× Help us help you. By posting the year, make, model and engine near the beginning of your help request, followed by the symptoms (no start, high idle, misfire etc.) Along with any prevalent Diagnostic Trouble Codes, aka DTCs, other forum members will be able to help you get to a solution more quickly and easily!

Jeep Wrangler 4.0 secondary ignition waveform

  • Rutesic
  • Topic Author
  • Offline
  • Junior Member
  • Junior Member
More
10 Mar 2020 17:46 - 10 Mar 2020 17:57 #38226 by Rutesic
Hi all,

I'm tracing some idle misfire on my Wrangler 1995. 4.0 automatic. Engine shakes a bit but I can't find out why. It is not constant like when I unplug injector from a single cylinder, it is more like random cylinders misfiring. Distributor, coil and wires are as per FSM and have only 4-5 thousand miles on them. Cap, rotor and plugs are brand new. I had some issues with crank sensor signal and I've finally managed to get it to a decent shape.

I need some help regarding secondary ignition waveform interpretation. Is the waveform from video below ok? I can see some weird peaks at the end of burn line, sometimes it is longer than 2ms, and firing voltage is sometimes as low as 6kV. Video is slowed down (you can slow it down further on youtube) and it shows all cylinders (153624 firing order). I don't have another probe to use it as a single cylinder trigger. Time scale is 1ms while voltage is set to 2kV.

Last edit: 10 Mar 2020 17:57 by Rutesic.

Please Log in or Create an account to join the conversation.

  • Rutesic
  • Topic Author
  • Offline
  • Junior Member
  • Junior Member
More
10 Mar 2020 17:50 - 10 Mar 2020 17:57 #38227 by Rutesic
Replied by Rutesic on topic Jeep Wrangler 4.0 secondary ignition waveform
Here is the sample. I'm not sure if this is something scope related or it is really like that... Scales are 1ms and 2kV



I have just seen that CPS signal is not ideal yet. Cam/Crank relation should be different, it seems like the crank signal is a bit moved to the left. I'm wondering if cam/crank out of sync and this longer second pulse on crank signal would cause misfire?



CPS scale is 10ms 5v
Attachments:
Last edit: 10 Mar 2020 17:57 by Rutesic.

Please Log in or Create an account to join the conversation.

More
10 Mar 2020 23:55 #38242 by scannerjohn
Replied by scannerjohn on topic Jeep Wrangler 4.0 secondary ignition waveform
spark firing voltage should be under 20kv. spark burn voltage 1.3 to 4kv (under 6kv). spark burn time 1.5ms no less then .9 or more than 2.4ms. 2ms can be Ok. end of spark is turbulence can be lean condition.

cam crank out slightly... should be 50% at turn on-off.


The following user(s) said Thank You: Rutesic

Please Log in or Create an account to join the conversation.

More
11 Mar 2020 09:59 #38247 by chief eaglebear
Replied by chief eaglebear on topic Jeep Wrangler 4.0 secondary ignition waveform
Hi sir not a lot of experience here that waveform does seem to be stretched out a bit I did not see an injector pintle hump and also that turn off oscillation looks funny where does ignition module get it s ground seems like spark line is a bit weak
The following user(s) said Thank You: Rutesic

Please Log in or Create an account to join the conversation.

More
11 Mar 2020 11:08 #38249 by John Curtis
Replied by John Curtis on topic Jeep Wrangler 4.0 secondary ignition waveform
Doesn’t look like a spark problem.

Here’s some things to keep in mind.
ANYTHING that can slow the revolution if the engine can create a misfire. Any pulleys, a harmonic balancer shifting wobbling.

I don’t really feel it’s necessary to ask for current ramp. I do think you should scope spark and spark control. Also a relative compression test and secondary ignition as a sync (timing).

Thinking out loud always helps me in the process.

Please Log in or Create an account to join the conversation.

  • Rutesic
  • Topic Author
  • Offline
  • Junior Member
  • Junior Member
More
11 Mar 2020 11:45 #38250 by Rutesic
Replied by Rutesic on topic Jeep Wrangler 4.0 secondary ignition waveform
Thank you!

John Curtis wrote: I do think you should scope spark and spark control.

Sorry but I don't understand what exactly should I scope here? Compare firing events to cam/crank sensor readings?

John Curtis wrote: Also a relative compression test and secondary ignition as a sync (timing).


This engine was rebuilt 3k miles ago. As for the compression, I did test compression check with gauge and it was 150 -/+5 psi. Factory asks for 120-150psi. Considering this I guess there is no problem with intake valves or rings. But this test does not verify exaust valve condition (eg. if they open properly due to worn cam lobes). Could I verify this with relative compression test?

