400E Bad Misfire After Idling When Cold

[owenj99]

Hi Everyone,

I believe I have a sort of "odd" issue among the M119 ignition system. I've done a lot of looking through the forum and cannot find anything that is similar to what I am experiencing for both the 400's and 500's... Since the colder weather in Maryland has started (and even since we were in the 60 degree range a month or so ago) my 1992 400E has occasionally had this odd idle after running for a minute or two. The car will have a sudden noticeable drop in RPM followed by a pretty rough misfire that, as far as I've experienced, does not go away after driving for a few minutes. I have tried to drive through the misfire after leaving a few local stores (engine has likely been running for about a 5 or 10 minute drive, not enough to really warm everything up) to no avail. When I turn the car off and restart it, it will run perfectly again immediately after the restart, with no misfire or rough idle, when roughly 30 seconds to a minute after idling the issue will resume. The rough idle does not occur every time I drive, but i've found if I start the car, and continue driving at above idle speeds, i.e on the highway or backroads, the car will continue to run well without any issues. If it's not up to temp and I have to stop at a stop sign, stop light or leave it running in the driveway to warm up, it will sometimes start idling poorly and be low on power. Also, during this misfire, the car is very slow to rev and with it being pretty cold out now, the car appears to output more condensation and exhaust from the tailpipe compared to when it is running properly.

I have attached a link for a video file on dropbox showing the audible drop in RPM (initial RPM drop around 6 seconds into the video and the big RPM drop around 8 seconds into the video with additional engine noise shown towards the end of the video). I would just attach the video, but it is giving some kind of error for the video file not being of the file type expected, even with it being a .mp4 file. The misfire starts about 15 to 20 seconds after starting the 400 for the 2nd time tonight, followed by what appears to sound similar to a valve/lifter tap or completely missing a cylinder or two. Hard to tell due to the increased noise and lack of power. All of this occurred while just trying to run the car after being away and not running the car for about 2 or 3 weeks.

During the initial startup, after about 2 to 3 minutes of normal idling, the rough idle occurred, then I killed the car and restarted it and began the recording linked below. I cropped about 10 to 15 seconds of normal idling out the video for time and file size purposes, but it is unlike any other ignition issue that I have messed with! It is worth noting that the previous owner replaced almost all ignition components, including the distributor caps, rotors, plugs, wires, ignition coil, fuel pumps and fuel filter within the past 2 years in his ownership. All parts were replaced with OE/OEM parts with the exception of a Napa brand fuel filter. I also rebuilt the wiring harness within a few days of my ownership due to an charging issue, rough idle, lack of power/stall issue and a christmas tree of all instrument cluster lights staying illuminated while the car was running (yes, literally all), which was all related to the lower harness being fully stripped of its insulation, I guess it was the original harness. The car has roughly 124k miles on it (if that matters).

Thanks in advance for any help!

Owen


Dropbox link: 20201222_232640_1.mp4 - P.S. you are probably going to want to turn the volume up to really hear the misfire issue properly in the video!

 

[JC220]

Remove all igntion components now- inspect for moisture.

Renew the insulators behind the caps this is not mentioned above.

 

[robm.UK]

It’s not typical of a moisture related misfire problem in my view, where the engine would splutter inconsistently. Neither is it symptomatic of a fuelling issue where the misfire would tend to be more splashy.

The sudden drop in revs while idling, and the engine running normally after a restart are important pointers to another issue.

On a hunch I would check the crankshaft position sensor. Unplug coaxial connector at EZL (red arrow), clean, check that it’s not either open circuit or shorting with ohmmeter (replace if it is).
View attachment 120797

There is an ohm value for the sensor but don’t have it to hand.

Another possibility, battery voltage or alternator output. Modules require at least 11v to function correctly. Also, build up of resistance on contact terminals of modules over age can cause difficult to diagnose running issues. With ignition OFF, lift out modules, clean contacts with contact cleaner and emery paper and refit.

Do you have an OVP or base module? If you have Bosch LH-Jetronic system you presumably would have a base module. However if you have an OVP, it could be the older type which was known to cause problems. So I would suggest you renew it.

Check all fuses in box are in good shape.

With the drop in revs... hmmm... lambda control possibly could suddenly be going open loop or there is a problem with the idle recognition. There are possible reasons for both of these, but first I would check the spark plugs - looking for any fouling, which would point to an ignition issue. You could also put a probe on each of the HT wires and analyse the output on a hand held oscilloscope.

 

[gerryvz]

The @JC220 is correct. 100% this is a classic case of misfire due to ignition component problems.

You need to remove all ignition components, and inspect them carefully.

And as JC said, you also need to remove the round insulators BEHIND the rotors. These MUST be purchased new and replaced before any further diagnosis is done.

