SOLVED-86 635csi - Post Tuneup Rough Engine Operation

E28 technical advice asked and given! Troubleshooting, modifications and more.
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The Don
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SOLVED-86 635csi - Post Tuneup Rough Engine Operation

Post by The Don »

SOLVED-Plug wires were not connected to their proper location on the distributor cap. I connected them according to the firing order. As opposed to using the cylinder numbers.

Just performed a tuneup on my 86 635csi and the engine feels terrible now. My notes are below. Not sure if these issues are related to the parts I changed or purely coincidence (the latter would not surprise me). Any help would be appreciated. Link to some videos are below.

https://photos.app.goo.gl/KdQyUuPedUG8GkL98
https://photos.app.goo.gl/F5KnzcWpr1c1Upkb6

Problem: After tuneup, engine struggled to start and stay running. Engine would start, stumble, and die. Pressing the gas made the RPM climb slowly, but the engine stumbled/bucked as it climbed. Feels like a lawn mower engine or the timing is off.

Parts Changed: Distributor Cap (Bremi), Distributor Rotor (Bremi), Spark Plugs (Bosch WR9LS), Air Filter (Mahle), Valve Cover Gasket (Victor Reinz)

Cleaning: Outside of Plug Wires (shop towel and cleaner), Inside of Throttle Body + Plate with Brake Cleaner (did not remove), Inside of ICV with Brake Cleaner, Cylinder Head Surface with Scraper + Brake Cleaner on Rag, Inside of Valve Cover Breather Hose, Sanded Ground Wire Lug for Firewall-Valve Cover Attachment (confirmed its torqued on)

Measurements
Speed/Ref. Sensor - Both Okay
  • 1-3 Terminal ~ 1029 & 1038 Ohms respectively
    1-3 Terminal, 2-3 Terminal, ‘O.L’ displayed on my multimeter (hindsight, pretty sure I had the incorrect range selected)
    One sensor’s connector end is cracked
    Unplugged both and car would crank but not start
Ignition Coil (0221118335) - Primary and Secondary Okay
  • Primary - 0.6-0.7 Ohms
    Secondary - 5890 Ohms
    Ignition Wires (including coil wire) - Okay
    1 to 6 ~ 5700-6000 Ohms
    Coil ~ 2100 Ohms
2nd Adjustment/Inspection
  • Replaced distributor cap + rotor with original Bosch >> slight improvement >> engine started and stayed running– still runs really rough and sounds like a lawnmower engine when trying to climb through the RPM range
    Removed all intake related hoses/boots up until the throttle body and inspected for cracks, no issues found
    Noticed air filter was upside down– corrected
    Pulled oil dipstick while running and the engine RPM dropped
    Checked to make sure the valve cover is clamped evenly across the cylinder head and there are no gaps– confirmed
    Jumped Fuel Pump Relay (pin 30 to pin 87), felt fuel going through feed line
    Removed fuel feed line
    Slightest bit of fuel came out of the line (kind of weird) >> I do have a fuel pressure gauge I can rig up to check the actual fuel pressure
    Swapped Fuel Pump Relay with known good one - no change
    Swapped Main Relay with known good one - no change
Last edited by The Don on Sep 25, 2022 3:39 PM, edited 2 times in total.
kojo96
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Re: 86 635csi - Post Tuneup Rough Engine Operation

Post by kojo96 »

Did you by chance unplug the AFM? Pretty easy to have forgotten to plug it back in.
The Don
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Re: 86 635csi - Post Tuneup Rough Engine Operation

Post by The Don »

Was my first instinct as well. Definitely plugged in.
LarryM
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Re: 86 635csi - Post Tuneup Rough Engine Operation

Post by LarryM »

Maybe you knocked a vacuum hose loose? Or if you were moving things around maybe opened up a crack in an old rubber component, such as the intake bellows.

