Author Topic: Diagnosing drivability; what say you? (Read 4275 times)

blalor · « **on:** July 03, 2011, 06:52:11 AM »

[cross-posting from r3v]

This may turn into a chronicle of fixing myriad small problems with my '91 318is, or it may be short and sweet if I find the crucial part or someone gives me a really good tip. Here goes!

Bought the car last February with 182k or so miles on it. About 1k miles and 30 days later, the idler sprocket lost its bearings, the timing chain slipped, and all the intake valves bent. FredK hipped me to another engine the next state over and I've been running another M42 with about 145k miles.

I've had some minor drivability problems that didn't really change when I put the new motor in (at which time I also replaced a slew of parts at the same time; pretty much every rubber or plastic coolant or vacuum part is now new). I've also been living with a hard start that's noticeable when it's warm out and much worse when it's cold; the engine'll crank and crank before finally firing up. Once running and warm, it feels pretty good, but has a stumble off idle. It also smells like it's running rich after it's started.

So, wind the clock back a couple of weeks. The car starts running *horribly*, check-engine light points to the AFM. Turns out I'd left the PCV hose disconnected. :mad: I started reading Charles Probst's Bosch fuel injection book published by Bentley, realized this stuff isn't that complicated, and dove in.

My AFM has dodgy resistance readings. My analog multimeter shows non-linear resistance when moving the vane from closed to open, and at fully open, the resistance dances quite a bit. I bought another AFM, and that one doesn't change resistance AT ALL. The car runs with both of 'em, the new one has bodged studs for the air box cover, so I went back to my old one. I'm trying to get a couple of folks to give me the readings from their M42 AFMs; if you'd like to contribute, please do! The AFM could be the reason for the stumble off idle, if it's not telling the computer that more air is flowing (or if there's a mismatch with the throttle position sensor).

I've tested the throttle position and engine temperature sensors; both look normal. I haven't plotted the temp sensor resistance against temperature, however, so it's possible it's not working correctly, but at 70�F or so, it looks right according to the E36 Bentley manual.

Today I decided to take a look at the injectors, thinking maybe they're dirty or leaking or something. As I was disassembling the intake, I noticed that the gasket between the upper and lower halves of the intake were wet, and I'm pretty sure it was gasoline. There intake just behind the throttle body was also wet. And the gaskets between the lower intake and the head were also a little wet, mainly on cylinders 2 and 3. :eek: It also appeared that zero fuel came out of the return line when I disconnected it from the fuel rail. This makes me think the fuel pressure regulator is blocked and not allowing ANY fuel to return, but it's possible that it could have just drained back to the tank (the inside of the line looked dry, however). I finally managed to pry the injectors out of the intake and the fuel rail. That was a complete pain in the ass and I'm hoping I didn't break any of them (one I'm not so sure about). They look fine, but I'd like to hook them up to check the spray pattern and look for leaks.

Tonight I borrowed a fuel pressure gauge. Since the intake and fuel rail are completely disassembled, I can't check the pressure of the system (tomorrow morning, hopefully), but I did do a static test with the gauge on the high pressure line to the fuel rail. I think my pump is bad: even after pumping for 20 seconds, it barely gets to 40 psi. The pressure does not build quickly and linearly to the spec of 43.5 psi. And after about 15 minutes it's already lost more than 7 psi. And the pump's kinda noisy. I'm going to look into pulling the pump tomorrow to check for a clogged pickup. The lines between the tank and the hard fuel lines look original; hopefully none of them are restricting the pressure, but I'd only expect them to restrict the flow. I replaced the hard fuel lines a couple of months ago. I need to return the fuel pressure gauge by Monday evening, so I'll have to wrap up my pressure testing soon.

Please let me know if you've got any thoughts on what I've reported here. I'm particularly interested to know why the intake seems to wet. I was thinking that if the fuel pressure regulator weren't working and the pressure was building too high that I could be getting excess fuel in the intake. Could still be happening if the injectors or their seals are leaking�

DesktopDave · « **Reply #1 on:** July 03, 2011, 10:52:57 AM »

I just had mine apart this weekend to do the hose delete mod. Both my paper intake manifold gaskets were loaded, but I'd guess it's an oil/gas mix. That's pretty normal from what I've seen, as our cars have no provision for catching crankcase gases. It looked to me that the gaskets were still functional.

My AFM does increase resistance as the door opens, in a generally linear fashion. I'd try to fix that up first before condemning the fuel system. You're probably right that both are wrong but I'd fix the AFM first. I'll bet that many of the BMW units are interchangeable, even though ours has a different connector. I'm not totally sure about that, but I've seen the Porsche & Volvo guys messing around with them too. How different could they be?

blalor · « **Reply #2 on:** July 03, 2011, 12:28:43 PM »

"How different could they be?" I'll leave that one alone, for now.

I reassembled the top half of the engine (everything from the head on up) and continued to test the fuel pump. Here's a quick video of the closed loop test (including the pressure regulator and return line):
http://www.youtube.com/watch?v=8Z2yb9Eg41A

The pump actually cut out a few times. You can hear the ticking of the pump, if you turn up the volume enough. I'm using a toggle switch on the jumper wire.

