E30 all new- won’t rev past 3-4-5k depending on CKP adjustments

[Rutech13]

Hi everyone.
I got 88 325e with 325i engine/harness/ecu/dash in it .
I got this car in barely running condition but after a full ending rebuild,new head was also installed .
im fighting ,what seems to be a simple problem at first ,a nightmare if my days .
Car will not rev past 3000 rpm,no matter at WOT or half throttle or even driving. All kinds of test and swaps and new parts done to it-nothing.
But here is a catch that stomps me . If I go and adjust CKP bracket all the way out and put few shims under sensor ,it brings me way out of recommended specs,but-car will rave up to 4000-4300 now-if I mess with it more I can achieve 5000-5300 but in that condition it takes more that 5 seconds of cranking to start it .
With that said-least start a discussion so I know what info y’all would want me to provide .

[Rutech13]

I’ll throw out here what have been replaced:
4 ecu’s(all kid of numbers)
4 CKP sensors (2oem ,1hella,1chinise)
FPR (oem was good but I still put hella I believe )
3 fuel pumps ,all tested good (bosh oem in it now)
2 TPS (oem and hella) both tested as they should
3 AFM -all tested perfect but still swapped it
Harmonic balancer
CKP sensor braket
Coolant temp sensor ECM side
plugs
3 engine coils
vlaves adjusted
fuel drained and refiled before pump replacement
Bosh fuel filter
ICV was good but still cleaned it just to make sure .
Grounds and powers are secured
alternator puts out 13.5 at idle
fuel pressure 38-42 psi at idle,45 ish at WOT
Fuel delivery 30sec/30oz

Got no stomp test on any of those ecu’s but connected the scanner and got no codes .

[It's Soda Not Pop]

Which DME's did you use? (meaning 173, 525, etc.) Stock chips in the DME's? Did you replace the cap and rotor? Does it break up at 3k rpms and then keep trying to rev past that? Or does it stop there like it is the limiter?

I was having issues awhile ago with my car. It would buck and misfire bad underload around 3k-4k. I went with a standalone with LS coils from ClassicDaily. All my problems went away. I replaced everything similar to you and I kept having the same problem. I believe it was in the ignition somewhere. Either way I went standalone and didn't look back.

Check you plug wires and make sure that the crimp hasn't come loose. I had bad wire one time that looked fine at a glance. But the crimp on the inside was bad.

[tomstin]

Have you tested all the circuits back to the ECU (continuity)? There is a connector under the intake on the "I" engines that is notorious for corrosion, make sure all those connections in that connector are clean.

[Rutech13]

It’s Soda Not Pop, ecm’s two 380 ,173 with chip .
i got donor car that runs only while cranking but even that thing would rev up to the sky.
Yes,just like a rev limiter-half throttle it nice and smooth but full throttle it goes “ratatatatata” but only at 3k unless I mess with CKP sensor
cap and rotor are new Berim and coil bosh .
if I set CKP sensor by Bentley book 1mm -/+.3 than I left with 3k rpm and periodically poop from exhaust ,but when I put spacers to bring it further away from h.balancer I achieve 4k and a little worth starting and idling conditions. And when I put it twice further away (2ish mm) from balancer I can achieve 5k+ but in this condition car will not start unless I bring sensor closer.



What stand-alone did you go with?

[Rutech13]

tomstin, I’ve check a few at ecu-yes. What exactly should I have check ?
Also it seems that I have early version of the i harness as I don’t have a circle injector harness plug and my injectors connect separately one by one .
car or connectors got no rust or corrosion
I’ve check relays fuses and 101 connector
🤷

[digger]

If it runs then the circuits obviously work. to get the the bottom of this from a root cause you need to scope out the VR crank signal when it runs and then when it plays up and see if that is the cause whether this be loss of signal fully, in part, excessive noise etc (most likely is as the change of air gap affects the result) and if not then also repeat on the same but on control side of the coil as IMO these are the two (2) most likely culprits.

for the case where the standalone ECU swap fixed things it is possible that a different ecu will have much better signal conditioning than the 1980s tech so can deal with a degraded signal without necessarily fixing the root cause

[Rutech13]

By “scoping” you mean oscilloscope?