Edit: Oh I see you checked that. But a vacuum leak would be my first guess.
Mike W.
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Re: 86 635csi - Post Tuneup Rough Engine Operation

Post by Mike W. »

I'm sure you were careful, but double, triple check that the spark plug wires are going to the right place. Sounds dumb, but it's happened. If that checks out look for a vacuum leak. Maybe something you forgot to connect, maybe a lip folded over and not sealing, maybe something cracked in the R and R, but somehow a vacuum leak. But check the plug cables first.
The Don
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Re: 86 635csi - Post Tuneup Rough Engine Operation

Post by The Don »

Checked the plug wires multiple times. I actually labeled them before I unplugged them from the cap. There was one instance where I had two flipped and after correcting it did not make much of a difference.

I'm going to double check for vaccum leaks. Assuming this would have be a large leak after the AFM to run like this.

Last, I did notice a weird t-tap between the CSV and wiring going into the injector loom. I didn't dismantle it as the car was running fine as-is before the tuneup, so I wanted to leave it be for the time being. Hypothetically speaking, if I knocked loose the connection to the CSV, would that be a problem (I'm assuming no).

https://photos.app.goo.gl/PooKPMDmnEvtf6wN6
Mike W.
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Re: 86 635csi - Post Tuneup Rough Engine Operation

Post by Mike W. »

The Don wrote: Jul 26, 2022 10:12 AM

Last, I did notice a weird t-tap between the CSV and wiring going into the injector loom. I didn't dismantle it as the car was running fine as-is before the tuneup, so I wanted to leave it be for the time being. Hypothetically speaking, if I knocked loose the connection to the CSV, would that be a problem (I'm assuming no).

https://photos.app.goo.gl/PooKPMDmnEvtf6wN6
That is odd, but no, the cold start valve is just for starts, at most it only functions when the starter is cranking, it's not a warm up device.
Federico
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Re: 86 635csi - Post Tuneup Rough Engine Operation

Post by Federico »

Did you properly reconnect the vacuum hose between the valve cover breather hose and the bottom of the intake manifold?
Mike W.
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Re: 86 635csi - Post Tuneup Rough Engine Operation

Post by Mike W. »

Mike W. wrote: Jul 26, 2022 11:20 AM
The Don wrote: Jul 26, 2022 10:12 AM

Last, I did notice a weird t-tap between the CSV and wiring going into the injector loom. I didn't dismantle it as the car was running fine as-is before the tuneup, so I wanted to leave it be for the time being. Hypothetically speaking, if I knocked loose the connection to the CSV, would that be a problem (I'm assuming no).

https://photos.app.goo.gl/PooKPMDmnEvtf6wN6
That is odd, but no, the cold start valve is just for starts, at most it only functions when the starter is cranking, it's not a warm up device.
I should qualify the above is how it's intended to work. I suppose someone might have hooked it up as an enrichment device in an attempt to get more power, in which case just pull the connector off the csv. It'll start without it in all but the very coldest weather, and maybe even then.
The Don
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Re: 86 635csi - Post Tuneup Rough Engine Operation

Post by The Don »

Confirmed the vaccum line is connected to the breather tube. Gonna pull the new plugs out this week and see if anything looks suspect.
The Don
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Re: 86 635csi - Post Tuneup Rough Engine Operation

Post by The Don »

Reading through the moronic troubleshooting guide and it mentions that a culprit CSV could cause this type of condition. Going to diagnose tomorrow. I looked a little closer at the t tap today and this is what I gathered.

Plug going into CSV has a BLK/YL and solid White (beige looking) wire. The tap is on the white wire and is tapping in a black wire that goes to a ground junction on the cylinder head.
Not sure if the original ground gave out and someone 'jumped' a ground to get it working.

I also looked at the wiring diagram and it shows a BLK/YL + BLK/RD connection. Unless I am reading it wrong.
Mike W.
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Re: 86 635csi - Post Tuneup Rough Engine Operation

Post by Mike W. »

Just unplug the CSV. At the least just for testing.
The Don
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Re: 86 635csi - Post Tuneup Rough Engine Operation

Post by The Don »

Troubleshooting

1. Unplugged CSV >> started engine >> no change, still rough
2. Checked resistance of TTS >> w-ground 40ohms >> g-ground 50 ohms >> first reading is out of spec. according to the motronic troubleshooting guide
3. Rigged a fuel pressure gauge to the feed line >> without key in ignition, jumped fuel pump relay pin 30-87, gauge read 50psi >> once I disconnected the jumper, the gauge settled to 46psi >> this is above the spec.
4. Started engine with CSV disconnected + fuel pressure gauge rigged >> gauge read 50psi
5. Pulled all spark plugs to see their condition >> keep in mind these are brand new plugs that have seen little engine running time because I have been in diagnosis mode >> the spark plug in cylinder 1 closest to radiator is completely black, see picture.