Please post photos here of: both caps (inside); both rotors; both insulators (front and rear).

While you have the insulators off the car, you should also inspect the camshaft seals for any oil leakage/seepage. Hopefully there is none at this point in time.

Would also not be a bad idea to pull all codes and reset them; then drive the car 100 miles or so and see what comes back.

P.S. There is no issue with the forum taking as an upload, an .MP4 file. The issue is the file size ... your movie is 138MB+ in size. Unfortunately, despite this forum being more generous in file sizes than about 95% of forums out there, we cannot allow file uploads of that size. If so, we would be paying HUGE amounts of money every month, just for file storage costs (we already actually are). We currently have a total of 100 GB of storage, which we are at 73% capacity of, and we are adding anywhere from 300 and 600 MB of image storage every week. If we allowed just your movie file, it would comprise around 1/3 of an entire week's storage .....

 

[owenj99]

Thanks Everyone for the help!

I have a few other projects that are a little higher up on the list to get done at the moment, but hopefully I will be able to get the parts ordered and start looking into the ignition components shortly.

@robm.UK - I am not sure what kind of module is in the 400. What are the key differences that I would need to look for to determine if the module is OVP or base? I haven't had to mess with many modules yet, luckily! I have noticed that the wire for the CPS looks to be of different material than the ones on the two 500's, so I suspect that it has been changed before, and by the looks of it, with a not very high quality item. I'll definitely be checking that for open circuit or high resistance. For the constant 11V needed, the alternator has been replaced and puts out about a steady 14.3V unloaded and about 13.9/14.0V when loaded so unless it is an internal short within the power supply to that individual component (probably the most likely) I don't think the car is having voltage issues coming from the alternator at least...

@gerryvz - Thanks for the insight into the ignition issues. I will post pictures back once I am able to move one of the other projects out of the garage for a few days to have the 400 replace it. For the video storage, I had cut the video down to about 7 seconds and lowered the quality a bit to make it just under 9 Mb when I tried to post it here, but once it gave the error with the unknown file type, I decided it would be best to just post the full length video on dropbox instead of trying to make a shorter clip work here. I completely understand the storage restrictions! Thanks for allowing us to share so many images and clips to begin with, it's just part of what makes this forum the best!

 

[gerryvz]

Thanks Everyone for the help!

I have a few other projects that are a little higher up on the list to get done at the moment, but hopefully I will be able to get the parts ordered and start looking into the ignition components shortly.

@robm.UK - I am not sure what kind of module is in the 400. What are the key differences that I would need to look for to determine if the module is OVP or base? I haven't had to mess with many modules yet, luckily! I have noticed that the wire for the CPS looks to be of different material than the ones on the two 500's, so I suspect that it has been changed before, and by the looks of it, with a not very high quality item. I'll definitely be checking that for open circuit or high resistance. For the constant 11V needed, the alternator has been replaced and puts out about a steady 14.3V unloaded and about 13.9/14.0V when loaded so unless it is an internal short within the power supply to that individual component (probably the most likely) I don't think the car is having voltage issues coming from the alternator at least...

@gerryvz - Thanks for the insight into the ignition issues. I will post pictures back once I am able to move one of the other projects out of the garage for a few days to have the 400 replace it. For the video storage, I had cut the video down to about 7 seconds and lowered the quality a bit to make it just under 9 Mb when I tried to post it here, but once it gave the error with the unknown file type, I decided it would be best to just post the full length video on dropbox instead of trying to make a shorter clip work here. I completely understand the storage restrictions! Thanks for allowing us to share so many images and clips to begin with, it's just part of what makes this forum the best!

I am not sure why you would have gotten an error, as mp4 video and audio files are explicitly allowed per the file list, which I just screen-shotted from the admin control panel.



The maximum file attachment size is 22 MB, per below.

 

[gsxr]

Best solution is uploading to YouTube, then the forum will automatically embed the video when you paste a link in a post. No size limits either.

 

[owenj99]

Hmmm. Strange. Not sure why it did that then. YouTube is a good idea that I will do next time I need to upload a new video.

Thanks again for the help and I'll keep everyone posted with pics of when I find when I get the 400 pulled apart!

 

[smilecenterlab]

i had the same problem with my 500e ,after replacing caps,rotors and insulators problem solved.

 

[robm.UK]

@robm.UK - I am not sure what kind of module is in the 400. What are the key differences that I would need to look for to determine if the module is OVP or base? I haven't had to mess with many modules yet, luckily! I have noticed that the wire for the CPS looks to be of different material than the ones on the two 500's, so I suspect that it has been changed before, and by the looks of it, with a not very high quality item. I'll definitely be checking that for open circuit or high resistance. For the constant 11V needed, the alternator has been replaced and puts out about a steady 14.3V unloaded and about 13.9/14.0V when loaded so unless it is an internal short within the power supply to that individual component (probably the most likely) I don't think the car is having voltage issues coming from the alternator at least...

