engine cut-out - '88 535i

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ZINZ
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Joined: Oct 21, 2013 9:30 AM
Location: Cedar Park, Texas

engine cut-out - '88 535i

Post by ZINZ »

I've reached out to so many folks, but still can't sort this out.

1988 535i, was a Sport Auto, now has a 5 speed, 82,000 miles and bone stock. Never had this problem before about 2 months ago. I had just replaced all sorts of things to bring it into the best condition I could. I took it for a test drive and during a hard pull on the highway the engine cut-out for a microsecond and back on again. I limped it home and it continued to randomly cut-out. Each occurrence the Economy Meter would swing wildly to the left and the tach would jump slightly and then fall. Then it would run perfectly again.

I've been back through everything I did several times now and the gremlin persists. Twice, the engine would go into a surging, high idle and run very poorly (fuel/air/timing off completely). I can turn it off and it will restart immediately and idle beautifully...what the hell?

Most of the time the gremlin manifests itself into this cut-off where the tach jumps slightly and the economy meter swings wildly to the left. Sometimes the engine dies completely, mostly it simply hesitates and idles nicely again for a few moments before it cuts out again. This can happen at any load, any throttle position. It mostly occurs after the car is completely warmed up, but it has also acted up while it was warming up, but never when it is completely cold.

Here are the things I had initially replaced almost 2 months ago:

all new vacuum lines - alllll of them, big and small
new air boot
new intake elbow
new air filter
all new fuel lines
replaced both fuel pumps with one in-tank pump
new fuel pressure regulator (it was bad)
new O2 sensor
new plugs (WR9LS gapped to 0.027")
new wire set
new Bremi cap and rotor
rebuilt AFM (cleaned sweep and such) it ohm'd perfectly
valve adjustment (really only 2 were slightly out)
cleaned throttle body (didn't remove it, just cleaned it from the throat)

When the engine cutout started I then did the following; all with no cure to the cutout:

cleaned all grounds (did all that when I bought the car 2 years ago)
cleaned fuses
cleaned relay contacts (replaced Main and Fuel pump relays, too)
cleaned ICV
replaced both reference sensors (though they both ohm'd correctly)
replaced CTS and tightened up that connector
bypassed OBC relay box
swapped in a known-good DME (many thanks Sherman)
unplugged O2 sensor
unplugged TPS
unplugged the ICV
swapped in a different coil and wire
replaced Bremi cap and rotor with a Bosch parts (Bremi parts look a LOT better, by the way)
checked TTS - it ohms within spec and like I say, the gremlin does not occur when the engine is cold
cleaned C101 and C103 connectors
I pulled the in-tank pump and put the OEM stuff back on - no change

I've pulled on every harness, connector, wire, vacuum line, etc trying to pinpoint the culprit... no dice

Fuel pressure is dead-steady 40psi (on my gauge, at the high pressure line to the rail), even when the engine is doing its surging high idle

Oddly, I can no longer reset the SI lights (had changed oil during this time and now can't reset the SI) ...maybe this is a clue??

It must be in the harness, somewhere... I am stumped and haven't been able to drive the car for 2 months. Sure hope someone can help me out. I have videos that show the tach jump-economy meter swing and one of the surging high idle.

Thanks a bunch,

Ed Z
Cedar Park, Texas
cek
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Re: engine cut-out - '88 535i

Post by cek »

Make sure Fuse 6 is seated very tightly. I know you said you checked it, but it is very common for that fuse to get loose in it's holder, esp when hot.
ZINZ
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Location: Cedar Park, Texas

Re: engine cut-out - '88 535i

Post by ZINZ »

cek wrote: Nov 04, 2020 2:16 PM Make sure Fuse 6 is seated very tightly. I know you said you checked it, but it is very common for that fuse to get loose in it's holder, esp when hot.
I just triple checked it. It's clean and snug in its holder.

Con someone confirm something about the fuse box... I've been told it is grounded to the fender by it's mounting screws; is that true? I haven't removed it to see... would be easy enough if that is a known culprit.

