with less power, and only then if I check my trip MPG do I see a significant drop. When I hooped in the car in the between stages, when she was running well, I checked the MPG again and found that she was back up to par.

Interestingly, when she was running lean yesterday, the MPG was good. Makes sense I suppose. I may not have full power, but at least I'm burning all the fuel I put in the cylinders :-)

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Earendil

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Bob P 325is 88
So what you are saying is that the 'indicated' mpg is poor. Is the actual or real mpg poor? I never use the computer to keep tabs on mileage, but use the old 'how many miles (kilometres) do I get for X gallons (litres) of fuel' method. Check that. If it is quite different than your computer figure (i.e. much higher) then you just have an instrument error and need not worry.

salut, Bob p.

All but for the little part about how I can feel the engine running rougher, with less power, and only then if I check my trip MPG do I see a significant drop. When I hooped in the car in the between stages, when she was running well, I checked the MPG again and found that she was back up to par.

Interestingly, when she was running lean yesterday, the MPG was good. Makes sense I suppose. I may not have full power, but at least I'm burning all the fuel I put in the cylinders :-)

So do a fuel pressure test, both idling and running on the road. Then I do an overnight leak down test to see how pressure it holds overnight.

Rick

So Bev got some love today.

I checked the fuel pressure, which while running was at 40psi, just within the Bentley spec (40-46). Pulling the feed back line to the regulator produced 48psi, so that's about spot on. Of course, I don't know how accurate my $20 gauge.

I checked out the voltage at the fuel pump, that was spot on. I don't have a multimeter capable of going up to the specified 7 amps, so that'll have to wait.

Found out my TPS is off. Doesn't register idle location, and kicks into "Full Throttle" a tiny bit early. This isn't causing my problem though.

Hot wired my multimeter into my air flow meter, and watched the gauge function pretty linearly as I accelerated.

In the end, I found nothing really off, so I put her all back together, and took her out to make sure I hadn't busted anything, before I really need her this evening.
She drove like a race car again. Pulls right through 3000rpm without any roughness at all, infact I swear around 4000rpm I could hear the car laughing. I certainly was. It was 67degrees, which kind of blows my air temp sensor theory.

So, I'm stumped. Perhaps it's just as the Beatles say, "All we need is love".
Until next rough engine...

Maybe you need to put some fuel injector cleaner in the fuel tank and call it good. That is always a dose of medicine that can never hurt and highly recommended!

Tyler, does this running condition show itself on wet days or is there any weather condition that affects it? Rick

My poor mileage problem a couple of years ago was due to injectors being dirty. Had them cleaned and stopped using the ARCO gas. That helped. A dose of injector cleaner every couple of months since. Like you, I went through a lot of parts before landing on the injectors. It cost about $100 to have them cleaned. I did the exchange in and out myself so saved some on that.

Bob in Everett

Update: I'm still getting good gas millage, without cause. I don't know what was wrong, but for now, it's working great.

Oh, and again, because somehow this impression was given, I have spent *no* money fixing this particular problem. I have replaced broken parts for other reasons (mostly becuase they were broken ) in the past 12 months, and those were listed. I haven't bought anything for this particular problem yet. And, as it stands, I won't be.

For the record, On the long desert drive back home, I was averaging 23mpg at 70mph. Not bad for a 20 y.o. car if I do say so myself

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Earendil
Update: I'm still getting good gas millage, without cause. I don't know what was wrong, but for now, it's working great.
<snip>
For the record, On the long desert drive back home, I was averaging 23mpg at 70mph. Not bad for a 20 y.o. car if I do say so myself

That doesn't look all that good to me. I get 29 mpg at 70 to 80 mph. Of course, I have an eta, maybe you have one of those high powered i cars and that's all you can get.

John

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John Yust

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Earendil
Update: I'm still getting good gas millage, without cause. I don't know what was wrong, but for now, it's working great.
<snip>
For the record, On the long desert drive back home, I was averaging 23mpg at 70mph. Not bad for a 20 y.o. car if I do say so myself

That doesn't look all that good to me. I get 29 mpg at 70 to 80 mph. Of course, I have an eta, maybe you have one of those high powered i cars and that's all you can get.

John

Yes, I do. 325i rated by BMW to get 18 city and 23 hwy.
The "bad" gas mileage it was getting before was 14-16mpg
So 23mpg is a good thing

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Earendil
I actually am doubting we have one now, as I can't find any information on how to test it, either online or in my bentley...
How can we not have an air temp sensor?!
.

I believe it is on the outside of the air filter box. Its got an oval shape on the top of it.

Jack