[digger]

By “scoping” you mean oscilloscope?

yes here is an example from m42 but should be similar for m20

https://www.r3vlimited.com/board/forum/e30-technical-forums/engine-drivetrain/alternative-tuning-w-a-r-megasquirt-etc/341864-the-definitive-m42-crank-and-cam-angle-info-thread

[zaq123]

when you gap CKP too much, you loose sync hence your rpms go up, normal behaviour. You have probably some mechanical issue with TB plate/ cable etc or your ECU ids acting up.

[Rutech13]

Digger , got it🫡
But also got following -sensors from working cars and balancers too-ecms swaped and wiring sensor-ecm is good .

[Rutech13]

zaq123, throttle is new so as tps-in fact all was swapped over and over .
cables old bu raving by hand not making difference

[It's Soda Not Pop]

"Quote" for the case where the standalone ECU swap fixed things it is possible that a different ecu will have much better signal conditioning than the 1980s tech so can deal with a degraded signal without necessarily fixing the root cause: digger

For me after changing out everything several times (several brands) and still having the issue. I'll gladly take this "Band-Aid" fix of a standalone ecu.

I don't think it's his CPS. It's in the ignition I bet. If it is the CPS it's has be a bad spot in the harness then. I know for me the harness is the only thing I didn't change.

I believe JLevie was having a similar issue. Here is his write up about it:

08-24-2015, 01:12 AM
Engine Management Saga

The car was an early production (06/87) 325is. I replaced the 153 DME with a 173 well before this started happening and it ran fine for a couple of track weekends. When the problem first surfaced it might happen once in a while. But with time it progressed to happening a lot.

Around 5400-5800rpm the engine experienced a sudden and complete loss of power. It seemed to occur at higher rpm at the beginning of a track session, when the engine is relatively cool, and at lower rpm once everything is good and hot. From the driver's seat it feels as if the ignition was briefly switched off and there's no stumbling, misfires, or loss of power prior to the event. If I persist through the cut-off(s) the engine will pick back up and run to the redline.

I have noticed that the CEL will come on just before the event and when it happens the tach will drop a lot more would be appropriate for the loss of speed from coasting. On occasion I've seen it briefly go to zero. The CEL is so consistent with the loss of power that it could be used as a shift light. And the CEL extinguished as soon engine rpm was reduced by an upshift or by accelerating through the cut-off region. It didn’t appear to matter whether the critical rpm is reached at WOT or at partial throttle. Having to short shift at 5200-5300rpm on the track is a major irritant...


In an attempt to solve this problem (and fix other problems) I:

1) Replaced the O2 sensor (new OE part)
2) Swapped in a known good AFM
3) Swapped in a known good 173 DME
4) Replaced the injectors (new OE parts)
5) Replaced the crank position sensor (new OE part)
6) Replaced the TPS (new OE part)
7) Replaced the main & fuel pump relays (new OE parts)
8) Replaced the coil (new OE part)
9) Replaced ignition wires, cap, & rotor (new OE wires & parts)
10) Cleaned all grounds and primary power connections
11) Replaced intake manifold gaskets & all hoses and smoke tested the intake
12) Verified proper operation of the ECT sensor (and swapped sensors)
13) Proved there are no intake leaks in the brake booster
14) Replaced the oil filler cap and dipstick o-rings
15) Eliminated the evaporative control system
16) Acid cleaned & sealed the tank & replaced both pumps (new OE parts)
17) Replaced FPR (new OE part)
18) Checked C101 for corrosion
19) As of 10/28, replaced the alternator

With all of that done and other routine maintenance (timing belt, filters, valves adjusted, plugs, etc), the engine ran better than it probably has in quite some time. And I now have a nifty collection of good spares. But nothing I've done has had any affect on the problem.

I have proved that the used AFM and DME are good by installing them in another E30 and they behaved perfectly there.

