4x4jeepmanthing

I put the fuel pump relay back and put the plugs back in. I took a ground and hovered it near the ignition coil secondary cable that connects to the distributor, screwdriver hanging out. I couldn't get it to arc off the engine, so I ran a groundwire from the battery close. We have spark, blue/orange. We also have wet plugs! I am now quite perplexed and it's time for bed.

Dave51

I always love your threads! They're always like the most interesting ever!

You got any engine codes while all this is going on?

First confirm the compression. Borrow another tester, get one at HFT or wherever, or if you have an air compressor with a reasonably accurate gauge MacGyver something up (bicycle tube or tire valve or whatever fits) to test the gauge you have for accuracy.

If you want to continue to make waveforms (which may or may not be helpful) get an HT-201 attenuator (at least for ignition. You might just get under the wire for the injectors). Measure all 6 things-- don't assume that because one thing is doing something they all are.

That certainly implies a sudden failure, and although the compression is (probably) bad, it didn't get bad in the parking lot.

Has it been like really cold there all the time you've been trying to start this? Throw some starting fluid in there and see if it will start (a low compression engine should start. AAMOF I've started and driven a car with -0- compression (Honda interference engine that jumped the timing chain and got interfered with)(OK it took a LOT of effort to get it started and didn't run all that hot when it did start).

If it does start then do the "steam cleaning".

If (when) it don't, then you gotta think major timing disruption, like a jumped chain (yes, you can jump a 4.0 chain. Not easy, but it can be done).

Fortunately, a scope will identify that:






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Dave51

I anticipate your next question will be

Well, that's where things get a little cloudy..

4x4jeepmanthing

Oh how I wish my thread could be boring and the smoking gun was obvious after testing the cam/crank signals. I tested for spark at least 5 times and then before calling it, I shut of the headlamp, low and behold after the ground wire was brought near, spark. Embarrassing
I'll pickup the attenuation if that will keep us on track to pin point what is going on here. The artifact on the cam did not sit write with me, after you brought it up again, I had to try verifying again, my apologies for what has turned into a full circle of spark.
I will certainly be re testing compression!

4x4jeepmanthing

I Can guess at settings, if you have a wiser starting point i would prefer to start with that, as i clearly do not know what I am doing with a scope. Do tell please?

Dave51

Attenuators are cheap, and get a spark tester, also cheap. Perhaps the spark is weak and needs to be looked at a little closer.

The 20:1 attenuator plus the 10x probe should allow using spark for the scannerdanner test (I hope)(it'll be close).

You could also borrow my unit (with postage and a massive security deposit of course). The current clamp and HT-25 ignition probe makes life a heckuva lot easier.

OTOH start yanking stuff-- pull distributor and timing cover and look for damage.

How about CEL codes?

Dave51

Nah, you got this. As long as you don't smoke the unit, everything else is turn it up or turn it down until you get a good image.

Dave51

Ooops.

Short version: You can't do the scannerdanner relative compression test.

Dave51

Maybe probably anyways.

Long version.

I went out and got set up to get a screenshot of all the settings to do the test:



and get the settings (sorta). Now I have to set up differently from you cause I have COP and it's a PIA to measure individual ignition signals. You have to take off the coil rail, get some spark plugs wires, tie the rail back to the block, and then shazam use the HT-25 cable to measure current. Current- this is going to be important in a minute.

With the COP system tho, you can measure current (there it is again) from the coil drivers (see the CC-65 in the back of the engine) and be able to do the scannerdanner test. You won't know what cylinder is firing but don't need to know that.

Anyway...

So now I go to hook up to the battery and... you can't. Because you have to measure current and my CC-65 is stuck in the back of the engine (HT-25 might work, more on that later).

So in your case it's on to Plan B-- wire wrap for both measurements. Note how many turns you use, this could be a good reference for other DIYers.

Dave51

There is that teeny, tiny concern. We're talking a lot amps here now, and your unit may be very limited to what you can throw in there.

Dave51

I mean, if 5 volts = 8 amps, I'm kinda thinking we're limited in our application here.

And if I understand the wire wrap trick (and please correct me if I am in err) more wraps (and wire diameter) increase amperage. Therefore, I'm a little skittish when I see the 770CCA label on the battery.

4x4jeepmanthing

I'm looking these up,
The current clamp is the HT-25 isn't it?

Dave51

Current clamps are either CC-65 or CC-650. HT-25 clips on a plug wire for measurements.

HT-201 attenuator should provide the protection needed if you want to Rube something up.

In re: CEL also note if ASD was out for less than 2 restarts (or we can weed that out).

Specifically, looking for stuff like "Your PCM Is Fried".

4x4jeepmanthing

I'll order an attenuator if that just leaves the CC and ht-25 as luxury items?
As for scanning for codes, it was done before towing and nothing showed up other than for pulling out the fuel pump relay. I can scan again after work and see if anything has shown up. Thus far there has never been a CEL. I shall look into another compression gauge.

Dave51

CC-65/CC650 and HT-25 would be most appropriately be termed "Essential Items".

HT-201 Attenuator should provide protection for "****ing around".