So now I am thinking I have a combination of: leaking fuel injectors + a faulty FPR. Thoughts?

https://photos.app.goo.gl/XKDSZ5D6BmTZnAnn9
https://photos.app.goo.gl/hR1PJ7opSBdajGWE8
https://photos.app.goo.gl/MtQ5T9UEcBFfDbrS9

Here are the plugs that I replaced with new ones. If I do have a fuel issue now, no signs of that on the previous plugs. Would be bizzare that it happened right after doing a tuneup?

https://photos.app.goo.gl/WFCMdt7QKH6BuY5eA
Federico
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Re: 86 635csi - Post Tuneup Rough Engine Operation

Post by Federico »

I'd check the ignition wires for proper continuity/resistance, paying special attention to cyl 1 & 5.
Only after that would I pursue a fuel issue.
Mike W.
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Re: 86 635csi - Post Tuneup Rough Engine Operation

Post by Mike W. »

A very long shot is the CSV is leaking, perhaps badly. If your fuel lines are good clamp it off. But that's a 1000 to one possibility. Otherwise leave it unplugged, disregard the TTS and the whole cold start system.

I don't recall now, have you checked the O2 sensor readings? But even that can be misleading at times, if it's rich enough to cause a misfire, that cylinder won't fire, the O2 sensor will read the excess oxygen and richen the mixture. I ran into that condition once.

Just for shits and giggles, check your return fuel line. If it's restricted, it could cause high fuel pressure and all sorts of crazy things.

OT Side rant: Google. I could see your pics, and this isn't at you. But Google makes it so difficult, disables the image location, and have no less than 4400 lines of code for you to be able to show us one picture. Grrr, I remember when I liked Google. And I thought German auto engineers made it complicated.
The Don
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Re: 86 635csi - Post Tuneup Rough Engine Operation

Post by The Don »

Federico wrote: Jul 31, 2022 9:54 PM I'd check the ignition wires for proper continuity/resistance, paying special attention to cyl 1 & 5.
Only after that would I pursue a fuel issue.
I tested all wires already and they are okay. Will do another test and try to see if the readings change if I 'wiggle' the wires around.
Mike W. wrote: Aug 01, 2022 12:40 AM A very long shot is the CSV is leaking, perhaps badly. If your fuel lines are good clamp it off. But that's a 1000 to one possibility. Otherwise leave it unplugged, disregard the TTS and the whole cold start system.

I don't recall now, have you checked the O2 sensor readings? But even that can be misleading at times, if it's rich enough to cause a misfire, that cylinder won't fire, the O2 sensor will read the excess oxygen and richen the mixture. I ran into that condition once.

Just for shits and giggles, check your return fuel line. If it's restricted, it could cause high fuel pressure and all sorts of crazy things.

OT Side rant: Google. I could see your pics, and this isn't at you. But Google makes it so difficult, disables the image location, and have no less than 4400 lines of code for you to be able to show us one picture. Grrr, I remember when I liked Google. And I thought German auto engineers made it complicated.
Yeah I thought about the CSV possibly sticking open at all times. That is why I wanted to remove it and test for that condition.

In terms of getting the O2 sensor readings, I have never done that before. How is this done?