The fault codes stored in the DME are 1251 and/or 1261. 1251 is an injector fault and 1261 is a fuel pump relay fault. The only thing I can think of to do at this point is to ohm out the wiring in the harness.

10/20/2007

I ohmed out all power and ground connections to the DME, coil, and injectors. Nothing remarkable there. But in checking power connections I did find that there's about 4.5ohms of resistance to the hot side of the coil, which means the ignition switch isn't quite healthy. Just for grins, I bypassed the ignition switch to feed power directly to the coil and DME "Start" input, to no affect.

Now I'm thinking that the prime problem may be 1251 (injector fault). If that fault, and only that fault, happens after a single event I'm inclined to figure out a way to bypass that part of the harness (even though it ohms out) to see if that fixes it.

10/21/2007

Now I know what it is. The car is possessed by demons. To fix it I need a young priest, an old priest, and a large jug of Bavarian Holy Water...

In trying to see if the injector fault code was repeatable I did several runs where I cleared the codes, duplicated the problem, and scanned the DME. The reported fault codes were completely random and different each time. Maybe the alternator is noisy?
As a next step I'm going to rig something up to allow in-car disconnect of the alternator and see if that changes anything.

10/28/2007

Since I had an alternator that just needed new brushes, I swapped alternators after fixing the spare. That didn't eliminate the problem, but it may have moved the event higher in the rpm band. It was happening at about 6k and the CEL would come on a couple of hundred rpm below the event. More testing was needed to see if it really has moved
higher.

Now I only getting a 1262, which is an idle speed control fault and may be related to the CEL that occasionally comes on while the engine is idling or during a long down hill closed throttle run. But that code can also be set by a stall above 600rpm. So it might be related to this problem.

I'm running out of the possibilities. The only thing I can think of to do now is to ohm out all of the wires in the engine harness. But I don't understand why a problem there would be rpm sensitive and not also cause cause problems at other engine speeds.

11/16/2007

I found the spec for the CPS air gap (1mm or.040") and discovered the CPS was a lot closer to the crank wheel than the spec calls for. I adjusted the gap, but that made the problem slightly worse. So it is looking more and more like a problem with the wiring harness and specifically the CPS signal wires. Perhaps there's some damage to that circuit or the CPS connector that is attenuating the signal. That would be consistent with it only occurring at high rpm and with the problem being worse when the air gap was opened up. I know the head needs freshening, but before I pull it I want to run a compression test and leak down test to see if more engine work is warranted. If I haven't found and fixed this problem by then I'm inclined to replace the engine harness while the head is off and it is easier to get to the harness where it runs under the intake (for grand problems, grand solutions).

03/13/2008

I found other information that says that the air gap can be .012-.028. I re-adjusted the CPS, which made no difference at all. I see a pair of fairly consistent codes after an event (misfire on cyl 6 and injector failure on both banks). The first would be a coil or coil interface problem and the latter could be a wiring or injector interface issue. But then, both could be caused by a CPS or power fault. For grins, I tried disconnecting the cylinder ID connector and saw that the DME did register that failure. It had no affect on the problem, so it would appear that the signal is valid. Likewise for the engine temp input to the DME.

I pulled the boots on "interesting connectors" to look for corrosion, but haven't found anything suspicious. I noticed that when one of these events occur that the MPG gage drives to 40mpg concurrent with the tach drop. That implies that the DME is not supplying injector pulse width info to the cluster or spark.

I think I need to find out whether the CPS signal is going away, or whether power to the DME is being interrupted. I think the check needs to be done at the DME.

03/23/2008

Power to the DME is good. I probed to wire from the code relay (ignition on signal) and the wire from the main relay (DME power) and saw normal system voltage at each. I monitored each wire with a test light (LED) while driving the car to repeat the problem. The light never flickered or dimmed during an event. Therefore I'd say power to the DME isn't an issue.

03/24/2008

I think I saw a DC level appear on the CPS signal during an event. That could be as a result of chaffed wires in engine harness. It seems a stretch that both DME's would have that fault, so the harness is now my prime suspect.