If you have an OVP it would be in front of the main fuse box. There would be a few square relays near it. It would have a flip up (usually clear) plastic cover and a single 10A (red) fuse.

The base module is a silver box with black top held on by 4 allen head screws to the left of the engine with three 10A fuses.

Definitely check out the CPS.

It is interesting that Honch and @JC220 are confident that you should be replacing ignition parts. I would advocate appropriate diagnosis first to confirm an ignition misfire before removing or replacing ignition parts, unless I am 100% confident of the cause of the problem, but it is rarely the latter when diagnosing over the internet. A scope would confirm whether it is an ignition related misfire or not.

The sudden drop in revs while idling, and the engine running normally after a restart are not tell tale symptoms of moisture related misfire.

I mentioned an open loop scenario. If your engine goes open loop, say because of an intermittent faulty O2 sensor, the engine revs would drop and engine would run rough. Normally lambda control should be closed loop and the ECU adjusts fuelling according to O2 sensor signal, amongst other sensors. Your 400e should have self diagnosis capability and to this end there should be a diagnostic connector (x11) on the left fender. Using your multimeter set to read duty cycle (-ve probe to pin #2, +ve probe to pin #3) you should be able to monitor the off-on ratio of the closed loop operation while the engine is running. In a correctly functioning system the reading should fluctuate around 50% +/-20%. Alternatively measure voltage between these two pins. The voltage should fluctuate around 50% of battery voltage.

The self diagnosis feature is a powerful tool in diagnosing fuel system problems.

You can also check the lambda control by monitoring the O2 signal using Star if you have this software.

Another thought occurred to me. A build up of back pressure. Do you get a sulphur/rotten egg smell while driving, or have you noticed more heat than usual in the cabin around the transmission tunnel?

 

[Kyiv]

If you have an OVP it would be in front of the main fuse box.

No OVP on 400E/500E

 

[robm.UK]

Yup, thought so but wasn’t sure. Thanks

 

[owenj99]

@robm.UK Interestingly enough, I had wondered about the clogged cat / O2 issue as well. I encountered a similar issue with the C32 where one catalytic converter was clogged and restricted flow so much that it will actually deactivate a whole bank of the engine. Started with similar symptoms after an O2 sensor failed and caused the car to run extremely rich.

As for the sulfur smell, I havent noticed anything and honestly havent really driven the car enough since purchasing it to notice the trans tunnel getting warm. I will try and take the car for a drive this evening as I will need to drive almost an hour round trip and see if I notice any smells or heat coming from the tunnel.

Unfortunately, no star diag for me not saying that it couldn't be ignition related, but the abrupt drop in rpms and it working immediately after restart seemed to be more of an electronic or sensor issue and not so much of an ignition component issue, but I could totally be wrong...

 

[robm.UK]

Just an observation of the video. The revs at 10+ secs into the video look to be around 750rpm, which is near to the normal 780.

When the engine is cold, the cold start feature operates open loop and automatically raises the revs to 900rpm up to 30 secs depending on coolant temp, which according to temp gauge in video looks to be stone cold.

So the change in revs that you detected as a drop in the video could be the fuel management trying to go into closed loop function, but there may be a problem causing the system to stay in open loop. Say a faulty sensor?

 

[owenj99]

So the car was running for about 2 minutes and then it started to run rough, after which I restarted the car and started recording the video and after about 15 or 20 seconds it started running rough as shown in the video. Engine was still cold, but was past the 30 second or so high idle period.

I think something is up the the gauge because it takes a long time to warm up (probably 20+ minutes) and never really goes above the 80 mark. I replaced the thermostat, flushed coolant and changed the temp sensor for the gauge...

 

[nocfn]

Has the upper harness been replaced? (checking for wire issue)
Have you changed out the three sensors on the manifold? (they are at least 26 years old and do wear out)
Glad you changed Tstat.
Have you physically checked each of the vacuum connections for leaks.

Still think that the ignition system as mentioned is the problem with the rough idle.

 

[gsxr]

I think something is up the the gauge because it takes a long time to warm up (probably 20+ minutes) and never really goes above the 80 mark. I replaced the thermostat, flushed coolant and changed the temp sensor for the gauge...

Could be a faulty gauge, but you can also measure resistance at the 4-pin temp sensor (and 2-pin) and see if the resistance charts all indicate simlar temperatures. If they are showing ~80C when warm and your gauge is still below 80, the gauge or wiring is suspect.

Star SDS is another easy way to check, if you have that available. This will show temps from the 4-pin sensor.