Ed
tn535i
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Re: engine cut-out - '88 535i

Post by tn535i »

Any instant on/off loss or hiccup like you describe has probably got to be electrical. The fact the econometer swings seems to point that direction also. I think the DME does the calculation based on fuel injector commands so it seems like loss there. Otherwise you've replaced all the common things I would think of. Did the same things happen with both DME's. I would look at the ETM for any power, ground or signal sources to the DME that might give issues if an intermittent drop.

When you say you have checked all grounds do you have a ground between the valve cover and firewall by the DME and I'll assume you checked the injector/sensor grounds to the head.

Your right Bremi ignition seems better than Bosch and I've had some bad experience with Bosch (rotors especially).

I did not think the fuse box had anything in it that needed grounding unless maybe a relay. It's power distribution and not really using any power.
ZINZ
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Re: engine cut-out - '88 535i

Post by ZINZ »

I have swapped DME, coil with wire, and AFM with no change. Car begins to warm up and the problem reveals itself.

Here's a very strange example... I had the car on jack stands replacing the reference sensors (one at a time and checking if either solved the problem). I started the car and it ran beautifully for 20-30 minutes; I figured, go for a test drive and see if it's cured. As soon as I jacked the car off the jack stands it began to cut out! I lowered the car back onto the stands... the problem seemed to go away. I jacked it up again and it started cutting out. I was using the front crossmember under the engine to lift the car... if that provides any clues ??? it seems to be a grounding issue to me, but damned if I can locate the problem. The ground from the right engine mount to fender is clean and tight...

Ed
cek
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Re: engine cut-out - '88 535i

Post by cek »

Grounds strap from head to firewall?

Ground strap from engine mount to frame?
ZINZ
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Re: engine cut-out - '88 535i

Post by ZINZ »

Ground strap from head to firewall, clean and tight
Ground strap from engine mount to passenger side fender, clean and tight
Ground point at battery to driver's fender, clean and tight
Ground point from main harness to back of cylinder head, clean and tight
Ground point under dash/steering column, clean and tight
craigb93
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Re: engine cut-out - '88 535i

Post by craigb93 »

I would remove each ground strap, one-at-the-time and substitute using a jumper cable.
Very probably one cable somewhere has a loose or corroded end that you can't see. I chased that problem last year on my Bobcat. A casual pull on the cable didn't show any problem. Lying on the bench my Neg cable was corroded inside the lug, not visible when installed.
-Dick
ZINZ
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Re: engine cut-out - '88 535i

Post by ZINZ »

craigb93 wrote: Nov 08, 2020 12:20 AM I would remove each ground strap, one-at-the-time and substitute using a jumper cable.
Very probably one cable somewhere has a loose or corroded end that you can't see. I chased that problem last year on my Bobcat. A casual pull on the cable didn't show any problem. Lying on the bench my Neg cable was corroded inside the lug, not visible when installed.
-Dick
That's a great suggestion, Dick. The ground straps are easy to replace, but the bigger terminal ends of the harness looms may be trickier... I'll see what I can find. I agree that ground is dropping out somewhere.

Ed
Philo
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Re: engine cut-out - '88 535i

Post by Philo »

On my M5 the fuse 6 issue happened a lot. The fuse looked good but I replaced it anyway and tighted up the prong ends and the cutting out went away. My car use to cut out on the freeway doing 80mph. Scary.
Chimi-Changa
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Re: engine cut-out - '88 535i

Post by Chimi-Changa »

How much fuel was in the tank when it cut out getting on the hwy?

I hear fuel starve can happen even with the single pump conversion. Do you have the factory pumps to throw back in and give her a go?
ZINZ
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Re: engine cut-out - '88 535i

Post by ZINZ »

Philo wrote: Nov 14, 2020 2:49 AM On my M5 the fuse 6 issue happened a lot. The fuse looked good but I replaced it anyway and tighted up the prong ends and the cutting out went away. My car use to cut out on the freeway doing 80mph. Scary.
I replaced #6 with a brand new fuse. I can't be certain, but this may have helped... but the cut out still occurs.

I just drove it and it would only cut out under a hard pull. Perhaps now like a fuel starvation issue.