03/25/2008

I found what should be a good used harness, still wrapped around a 80k mile engine that was running great before the car it is in was rear ended. So I'm summoning the young priest, old priest, and a large jug of Bavarian holy water and swapping engines and the harness. I'm tired of screwing with this and I want to race the car at Roebling. The fresher engine should mean that I can defer the head rebuild and such and I suspect it'll make a bit more power. It will almost certainly burn less oil (a track weekend is 2-3 quarts).

04/12/2008

Work has gotten in the way of picking up the engine and harness... But I know one more item that isn't the cause. I pulled the harmonic balancer to see if its rubber mount had failed. That could cause the problem, but the harmonic balancer looks fine. No signs of cracking or separation.

5/21/2008

I finally picked up the new(er) engine and started prepping it for installation. While looking for an oil leak in the vicinity of the cooler (the leak was because the fitting was separating from the cooler) I saw that the harmonic balancer was wobbling around. For grins I swapped in the balancer from the new engine just to see what would happen. The wobble was less, but not eliminated (maybe bad front main bearings?) and that raised the cutout to around 5800rpm and made the problem less frequent. I'm onto something now...

Placing a web-cam and a headlight in the engine bay and running up to the problem area clearly showed the harmonic balancer wobbling around. More importantly I could see that the crank bolt was wobbling (worn bearings, most likely). At the point that the cut-out occurred the harmonic balancer was wobbling like crazy. I'm thinking that the wobble is disturbing the CPS signal to the point that the DME just gives up. I’ll see what happens when the new engine is in.

6/6/2008

With a prodigious expenditure of effort I got the new engine & transmission installed in time to go to Barber for a NASA event. Setting the engine on the mounts at 9am Friday morning. Only to have the shifter break too late to be able to effect a repair in time. The good news is that the harmonic balancer and crank bolt run dead true. Ah well, I did have a good weekend instructing... Note to self, don't ever let an early 911 driver trail brake. Exciting things are gonna happen!

6/14/2008

The newer engine seems to run great. I've flushed the cooling system as the car the engine came out of was an auto with a leaking tranny cooler and there was a good bit of oil in the cooling system. I've fixed the shifter and as soon as I check out the front driver side strut (the upper shock mount may be loose or worn) I'll see if it will run to the redline. I elected not to change the harness along with the engine on the premise that one should make one change at a time.

6/15/2008

Cautious optimism abounds! I've done a good dozen runs to the redline in 1st, 2nd, & 3rd without once having an "incident". Sticking a pipe on the crank bolt with the old engine mounted on my engine stand, I could detect motion in the front main bearings! That could easily explain everything.

7/7/2008

Okay the problem isn't completely solved, though I can live with it if it doesn't get worse. When trying to start on a cold engine, I have to force an immediate rev to above 2500rpm or it will die with the same sort of cut out and tach going to zero and it may experience one or more events before I see +2500rpm. It pretty much requires full throttle to accomplish that. Once I've satisfied that condition the engine idles perfectly.

On the track I see some events (at about 5500-5800rpm) until the engine is fully up to temperature, when they mostly vanish. Occasionally, once the engine is hot, I'll see a balk and tach drop on a downshift just before the clutch is engaged.

I can't think of any fault that would explain this, so I'm at a loss as to what to fiddle with. I suspect both have a related cause. I did try a third DME at the track, courtesy of another E30 owner, with no affect on the problem.

7/14/2008

Raced at CMP. While the problem is still there, it hasn't gotten any worse. The first half-dozen laps, even if I warm up the engine, are a bit dicey. One of these events in a race environment in the wrong place can be "exciting" (hint; think massive trailing throttle oversteer).

10/20/2008

I replaced the engine harness with the newer one (out of a 90 car). That required a bit of modification to match my car's configuration. I'll see how it behaves at Barber and RA.

12/15/2008

Maybe the harness was the fix. The car ran fine for both events. But with the history on this I won't be surprised if the problem comes back.