Please Log in or Create an account to join the conversation.

More
11 Mar 2020 12:01 #38251 by John Curtis
Replied by John Curtis on topic Jeep Wrangler 4.0 secondary ignition waveform
You want to compare firing time with TDC using relative compression and ignition.

Thinking out loud always helps me in the process.

Please Log in or Create an account to join the conversation.

  • Rutesic
  • Topic Author
  • Offline
  • Junior Member
  • Junior Member
More
11 Mar 2020 12:43 #38252 by Rutesic
Replied by Rutesic on topic Jeep Wrangler 4.0 secondary ignition waveform

John Curtis wrote: You want to compare firing time with TDC using relative compression and ignition.


Will do, thank you. Regarding lean condition, do waveforms from that first video look like a little lean condition? I'm afraid if I have intake vacuum leak somewhere

Please Log in or Create an account to join the conversation.

More
11 Mar 2020 13:35 #38254 by John Curtis
Replied by John Curtis on topic Jeep Wrangler 4.0 secondary ignition waveform

Rutesic wrote:

John Curtis wrote: You want to compare firing time with TDC using relative compression and ignition.


Will do, thank you. Regarding lean condition, do waveforms from that first video look like a little lean condition? I'm afraid if I have intake vacuum leak somewhere


I can definitely see how ScannerJohn is thinking that with the end of spark line but I think it may be okay but am not 100% positive. ScannerJohn may be positive and may be able to explain why it is lean (teaching us both). The end of spark to me looks like a typical ignition waveform, if it was drastically higher I would say for sure it is a lean issue. Personally I would use other data to help draw that conclusion since I am unsure of the waveform.

Try spraying some water all around your intake manifold and see if if the engine bogs down.

As far as intake valves, if you have a pressure transducer you would be able to see a valve problem. If you don’t, they’re pretty expensive and the next best thing might be to use a vacuum gauge. Valve train problems can cause at idle misfires that get better with RPM increase.

Thinking out loud always helps me in the process.

Please Log in or Create an account to join the conversation.

More
11 Mar 2020 16:12 #38259 by Andy.MacFadyen
Replied by Andy.MacFadyen on topic Jeep Wrangler 4.0 secondary ignition waveform
Looks okay to me, not every firing stroke is identical and the fuel-air ratio is continuously changing in response to the O2 sensor. Also with distributor ignition systems individual aren't as repeatable as with coil on plug. From.your description I would want to double check the valve clearances, too narrow a clearance often won't show on a compression test.

" We're trying to plug a hole in the universe, what are you doing ?. "
(Walter Bishop Fringe TV show)



Please Log in or Create an account to join the conversation.

More
11 Mar 2020 17:02 - 11 Mar 2020 17:04 #38261 by scannerjohn
Replied by scannerjohn on topic Jeep Wrangler 4.0 secondary ignition waveform
Should have a slight rise in the burn line at the end which is left over energy from the coil at the end of the spark. When the tail raises up as in several of the waves, this indicates that all the hydrocarbons have been burned leaving high resistance in the cylinder, a lean condition.
If its in only one cylinder check for leak at intake runner of that cylinder. If its all check for lean variables for a global lean.
The burn line looks pretty good, should be flat. As you can see, it has a slight rise when you have the spike at the tail. The spark fire voltage will rise high as well.
If you view the waveforms in a parade view you can compare each and if you can isolate #1 cylinder you can see which of the cylinder are having problems. Looks a little erratic.

Ignition waveform analysis is some heavy stuff but it gives a lot of insight. I'm still learning and studying.

I'm thinking you have a lean and ignition timing problems.


Last edit: 11 Mar 2020 17:04 by scannerjohn.

Please Log in or Create an account to join the conversation.

More
11 Mar 2020 17:33 #38262 by Tutti57
Replied by Tutti57 on topic Jeep Wrangler 4.0 secondary ignition waveform
If you suspect an intake leak you can scope your o2 sensors and use propane or another fuel source around the engine while you watch for a high voltage trace when it sucks in the fuel.

Nissan Technician

Please Log in or Create an account to join the conversation.

  • Rutesic
  • Topic Author
  • Offline
  • Junior Member
  • Junior Member
More
11 Mar 2020 17:58 - 11 Mar 2020 17:58 #38264 by Rutesic
Replied by Rutesic on topic Jeep Wrangler 4.0 secondary ignition waveform
Thank you all for tips.

Fuel trim is around +3% most of the time. Ok, so next step is to verify ignition timing and check for intake leaks.

