Weird Things Re Happening! Help!

[PhoenixOp]

'85 635CSi: Starts great, idles great, when you start to drive, runs great, then randomly and for no reason it will act like it has no power. It's like you give it a little throttle and it loses power. If you ease off the throttle it idles and runs fine. Then if ypu get on the throttle hard, she''ll run like a wild woman, fast and mean.

It's on and off. For the next few minutes, it's smooth as silk, than WHAM, it starts acting crazy again. It acts like some kind of fuel starvation. I just bought it, so still has whatever gas was in it.

Bad fuel? Bad/dirty injectors? Fuel filter partial blockage? Random open wire to fuel pump(s)? These cars are so different, that I'm grabbing at straws. On my '67 Buick, it would be simple, accelrator pump in the carburetor.

I miss simple, but I really love these friggin' cars...

Thanks ahead,
Mike

[Pod]

Well, do those things you mentioned and see if that does the trick. With a new car it doesn't hurt to give it a good going over anyway

[PhoenixOp]

Thanks Pod, I'll give it a shot.

I was just wondering if there was something specific to these cars.

Thanks again,

Mike

[Pod]

I bought a S1 car once that just would not run properly. In the end, after changing the filter, external pump; checking the FPRV etc etc I found that the rubber pipe from the tank to the pump was clogged with rust and volume would not flow. If these cars sit for a long time, that can easily happen.

I think its likely that you have an in-tank pump as well as an external one (Euro cars often have just the ext. pump). So check the filter screen as well.

Its often the last (but simplest) thing you look at

BTW, drain all the old fuel and make sure the tank is clean (inside).

If you blow out the return line with compressed air, make sure you remove the filler cap first!!!

At least if you do all these chores you'll know what it isn't if that does not do the trick.

Good luck!

[PhoenixOp]

This thing was driven occasionally over the last 5 years. Was in a garage though. The weird thing was, I drove it yesterday and it ran beautifully.

Maybe it didn't want to go to the DMV to get registered. That's where I was going. Yesterday was just a test drive, today was work.

Moody?

Thanks again,
Mike

[sharkfan]

I had something similar with my 635CSi that was laid up for a slightly longer length of time - I chased around plugs, filters, distributor cap, rotor arm and fuel pump before finally finding the cause - a blocked suction strainer inside the fuel tank.

It was all waxy and after pre-ordering the gasket it took about 20 minutes to get the strainer out, clean it with an old toothbrush and clean petrol and replace it.

Job done, no issues since.

[PhoenixOp]

I'm going to work from the back forward. Seems like the most logical and least expensive. So off to the tank I go...

Thanks for the insight Sharkfan,

Mike

[Ralph in Socal]

Best place to start and clean the system all the way up to the injectors. Replace all the hoses as well and don't forget the Cold Start Valve fuel hose. 8 mm fuel injection hose (6 feet to make sure you have enough) for the most part except the tank to external pump which is 12 mm (2 feet of this hose). A bit of a PITA to do the tank hoses but a necessity as a leak in the large feed hose will cause the pump to cavitate and lose pressure.

Bad fuel will also give you the symptoms described. Good luck.

Ralph

[PhoenixOp]

Thanks Ralph,

Mike

[Chris Wright]

'85 635CSi: Starts great, idles great, when you start to drive, runs great, then randomly and for no reason it will act like it has no power. It's like you give it a little throttle and it loses power. If you ease off the throttle it idles and runs fine. Then if ypu get on the throttle hard, she''ll run like a wild woman, fast and mean.

These cars are so different, that I'm grabbing at straws. On my '67 Buick, it would be simple, accelrator pump in the carburetor.

I miss simple, but I really love these friggin' cars...

Thanks ahead,
Mike

First things first; have you seen the Goodies page yet? Check it out for links to free online workshop manuals, parts catalogs, wiring diagrams, etc. Your best friend will be the Bentley Manual mentioned on the page:

viewtopic.php?t=10410

_____________________________

If you want to troubleshoot the problem before throwing time and parts at it, the first think to check is the throttle position switch. It tells the computer (ECM) when the throttle is opened so it can start to control the idle/fueling at low RPM.

