1997 850T warm weather / fuel problems

telemako · Post by **telemako** » 12 Apr 2015, 14:23

Hi all,
I've been reading posts here for the last two years hoping to find something to explain the persistent problem(s) I've been having with a much-beloved '97 850T. I've found a few things that might be related, but nothing that exactly fits.

I'm the third owner of this car, & bought it 4 years ago. It has 170,000 miles on it.

The problem (in its current manifestation) is like this. If it's cold out (and I mean the weather, not the engine temp), the car starts great for the most part. Catches, revs up, idles smoothly. But if I (say) park it in the evening and wait till the afternoon of the following day, when it's been sitting in the sun (and warming up), it will start very poorly: it catches, then sounds like it's choking, can't get its RPMs up (or the RPM dial is all over the place), and will often die if not given gas. I can get it to steady out by giving it some gas. (The exhaust is somewhat thick/smoky if I do.) It also will behave this way -- and this is either totally unrelated or perhaps a significant clue -- will do something very similar, 1 in (say) 5 times, the first time I start it up after adding gas to the tank. Both in cases of (ambient) warmth and adding gas, it only does this the first time it starts in a while: e.g. if I can get it started, it will be fine for the rest of the day. So I've been starting it every morning, when it's cool out, and it'll be fine till the next day. My mechanic was really skeptical that it had anything to do with the weather (not the engine temp), understandably, but I'm quite sure. It has no trouble starting up in warm weather once it's done so once for the day -- it seems to be the temperature change that gives it trouble. If I let it "bake" in the sun, it will almost certainly start poorly. In conjunction with this, it will occasionally die while idling if it's been starting poorly. (This happened yesterday, in the middle of some errands. Had started poorly, then did fine at the next few stops and restarts, then suddenly died while switching from R to D in a parking lot.) I figured it was time to look into it again, since (from past experience) it starts acting up more and more till it dies and I have to tow it to the shop.

The first time it started "acting up" like this it eventually stopped starting at all. Mechanics diagnosed it as a totally clogged/junked MAF sensor. Replacing that fixed the problem temporarily. Started acting up again, died again, this time (maybe 9 months later) replaced the fuel pump. It sat (getting hot in the sun, I might add!) in the mechanic's lot, then, when I went to pick it up, started and died immediately on trying it. They couldn't figure it out, but suggested it might be a leak in a fuel line close to (but not) in the pump, somewhere inaccessible. Got it going after a few attempts, has been more or less fine since, with occasional trouble when adding gas, and now has started having trouble again. I'm pretty sure within about a week it will die again, and I'll have to have it towed.

My uneducated sense is that the MAF problems (and fouled spark plugs, another thing we replaced along the way) are a symptom of a deeper problem. And because the trouble when adding gas and the trouble when it's been sitting in the sun are so similar, my guess is that these things are related -- but who knows.

Replaced the battery in January.

Apologies for the involved narrative -- not sure what might be important. I don't know much about auto work myself but I would be supremely grateful for any suggestions to pass along or check myself, and happy to clarify / report back on any lines of inquiry.

thanks kindly..

Post by **Ozark Lee** » 12 Apr 2015, 14:57

Is the Check Engine light on? Do you have any P codes?

If you do get the codes read post back the code numbers. The auto parts stores tend to give you a code description that may or may not be accurate. With the actual Pxxxx code number we can make better sense of things to help you.

The start and die aspect of things make me suspect a fuel pump relay problem and the fuel pump relay often is ambient temperature sensitive as it begins to fail. A bad fuel pump relay won't typically set a P code.

...Lee

telemako · Post by **telemako** » 12 Apr 2015, 15:08

No Check Engine light. I'll try to get the codes. Any idea if a bad f.pump relay would explain its trouble after adding gas to the tank, too?

Thanks, Lee.

Post by **Ozark Lee** » 12 Apr 2015, 16:01

The relay wouldn't cause an after fueling problem but overfilling the tank can. When you fill the car just let the pump run until it clicks off and don't try to round to the next dollar or some other even amount. If it clicks off at $28.37 just leave it there. I have had problems with overfilling and I am guessing that I wound up getting raw fuel into the charcoal canister and then the raw fuel gets sucked into the intake when the purge valve opens. So long as I don't overfill it hasn't been a problem since.

You can try to just bypass the fuel pump relay for testing purposes and see if things change. Remove relay 103 and install a wire between the socket positions associated with pins 15 and 87. The are the "north - south" pins that are perpendicular to each other. The numbers are molded into the socket but they can be tough to see.

...Lee

telemako · Post by **telemako** » 12 Apr 2015, 17:15

Definitely hasn't been overfilled (especially since getting the new fuel pump in it, I've been careful not to, and have always just stopped at the Click). I'll talk to my mechanic about trying to bypass. I think it might be tricky to show that it's definitely the fuel relay by bypassing it since it will often start just fine, but I'll give it a shot. Any other ideas for when I take it in? I really appreciate your help, Lee.

telemako · Post by **telemako** » 12 Apr 2015, 17:17

Is it reasonable for me to think that having to give it a bunch of gas to get it going is part of what fouled/fouls the MAF sensor?

Post by **Ozark Lee** » 12 Apr 2015, 18:01

The MAF is well before the place where any fuel is introduced into the system, it is the first thing after the air filter so fuel related things won't contaminate it. I have seen the MAF get fouled with a K&N air filter after it gets cleaned and oiled or they can just get dirty. If you ever decide to clean th MAF sensor use electrical contact cleaner or MAF cleaner only and just spray it on and let it dry. Don't scrub the MAF or even touch it. You may want to go as far as wearing sunglasses so that you don't even look at it too hard - it is that touchy.

The MAF on this engine is incredibly picky and I have had trouble with using aftermarket brand or rebuilt MAF sensors. As brutally painful as it is price wise that is one of those parts that should be OEM Bosch only. If the MAF wasn't replaced with a new OEM original that might be the root of your problem.

Have you unplugged the MAF and driven without it? If the idle smooths out and the car generally runs better with it unplugged that is an indication that it is indeed bad. The throttle response will be weird and the mileage is terrible but that is a valid test for MAF issues.

...Lee