I don't have pressure transducer. However, should I be able to check individual cylinders by doing dynamic (running) compression test with gauge? If I understand well that would show me if intake and exhaust valves are opening/sealing properly
Last edit: 11 Mar 2020 17:58 by Rutesic.

Please Log in or Create an account to join the conversation.

More
11 Mar 2020 21:10 #38275 by John Curtis
Replied by John Curtis on topic Jeep Wrangler 4.0 secondary ignition waveform

Rutesic wrote: Thank you all for tips.

Fuel trim is around +3% most of the time. Ok, so next step is to verify ignition timing and check for intake leaks.

I don't have pressure transducer. However, should I be able to check individual cylinders by doingcompression test with gauge? If I understand well that would show me if intake and exhaust valves are opening/sealing properly


When I’m dealing with drive ability problems and looking at fuel trims 10 is usually the safe number, however 6 is my tolerance for problem vehicles.

You’re going to want to do a leak down test. It’s different than compression testing in that you use a compressor to pressurize and it will show the amount of leak-down. You’ll have to figure out where it’s escaping from by listening to the exhaust, removing the oil cap, radiator cap or coolant reservoir, or air intake/throttle body.

Thinking out loud always helps me in the process.

Please Log in or Create an account to join the conversation.

  • Rutesic
  • Topic Author
  • Offline
  • Junior Member
  • Junior Member
More
12 Mar 2020 15:21 #38289 by Rutesic
Replied by Rutesic on topic Jeep Wrangler 4.0 secondary ignition waveform
Thank you guys for all your suggestions. I will check engine with leak down test and maybe running compression test and see if the cause for the misfire is mechanical.

If not, I assume there are four options:
1. Ignition ( considering your responses there should not be any issues with this part)
2. Fuel delivery/injectors ( fuel pressure is around 30psi idle which is 1 psi below Chrysler spec)
3. Air leaks ( since fuel trim is 3% it should not be anything major)
4. Something sensor/ECU related

What bothers me are timing events. There is one pulse in crank signal that is a bit wider that all others. Could this one mess up spark/fuel timing enough to cause random engine shakes ?

Please Log in or Create an account to join the conversation.

  • Rutesic
  • Topic Author
  • Offline
  • Junior Member
  • Junior Member
More
14 Mar 2020 18:12 #38359 by Rutesic
Replied by Rutesic on topic Jeep Wrangler 4.0 secondary ignition waveform
Ok, so I tested all the cylinders and they seal perfectly. I also did compression test one more time - 150 to 155 psi on all of them. Based on this I don't think that something mechanical is causing misfire.

I don't have current clamp so I cranked the engine and scoped crank sensor and secondary lead. It seems that spark occurs between 3rd and 4th peak of each crank sensor signal group. There are no missing sparks or more than one spark per cylinder, so this seems to be consistent.

After that I took fuel pressure gauge and measured pressure on idle. This time it had 27-8 PSI on idle. Factory spec is 31 psi. If I snap throttle it will bounce up a bit - maybe 2-3 psi, and when I release throttle it would go to 26 and then climb to 27-8. Is this proper behavior?

I have also tried to sync cam/crank sensor, but it is impossible to do so with this distributor. I followed FSM - put harmonic balancer to TDC (0 mark), blocked distributor shaft from rotating with a pin, however when I put it back i can't screw it in - i need to remove pin and rotate it a couple of degrees. This is weird, only thing that comes to my mind is that the clamping slot is not correct on distributor or that harmonic balancer does not point to TDC properly.

Please Log in or Create an account to join the conversation.

More
14 Mar 2020 19:58 - 14 Mar 2020 20:03 #38365 by scannerjohn
Replied by scannerjohn on topic Jeep Wrangler 4.0 secondary ignition waveform
fuel pressure is off... 28-31 idle. On snap throttle should go up about 10lbs then drop to 26 is Ok then returns to 28-31. Pull the vacuum hose at the pressure regulator. Pressure should increase to 40-42psi. If not, check for vacuum.

I looked at your secondary waveform... check for carbon tracking on the plugs and or plug boot. Also check to make sure EGR is closing all the way. Those waves are erratic, should be all the same. I sure would like to see the secondary in a parade form of all...


Last edit: 14 Mar 2020 20:03 by scannerjohn.

Please Log in or Create an account to join the conversation.

  • Not Allowed: to create new topic.
  • Not Allowed: to reply.
  • Not Allowed: to add attachements.
  • Not Allowed: to edit your message.
Time to create page: 0.387 seconds