You mentioned the accelerator pump. The injection system has one – Sort of.

When you open the throttle the vacuum drops in the top of the FPR (Fuel Pressure Regulator) and the fuel pressure rises to enrichen the mixture (see below). At the same time the increased air flow through the AFM (Air Flow Meter) causes the AFM flapper door to initially over-swing to a rich mixture until the air flow steadies.

At small throttle openings, a sticky AFM would not give the correct flow to the computer (ECM).

If you want to troubleshoot the fuel system, you need make (or get) a fuel pressure gauge to see if the pressure is down when the power is down. Here is a link to making the gauge setup below:

viewtopic.php?t=23178&
(don’t get the Harbor freight one before reading all of the comments about them breaking right out of the box)



With the engine off, jump the fuel pump relay and the fuel pressure should be 43.5 +/-0.9 psi (3.0 bar)

If the pressure is too low, slowly squeeze off the fuel return line out of the bottom of the Fuel Pressure Regulator (FPR) and see if the pressure comes up. If it does, the FPR is bad, if not, the pump may be bad, check the fuel pump delivery rate.

With the engine running, normal range is 40.6 to 46.4psi at idle.

Removed the vacuum hose from the top the FPR, fuel pressure should increase, when reattached, it should return to its previous pressure.

The next test is fuel delivery (volume). Use a small length of hose on the bottom of the FPR outlet into a measuring cup:

At least 1.9 Qts (1.8L) in exactly one minute from the bottom of the FPR with the fuel pump jumped.

(All of this stuff is in the Bentley)

[PhoenixOp]

Hey Chris:
Thank you for the info on the fuel system, but before I tackle that I have to get past some other stupid stuff. As follows.
First, yesterday i decided to try the "Seafoam" treatment that is used on 850's. The gas gauge "looked" like it had about 1/8 to 1/4 of a tank. Not being familiar with e24's, I figured the little red light by the "R" was lying or there was one really big reserve in this thing. So I promptly hopped in and took off for the gas station, which, is 5 miles away. At about the 2 mile mark, it started to act weird again, right up until it ran out of gas. Got it home, put some gas in and it ran great. Put non-ethanol premium in it. Runs great, just a little rough. Probably needs a tune-up. Wait, there's more.

Today i got in it, ran some errands then on the way home it started the "weird" again. It died coming in the driveway. Battery was dead. Apparently the alternator isn't working. Back in the day, even if the battery goes dead as long as the alternator is working the car will still run. It won't start, but it will still run.

So I need to recover from my gas gauge stupidity and my alternator issues before I can ascertain if I'm having a fuel delivery issue. Thanks for the lesson. I seem to be getting a lot of those since I became a BMW owner.

Thanks again,
Mike

[slofut]

Hey Chris:
Thank you for the info on the fuel system, but before I tackle that I have to get past some other stupid stuff. As follows.
First, yesterday i decided to try the "Seafoam" treatment that is used on 850's. The gas gauge "looked" like it had about 1/8 to 1/4 of a tank. Not being familiar with e24's, I figured the little red light by the "R" was lying or there was one really big reserve in this thing. So I promptly hopped in and took off for the gas station, which, is 5 miles away. At about the 2 mile mark, it started to act weird again, right up until it ran out of gas. Got it home, put some gas in and it ran great. Put non-ethanol premium in it. Runs great, just a little rough. Probably needs a tune-up. Wait, there's more.

Today i got in it, ran some errands then on the way home it started the "weird" again. It died coming in the driveway. Battery was dead. Apparently the alternator isn't working. Back in the day, even if the battery goes dead as long as the alternator is working the car will still run. It won't start, but it will still run.

So I need to recover from my gas gauge stupidity and my alternator issues before I can ascertain if I'm having a fuel delivery issue. Thanks for the lesson. I seem to be getting a lot of those since I became a BMW owner.

Thanks again,
Mike

Yep, You're hooked!