With the engine idling, the pressure barely makes it to 35, and drops to 30 as soon as you give it some gas. And it drops 10 PSI in just a few minutes of being turned off, so the check valve is bad, too. With that little pressure, it's no wonder the return line is dry; the regulator's not doing anything! Also, there's a note in the Bentley manual that if the high pressure line is blocked, pressure can rise to as high as 87 PSI! So, yeah, the AFM's probably bad, but the pump's worse. I pulled the pump to see if there was anything clogging it, but it looks fine. I'll be placing an order tomorrow, as soon as I find the cheapest price, but I'll probably end up using RMEuropean.com.

DesktopDave · « **Reply #3 on:** July 03, 2011, 12:31:23 PM »

There's a post somewhere on the site about a generic fuel pump for our cars. I think it's a Summit part. Let me see if I can find it.

blalor · « **Reply #4 on:** July 04, 2011, 06:01:07 AM »

I did find this on eBay: 82-91 BMW E30 WALBRO FUEL PUMP 316 318 320 323 325 M3 I'm suspect of anything that lumps the '91 318is in with anything else because the OEM part numbers are different… According to RealOEM that pump is only used on M42 cars. The fuel tank, however appears to be the same for most of not all E30s. Maybe it would be OK, then. $93 sure beats $242 (ECS).

blalor · « **Reply #5 on:** July 04, 2011, 06:13:37 AM »

I found this pump at Summit for $60. The pictures aren't encouraging, even though the application specifically notes the '91 318is. Hm. Maybe I should give 'em a call… Stupid holiday.

bmwman91 · « **Reply #6 on:** July 04, 2011, 12:13:16 PM »

With aftermarket pumps, you need to do a little Dremel-ing. Look around here for an install of a TRE Performance 255LPH pump. Someone took good pictures.

With the AFM, do the values get dodgy only when moving the vane? As the door opens, the resistance should only go one way, period. If it goes up & down as the door opens, the carbon track is pooped.
EDIT:
The above statement is WRONG. I had an old AFM open today to measure some stuff for the MAF conversion, and the resistance between the output & ground (pins 2 & 5) should go up & down, with the overall trend being up. When you push the vane to the very end / 100% open, it should drop again. Hpwever, if you applied 5V between pins 1 & 5, you would find that the output voltage on pin 2 increased linearly, with no up & down nonsense. There's a fairly elaborate system if series-parallel laser-trimmed resistors parallel to the carbon wiper track that are used to precision calibrate the unit, and those will make the resistance values measured externally look weird. As long as the resistance is between ~60 Ohms & ~800 Ohms you are good.

I recommend checking the overly-complicated rubber part that the PCV hose plugs into under the intake. I replaced mine about a month ago, and it has already split in half, providing another nice vacuum leak. It seems that a number of hose parts are now made by CRP Industries (China Rubber Products?)...it's one vowel short of describing what it actually is! Anyway, I got some generic ventilation hose from the local parts store & just used that to connect the PCV hose's union-barb directly to the throttle body. It is a good idea to put in an oil catch filter too...it'll keep the intake from getting so gunked up.

DesktopDave, the AFMS are similar in that their resistance increases logarithmically as air flow increases (sensitive at low flows, not so sensitive at high flows). The output is generally something like: A*ln(flow)-B. The A & B vary between AFMs. At low-load conditions, they are probably close enough to each other that the O2 sensor could cover for them. At high load, particularly open-loop WOT mode, the ECU will be running severely lean with an AFM designed for a bigger motor. They aren't interchangeable, functionally. The guts are all the same though. There's a plastic gear that sets the pre-tension on the spring, and as far as I can tell the pre-load is all needs to be varied between models (and maybe the little idle-pot screw for fine calibration).

blalor · « **Reply #7 on:** July 05, 2011, 05:31:40 AM »

Quote from: bmwman91;105044

With aftermarket pumps, you need to do a little Dremel-ing. Look around here for an install of a TRE Performance 255LPH pump. Someone took good pictures.

Ok, looks like this is the pump: BMW 318 255 LPH Fuel Pump 1990-1999 SKU: TRE-340

I know you used this pump, but man, their site sketches me out:

Quote

This brand new TRE-340 255 LPH high pressure in-tank fuel pump flows about 235lph at 13.5v and 40psi

Uh, whut? The 255 LPH pump flows 235lph? Does it somehow flow more at 12v? I get that it's quieter, but if these guys are saying they're like the Walbro but quieter, it makes me think they can't really stand on their own 2 feet, y'know? They're also providing the cheap worm-style clamps that you're not supposed to use with high-pressure fuel line. Oh, and non-submersible fuel line? Urg.

TREPerformance doesn't seem to make anything themselves and don't say where stuff's made, so I'm assuming it's probably all coming from China. The Airtex pump I linked to on Summit's site is almost certainly Chinese, as well; one of the few non-Summit links I found for it was Alibaba.