3/30/2009

Well, its back! The car ran great a CMP for three hours in the enduro and all through the weekends sessions. Then at RA it pitched a fit on Saturday in the sprint race and ran great for the enduro and on Sunday!

7/6/2009

This is weird. All through this season the cutout problem has been more or less present. The engine may act up on one day, on all three days, nor not all. Sometimes the engine just cuts out and sometimes it acts like an early rev limiter. I'm out of ideas on how to fix it. Until I get an inspiration I guess I'll have to live with it. Depending on where it happens, racing the car when it is doing this can be challenging.

Since changing the harness I've swapped in different relays, CPS, AFM, DME, ECT, etc to no affect.

3/15/2010

The 96 car was destroyed at RA in August (I had some help from a Miata driver). I've built a new car from an 88. Only the transmission, drive shaft, and engine harness were transferred over from the 87 car. I have a fresh race built engine in the car. I'm seeing the same problem as before. I installed an IQ3 in the 96 car just before it was wrecked and can see in the logs the tach signal go almost to zero for 0.2-0.3 seconds. Depending on which DME I have in the car I consistently see either a 1261 or a 1251. The problem is far worse now and can be duplicated on the street. Where before it was only happening above 5k it now occurs around 3k.

I have a spare analog input channel available and I plan to sample & log some of the DME inputs and outputs.

4/19/2010

I logged data for the DME power & ground connections, coil/injector power, and fuel pump relay control/ground/output. I saw a decline in the voltage supply to the DME with increasing rpm. Cutting the shrink wrap off of the fusible link revealed a mass of white powder and a completely corroded link. I spliced that out and installed a 60A lug type fuse in the engine bay.

Coil/injector power and power to the fuel pump relay never varied. But coincident with the cutout and rpm drop the ground to the fuel pump relay would go away. That combination strongly suggests a loss of timing data to the DME. Now to come up with a way of logging the CPS signal.

4/22/2010

I've got it! With a rented digital storage scope in the car, powered by a 1200w UPS, I can see the CPS waveform presented to the DME go wonky when an event occurs. Changing the CPS or the DME makes no difference. The wave form is generally smeared somewhat all the time. Only when it gets pretty nasty looking does the DME drop fuel relay ground and tach output. I think this means the harness is bad.

I had to repair the harness that came with this car. Some idiot "fixed" a C191 problem by splicing the wires. That meant having to cut them to get the harness off the engine. The loss from cutting out C191 and the additional loss from cutting out the splices left the harness too short. A classic case of what results from not fixing it right the first time. So I got another supposedly good used harness.

I got a harness from a wrecked 525i for free (there's little call for those). I got the engine side of C191 and enough wire to repair the harness. So now it is back to original configuration. I installed it in the car and could see a crisp waveform presented to the DME. Driving it on the street reveals no problems.

I surmise that the coax in the harness that routes the CPS data from the CPS connector to the DME has just degraded with time and heat. It is sort of interesting that the harnesses all appear to have the same problem. If I see this sort of thing again I'll cut the harness open and consider replacing the coax.

11/21/2010

Since changing the harness the car the engine has run perfectly through dyno sessions and a bunch of race & track weekends. I declare this problem solved (prematurely as it turned out!).

The lesson here is that nothing beats proper diagnostics. If I'd used a digital storage scope to log data in the beginning I'd have prevented over a year's frustration and avoided lot of work and parts costs.

Last race of 2010

Well, the problem is back. Additionally I’ve lost data from the coolant temp sensor. That strongly suggests a failing harness. After going through three used harnesses I “bit the bullet” and purchased a brand new harness from BMW. That solved all of the problems until I was forced to quit racing at the end of 2014 for a medical condition. So the bottom line is that an engine harness can’t be depended on to last forever. A used harness is something of a crap shoot, but a new harness is sure to work even though it is a pricey solution. The heat and vibration cause the internals of a harness to degrade in time. The simple act of pulling and installing a used harness can be all it takes to push that harness over the edge.
Last edited by jlevie; 09-03-2015, 12:49 PM.