Diagnosing time...

[Quantumleap]

Hey everybody! Was driving home today and my '89 was sputtering...at first I thought it was the auto tranny slipping, but found that she was doing it in neutral, and at stop lights. Power is slightly down but when coasting along and not pushing too much on the gas, a pronounced sputter is making itself known, car's been running really good lately, has 200k well cared for miles.

When she "sputters", the fuel economy gauge in the instrument cluster bounces, which tells me this is a fuel delivery issue, could it be just clogged injectors, fuel filter or *gasp* fuel pump? If anyone else has experienced this or has a suggestion, it would be greatly appreciated. Cheers!

[86GT635]

I was wondering if maybe the relays are going wonky. You have 3 by the battery I think on the 88/89, if it's like the earlier 85: One for O2 sensor, one for the fuel pump, and the other is the main relay.

[ShapeShifter]

On '88 and '89, there are only two relays. Main and fuel.

[Quantumleap]

Wow never thought of the relays, I'll just replace both of them, then fill up tank with gas and add injector cleaner, and replace fuel filter over the long weekend. Regarding those relays, esp the fuel pump one, has this happened before, causing one to think it was something else?

[RSheiman]

I just experienced something similar with my M6. For a few bucks, I replaced the fuel pump relay and it seems to have resolved. My 86 635 has this attached to the fuse box, my 88 M6 has this behind the glove compartment, both 4 prong . If the latter, don't forget to clear the straps that support the glove box door before putting the panel back, sounds simple but you think I would have learned by now.

[Quantumleap]

You know what, I've had a suspicion that the problem is electrical, because of the intermittent nature of the issue and the car runs good and strong when it isn't "sputtering"...will definitely start with the relay. Thanks for the suggestions!

[CW6er]

Here is a listing of the Relay numbers and sources:
http://bigcoupe.com/phpBB2/viewtopic.php?t=16409

The other thing to check are the plugs for the CTS (Coolant TEmp Sensor), and the Speed and Ref. Senors. The get old and brittle with age and can get intermittent.

[Quantumleap]

Would the CTS, Speed and (what's a "ref sensors") getting old cause the car to sputter occasionally? Speedo works fine, as does my temp gauge. When the engine sputters, the fuel economy gauge bounces and check engine light flickers, then everything goes back to normal, (Happening more now). Replaced fuel pump relay and main relay, no change in condition, where to check next? Thanks for the replies!

[CW6er]

Yes, the engine will run like it is possessed if the CTS plug is bad or making intermittent contact. I had a pin in the CTS plug get pushed back and finally became intermittent and the car started bucking and snorting and finally died and refused to start. I used a paper clip to push the pin back into the plug from the back and held it as I plugged it back in. I haven't had a problem since (but I did buy a new plug with a pigtail for the glovebox just in case. You can get them at a local auto supply).

CTS Test Values:
Coolant
Temp .......... Ohms
14ºF = ... 8200 - 10500
68ºF = ... 2200 - 2700
176ºF = ... 300 - 360
___

The Speed and Reference Sensors are on the rear brace that runs between the intake manifold and the engine and go to the ECU for fueling and spark control.

Checking the Speed and Reference Sensors:


Check the plugs to the sensors first, the plastic can get brittle with age and they can crack around the wire locking bail leaving them loose. Then check their resistance as below (won't hurt to check them both hot and cold if the car's hard starting is temperature sensitive):



http://bigcoupe.com/ims/pic.php?u=21GvpX2&i=349

[ShapeShifter]

There is are not a reference sensor on the B35.

Have you done a stomp test to get the fault code??

[Quantumleap]

Wow, I'll have a look at the CTS next, since this very same sensor gave me check engine lights in my '01 VW Cabrio, and Eurovan, causing them run a little rough, replacing them fixed the problem...looks like it does quite a number on our 6'ers as well...thanks CW! And Shapeshifter, I haven't done the stomp test yet, will need a refresher on how to do that lol, or I can get it read for free around here locally, and get a printout of the fault codes that pop up, if any

[ShapeShifter]

Just turn the key before engine start (all cluster lights on) push the gas pedal to the floor 5 times rather quickly. Be sure to hit the switch under the pedal.

Count the check engine flashes.

[Quantumleap]

The baby blue one on the right? (Found the pic you posted a while ago, CW, hope you don't mind). And Porschedude, when I look at the CE flashes, how many flashes am I looking for?
414056

[ldk]

For the 'stomp test,' go to youtube and search for 'BMW stomp test.' You'll see many examples, and by viewing those you'll see how to read the code or codes you have.

[OldGringo]

MAF might be an easy solution too. Take it off, check the contacts for the plug, if they look nasty clean them with an emery board or very fine sandpaper folded on a screwdriver blade. Then use a spray can of MAF cleaner, Nothing Else, to clean the inside sensor portion. This is inside the air flap/door, spray-do not touch. Put it back together. Check for results. Cost about six bucks for the cleaner, but you woun't need to use all of it.