Walbro (or at least their pumps) have been acquired by TI Automotive. Can't tell where they make their stuff, either, but it may be Japan.

So all of these aftermarket pumps must use the existing mounting bracket, eh?

Ok, I think this is the write-up you were talking about: DIY Fuel Pump Replacement. There's another one on r3vlimited, but I don't think it's for the M42: DIY - Walbro 255 fuel pump retrofit

Oh, so the write-ups I've seen show the brass/rubber connector thingy on the stock pump being replaced with some hose. I'm assuming that thing isn't essential to the operation of the pump, then? I thought it might be the check valve (which is apparently also bad on my car).

blalor · « **Reply #8 on:** July 05, 2011, 05:46:21 AM »

Quote from: bmwman91;105044

With the AFM, do the values get dodgy only when moving the vane? As the door opens, the resistance should only go one way, period. If it goes up & down as the door opens, the carbon track is pooped.
EDIT:
The above statement is WRONG. I had an old AFM open today to measure some stuff for the MAF conversion, and the resistance between the output & ground (pins 2 & 5) should go up & down, with the overall trend being up. When you push the vane to the very end / 100% open, it should drop again. However, if you applied 5V between pins 1 & 5, you would find that the output voltage on pin 2 increased linearly, with no up & down nonsense. There's a fairly elaborate system if series-parallel laser-trimmed resistors parallel to the carbon wiper track that are used to precision calibrate the unit, and those will make the resistance values measured externally look weird. As long as the resistance is between ~60 Ohms & ~800 Ohms you are good.

Thanks for that clarification.

I bought another AFM a few weeks ago. The resistances between pins 2 and 5 don't change at all, yet the engine still dies if I hold the vane open, and my oscilloscope still shows a fairly linear voltage output with the engine running. I find that *really* confusing.

Page ELE-71 of the E36 Bentley manual has a pretty good diagram of the entire AFM:

That didn't help me figure out how the output voltage can vary when the resistances don't, however� And how do you get at that adjustment pot? The AFM I cracked open has it, but the plug seems to be sealed shut.

Quote from: bmwman91;105044

I recommend checking the overly-complicated rubber part that the PCV hose plugs into under the intake. I replaced mine about a month ago, and it has already split in half, providing another nice vacuum leak. It seems that a number of hose parts are now made by CRP Industries (China Rubber Products?)...it's one vowel short of describing what it actually is! Anyway, I got some generic ventilation hose from the local parts store & just used that to connect the PCV hose's union-barb directly to the throttle body.

I checked that line this weekend and it seems to be good. I sucked on the hose (making sure there wasn't any of that white foamy crap I've seen in there before!) and it held vacuum. I replaced all that stuff about a year ago with OEM parts from RMEuropean.com. I really like those guys, by the way. I also did the "mess under the intake" clean-up. I still think I might have a vacuum leak, but it could also just be intake noise. I need to do a little more poking around, but once I fixed the leaking fuel pressure regulator vacuum line (had a 1/2" hole) the idle did smooth out.

Quote from: bmwman91;105044

It is a good idea to put in an oil catch filter too...it'll keep the intake from getting so gunked up.

How and where do you put one of these in?

blalor · « **Reply #9 on:** July 05, 2011, 12:52:35 PM »

I picked up a fuel pump from AutoZone this afternoon. Not convinced about the quality (shocker), but the price is about break-even with the Airtex pump from Summit when you include shipping. Hopefully I'll have it installed tonight. I also rented another fuel pressure gauge from them.

bmwman91 · « **Reply #10 on:** July 05, 2011, 12:53:58 PM »

The resistance between pins 1 & 5 (+5V & ground) should remain constant. Pin 2 is the vane's wiper & that is the one that should give varying resistance readings.

I got some generic oil catch filter things from McMaster. A little PCV hose cutting & some work on the lathe to make adapter bushings & I was set. You can probably find some generic rubber bushings at Home Depot to make things fit. The filter I used is an in-line type with small hose barbs that needed beefing up to fit tightly in the PCV hose.

blalor · « **Reply #11 on:** July 05, 2011, 08:44:50 PM »

The pump I found at AutoZone turned out to be the same Airtex E3240 pump that Summit sells. The pump and the separate filter sock were about $100, so probably $10 more than buying from Summit and waiting for delivery. It was a pretty straightforward install; the hardest part was deciphering the instructions which were made up four different languages, all interleaved. It does *not* come with the bracket, so I had to splice and solder the wires into the connector on the pump bracket. I reused that weird coupler thing instead of going with straight hose.

I borrowed AutoZone's fuel pressure gauge and confirmed that the pump provides pressure almost immediately. The regulator looks kind of borked, tho:
http://www.youtube.com/watch?v=e5vLBzhQgAY

Pressure with the vacuum hose disconnected stays at around 52 psi no matter how much I rev the engine. With the hose connected, as you can see in the video, it never goes below 35, but it doesn't stay at 43.5 the way it's supposed to. So I guess I'll have to order up one of those next.

I haven't been able to drive it, yet.