Last, I have disconnected the return line about (3) times now and each time there is barely any fuel coming out. On my other E24, if I remember correctly, there should be a decent amount of fuel that comes out? I can swap out a known good FPR from my other E24 just to eliminate that as a variable for the high fuel pressure readings.
Mike W.
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Re: 86 635csi - Post Tuneup Rough Engine Operation

Post by Mike W. »

The Don wrote: Aug 01, 2022 9:56 AM
In terms of getting the O2 sensor readings, I have never done that before. How is this done?
Easy. There is usually a connection in the engine compartment with a fat (shielded actually, not a HD wire) leading to a small boot under which is a 1/4" connector. Leaving it hooked up, push the boot down and hook up aligator clip test leads to it and ground and a multimeter. Use the 2VDC range. Ideally you will get readings going up and down almost randomly, but centering on .5, or half a volt VDC. Like .5, .8, .7, .2, .2, .5 etc. That's how it's supposed to be. It's not a linear device, but high, which will still be under 1.0 VDC is rich, and low is lean.
Last, I have disconnected the return line about (3) times now and each time there is barely any fuel coming out. On my other E24, if I remember correctly, there should be a decent amount of fuel that comes out? I can swap out a known good FPR from my other E24 just to eliminate that as a variable for the high fuel pressure readings.
Yes, there should be good flow out the return. It does sound like a bad FPR, but a weak pump can also create a low or no return condition. FPRs can also fail in such a manner that they allow fuel into the intake thru the vacuum line resulting in a rich condition.
The Don
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Re: 86 635csi - Post Tuneup Rough Engine Operation

Post by The Don »

8/2/22 Troubleshooting

Got to spend a little bit of time in the garage today. Here are the updates.

- Tried to remove CSV, but couldn't get good access to the bolts >> will likely just disconnect and cap off the hose next chance I get
- Cleaned spark plugs and reinstalled
- Changed FPR to known good one >> Fuel Pressure at 40 psi now
- Car cranks but will not start now >> battery has lost some juice so that could also be a reason >> I had a trickle charger connected but it's a really slow one (1.5amps or so)

I just got a Bentley Manual + an original BMW shop manual yesterday. Going to do some reading and find additional troubleshooting steps. Really want to find the root cause of this. Still planning to check the O2 sensor readings as well.

One of the flywheel sensors has a pretty bad cracked connector. I am thinking to change it since it's cracked badly and requires tape to stay together. But I doubt it's the problem since the ohm readings were within spec.
BDKawey
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Re: 86 635csi - Post Tuneup Rough Engine Operation

Post by BDKawey »

you mentioned you said you checked around the valve cover gasket but when I was younger I did an m20 valve cover and one of the "half moon" cam plugs fell out and essentially had a big vacuum leak.

best of luck and keep on keepin on
The Don
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Joined: Sep 17, 2007 11:46 PM

Re: 86 635csi - Post Tuneup Rough Engine Operation

Post by The Don »

BDKawey wrote: Aug 03, 2022 3:59 PM you mentioned you said you checked around the valve cover gasket but when I was younger I did an m20 valve cover and one of the "half moon" cam plugs fell out and essentially had a big vacuum leak.

best of luck and keep on keepin on
Thanks for the tip. Luckily, I can rule that out because the M30 motors do not have any of those 'cam plugs.' :D
gadget73
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Re: 86 635csi - Post Tuneup Rough Engine Operation

Post by gadget73 »

just out of curiosity have you tried putting the old rotor back on? I once got a defective rotor that arced through to the distributor shaft. Engine ran but horribly. I've also had distributor caps that had a missing center button from the coil, also makes things run horribly. Anymore I don't really trust parts just because they are new.
The Don
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Re: 86 635csi - Post Tuneup Rough Engine Operation

Post by The Don »

gadget73 wrote: Aug 04, 2022 9:41 AM just out of curiosity have you tried putting the old rotor back on? I once got a defective rotor that arced through to the distributor shaft. Engine ran but horribly. I've also had distributor caps that had a missing center button from the coil, also makes things run horribly. Anymore I don't really trust parts just because they are new.
I did. It currently has the original Bosch cap + rotor that were on the car.-- the new parts are now sitting in the trunk. Anecdotally speaking, the car ran incrementally better after I put these back in. Its hard to say if it actually made a noticeable difference. Once I have the car running normal, I will re-install the new Bremi cap + rotor.
The Don
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Re: 86 635csi - Post Tuneup Rough Engine Operation

Post by The Don »

So this is quite embarrassing to admit. The problem was I indeed had mixed up the plug wires at the distributor cap. I marked them with the firing order and reconnected them as such. Lesson learned!!!

Thanks for all the help.
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