Calling all you Diagnostic Gurus | SOLVED Stumbling on hard acceleration THANKS EVERYONE (1 Viewer)

SmokingRocks

I bought a Cruiser to keep miles off my Cruiser
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At this stage, i would check the Catalytic Converter and make sure is not clogged up.

Vac gauge shows a slight vacuum at redline which indicates the exhaust is flowing fine. There is no downstream o2 sensor on the 93-94 so other than causing massive back pressure there's really no impact those could have. If there was massive backpressure the vac gauge would read 0 in at WOT redline and the engine would struggle up top, none of which is happening. What made you think of the cats?
 

SmokingRocks

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Ok so I unplugged both O2 sensors to force it to run in open loop and the hesitation is gone. So this confirms a sensor issue and rules out mechanical and wiring issues.

so the physical things are fine. Replacing my o2 sensors tonight.


Spoke too soon, it’s still there. So I’ve got to check the mechanicals and wiring.
 
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SmokingRocks

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Unplugged the knock sensors and the stutter was more noticeable.
 

SmokingRocks

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Ohm'd the spark plugs again, all were between 4.1-4.8 ohms. Did a compression test with my oscilloscope and it looks like the engine is making good compression. Videos below for the symptom (you can hear it more than you can see it, and the compression test.


compression check
2DC710BC-8824-49C3-8512-DB5CA90A648A.png

while driving

F8CE7E08-1C21-4219-A603-C9401357B8D3.jpeg
 
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SmokingRocks

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Did my water pump and gasket tonight and I O-scoped the + to the ignition coil to make 100% sure it's not on the ignition side, here's the video of me doing a pull from idle to 3800rpm with hesitations. So the Oscope data log looks good, tomorrow I dive into the fuel side. (You can play this on half or 1/4 speed to see that there is never a drop in the demand for spark)

 

SmokingRocks

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Can you Scope the secondary?
What secondary?

Have you checked the fuel pressure?
No, I swapped the fuel pump with my spare and the problem persisted. If it were low fuel pressure wouldn't it run out of steam up at the top of the rev range?

Have you checked the air boot for cracks?
Yes, it's fine, no major vac leaks at idle.

What kind of air filter do you have?
OEM, ran it with the air cleaner open (unfiltered air) the other day when I tested out Bens AFM and the hesitation was still there.

When you remove the valve cover cap or lift the oil dipstick do you see a change in the idol?
yes
 
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If I read that right you said you did coil positive that's primary ignition. Secondary ignition is taken at spark plug wire, Do you have a secondary ignition adapter for your scope. It looks exactly like the timing gun where you clip on to the spark plug wire. I know you said you cleaned up the grounds and what not, have you checked voltage drop at the engine?
Next I would check for voltage and ground at every sensor making sure there is no voltage drop anywhere else.
I know you tried another one but you should scope out AFM on a test drive to make sure there's no drop out on it.
In case you are not aware you can test everything at the computer if you drop down the glove box and unbolt the computer.
Easier to use your scope.
 
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SmokingRocks

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I don't have a current clamp for my homemade oscilloscope, although I wonder if I can just probe my pickup for my timing light... hmmm. I'll check the voltage drop.

Yea I know about testing at the ECU, I'm going to test the injector signals at the ecu tonight.
 
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You can wrap a wire around your coil wire and use it as an inductive pickup for your spark. Try 10 wraps, hook one end of wire to your probe ground and the other to your scope probe center. I'd probably ground the ground end to chassis so you don't have to change your name to smoking scope...
I'd the signal is too small, add more wraps.
You might be able to see if it's dropping sparks this way.
 

SmokingRocks

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Omg I think I found it!

Here is a video of me O-scoping the control side of the fuel injector circuit for Cylinder #4 at the ECU. Same was noticed on Cylinder #6. More to come
 

SmokingRocks

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So here's what I found and I believe its telling me there is a wiring issue between the ecu and the injectors causing them to ground at incorrect times. Does my logic check out?

The image below was taken of a time when the engine was accelerating normally.
oscope Page 001.jpg



This image is of a time when it stuttered. See what's wrong here? I saw this on Cylinder #4 & #6, I stopped scoping after that.
oscope Page 002.jpg
 

SmokingRocks

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How's the harness around the EGR?

When I did my rebuild I rerouted the harness to avoid the EGR so it was well clear. Unfortunately, this also meant the harness did some sharp 90* and 180* bends at the firewall to get up and behind the heater mixing valve. Which probably hasn't been a great condition for the wires. I should have a spare harness in my bins unless I hacked it up to replace connectors. I'm taking off the intake manifold to get access to the harness, if there is a break I'll fix it, otherwise, I might just run 6 new signal wires to get me by until I can get a replacement harness since I have an off-roading road trip scheduled on new years.
 
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Do you have access to the ohm values?
Any aftermarket accessories that might be interfering?
Lap scope the distributor sensors RPM Etc.
Also at the computer check all the powers and grounds make sure that they're not off.
 

SmokingRocks

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Since I didn’t check current I can’t confirm if the ground that is firing the injectors at the wrong time is coming through the ecu or a short. I’m suspecting a short but the test you are suggesting I complete highlights a valid concern.

Is the ecu being told to trigger the injectors at the wrong time or is it truly a short condition?

it would seem like the easiest way to confirm or rule this out would be to use the oscilloscope to test current flow at the injector control wire. If the extra injector pulse is triggered and there is no current through the ecu control wire then I’m looking at a short, if there is current in the wire during the extra pulse then something is telling the ecu to fire the injector at the wrong time.
 

SmokingRocks

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that being said ^.
I have a hard time believing the ECU would short fire an injector like this randomly even if it was being tricked to by a sensor and not throw a CEL.

so I’m going to continue to focus on the wiring harness. I might go ahead and replace the injectors just because I’m there.
 

SmokingRocks

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In case anyone is wondering what oscilloscope I’m using it’s a home made bit that I put together when I did my custom gauges.

It may not be pretty but for under $15 it gets the job done. And it’s super easy to upload data logs to the interwebs.
2F07CF6C-948C-4FBE-8D8E-004868793916.jpeg

0337CC52-0A80-4E19-846E-D23B9D534A4D.jpeg
 

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