To answer Chimi Changa... the cut out occurred with full tank and empty tank; no difference. I was told to put the old pumps back on.. it made no difference. It is now running with the old pumps.

So... it seems the symptom has changed slightly in this latest test run. Before, then engine would cut out and EVERY time the Economy Meter would swing dramatically to the left. Today, the engine cut out and the Economy Meter didn't really move. The tach would fall, but the Economy Meter didn't swing like before. The car runs like a top, pulls very hard..until it cuts out.

Unfortunately, I can not see the fuel pressure gauge while I'm driving, so I can't tell if today's change is now a fuel related cut out. I'll keep testing and perhaps re-plump the fuel pressure gauge where I can see it from outside the hood.

Thanks for the continued suggestions,

Ed Z
uzayas
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Re: engine cut-out - '88 535i

Post by uzayas »

As I know , economy gauge only works with both fuel rate signal + velocity signal present. If I were you will check them.
Mike W.
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Re: engine cut-out - '88 535i

Post by Mike W. »

ZINZ wrote: Nov 17, 2020 2:14 PM

I just drove it and it would only cut out under a hard pull. Perhaps now like a fuel starvation issue.
Fuel starvation is more gradual, not a on/off cutoff unless the injectors stopped firing.
So... it seems the symptom has changed slightly in this latest test run. Before, then engine would cut out and EVERY time the Economy Meter would swing dramatically to the left. Today, the engine cut out and the Economy Meter didn't really move. The tach would fall, but the Economy Meter didn't swing like before. The car runs like a top, pulls very hard..until it cuts out.
I'm not seeing it on the diagram at the moment, but I believe the tach gets it's input from the ignition side, which would make sense. If the Econ meter is still functioning I'm guessing it's still delivering fuel or at least thinks it is.
Unfortunately, I can not see the fuel pressure gauge while I'm driving, so I can't tell if today's change is now a fuel related cut out. I'll keep testing and perhaps re-plump the fuel pressure gauge where I can see it from outside the hood.

Thanks for the continued suggestions,

Ed Z
ZINZ
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Re: engine cut-out - '88 535i

Post by ZINZ »

I just drove it on an errand to the bank. It drove beautifully for 15 minutes, then sitting at the drive through it cut out, but didn't die. It cut out most of the way home, but seemed to only do it near idle conditions. Cruising in 2nd gear with revs a constant 2500-3000rpms, it never faultered. Pull to a stop sign and it would cut out...along with the Economy Meter swing.

Also...when I shut the car off in the driveway, I noticed the tach jump up dramatically as I turned it off. I restarted the car and turned it off again.. the tach simply fell like normal.

Could the ignition switch be faulty?
tn535i
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Re: engine cut-out - '88 535i

Post by tn535i »

In answer to your last question yes... (cannot remember what's been eliminated or replaced or already discussed) but then...

or the wires/connection at the switch, or the connections behind the instrument panel, or the immobilizer, or the trip computer that triggers the immobilizer, or the connections under the hood, or the relay(s) (even if new), or connections to the relay, or connections at the DME, or grounds (still), or even just the + cable that piggybacks on the starter cable, or the C101 that gives power to the coil, or probably a few more I could come up with...

If you have the trip computer with code... I would remove the instrument cluster and then find the green wire that breaks the ignition down to the immobilizer relay and unplug those two pairs and put the harness back together as if it did not have the immobilizer. Then I would re-seat every connection in and around the ignition and such and clean and tighten the grounds under the dash. I would also clean the wires that piggyback on the battery cable (even if you think you have already) and put that back together, then clean and re-seat the C101 now see if the problem goes away. These I just mention specifically have all been discussed here before as root cause for drop in power to keep engine running.
ZINZ
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Re: engine cut-out - '88 535i

Post by ZINZ »

Thanks for the additional info and places to look.

I am to the point of handing it over to a trusted professional here in the Austin area. I've quite lost my patience with it... over 2 months now I have not been able to drive it.

I'll keep y'all posted if we ever have that "Ah HA!!!" moment..

Happy Thanksgiving everyone,

Ed Z
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