 

[owenj99]

The gauge seems to read fairly accurately compared to actual coolant temp. With my IR thermometer, when the thermostat area is reading about 80°C, the gauge is reading probably somewhere between 73 to 75°C. I guess I should have been more clear in my explanation as it just takes forever to get to temp, even with the new t-stat.

As for the upper harness I am not sure. The wiring to the cam solenoids looks to be in great shape with no tearing or degradation of the insulation. The wiring in the loom running along the intake manifold also looks to be in good shape. The car was previously owned by an older couple that did a bunch of maintenance at indy shops in the Orlando area, but the service records are not very descriptive. I had to Repair a ground to the top rear area of the intake manifold that appeared to be chewed by something, but that was the only damage that I have noticed. Also, many of the vacuum connections and lines were replaced by the previous owner, but I haven't tested them.

 

[gerryvz]

A properly working thermostat, even in very cold ambient temperatures, should only take a few miles / minutes to get to working temperature, and on an M119 should be reading just above the 80C hash, up to 90C. That would be the proper range. If things are reading below 80C after the car has been run for a few miles, then something is wrong and requires further diagnosis.

 

[gsxr]

Also check the harness for modifications. It's unlikely, but worth a look.

Years ago, one of my cars was reading abnormally low temps, vs what the HHT was displaying from the 4-pin sensor. Eventually I found out a creative indy shop had wired a resistor in series with the dash gauge sensor, to artificially lower the indicated temperature. This was after the shop was unsuccessful in curing a persistent hot-running complaint by the PO. After the PO returned multiple times complaining, they made the gauge read lower and he was happy.

 

[nocfn]

Faceplant is right!

 

[robm.UK]

So the car was running for about 2 minutes and then it started to run rough, after which I restarted the car and started recording the video and after about 15 or 20 seconds it started running rough as shown in the video. Engine was still cold, but was past the 30 second or so high idle period.

The timing fits with the KE system trying to go into closed loop operation.

During warm up the idle speed is elevated up to a maximum of 30 secs, but the KE system can also operate open loop for up to 2 mins maximum during which time the cold start valve is in operation. After a restart the elevated idle speed function is inhibited for 20 mins, but the cold start features of the warm up system can still operate for up to 2 mins depending on coolant and ambient temperature.

The @robm.UK hypothesis (hunch): -

So, what happened in your case is, I believe - you start the car for first time from cold. It runs through the high idle phase, probably for 25 secs or so, but continues in normal warm up open loop phase for up to roughly 2 mins after start, during which time the cold start valve is operating. You would not necessarily detect a change in revs, albeit they would drop very slowly during this 2 min period. After which the KE management system tries to go into closed loop function. But there is a problem with a KE system sensor (4 pin temperature sensor, O2 sensor..?) and the KE system is forced to operate cold engine (not properly warmed up after 2 min idle) on emergency running parameters, resulting in poor idle and rough running.

You stop engine and restart. After restart the KE system inhibits high idle phase for 20 mins. So this time engine operates initially in normal warm up (open loop) phase. But since engine had been running previously for 2 mins, the KE warm up phase is much shorter this time, not 2 mins but more like 10 to 15 secs. After this point the KE system tries to go into closed loop function, but there is a problem with a KE system sensor, resulting in bad idle.

Of course there could be more than one issue.

 

[JC220]

Except the 124s have a completely different LH fuel injection system

 

[gsxr]

@JC220 is correct. The KE (CIS/CIS-E) mechanical systems are not even on the same planet as the LH-SFI electronic injection. There is a huge amount of real-time live data visible on a digital scanner (i.e, SDS with HHT-Win) to help diagnose LH systems.

BTW, @owenj99 , for your temp gauge troubleshooting... at operating temp, measure the resistance at the sensor on the manifold, then also measure the resistance at the connector behind the cluster. They should be very close. Use the chart below to see if the numbers match. 80°C should measure somewhere near 75 ohms, give or take a couple percent. I need to check this on a hot engine to confirm the chart is accurate, but I trust Jeremy's work:

 

[robm.UK]

Yes, you are right. LH not same as KE. Thank you for pointing out my error. I apologise to OP. My description of the warm up phase, whilst correct for KE, is incorrect for LH-SFI, where the start control function in the LH-SFI ECU provides air/fuel mixture adjustment dependent on the engine coolant temperature (CTS) and achieves this by increasing the duration of the injection. Warm up adjustment stops when the engine is at operating temperature, and is not time dependent like KE.

However, there should be an X11 diagnostic socket on the left inner fender, which allows powerful diagnostics with a simple multimeter without STAR by measuring the off-on ratio. The x11 socket was remove around June 1993.

The 4 pin CTS would be worth checking, but they’re so cheap it’s often easier/quicker just to replace.