An enigma insues...

[Paul Workman]

If y'all haven't gathered by now, after a long difficult surgery, the patient is having trouble in the recovery room!

It fires, but is missing badly at idle, and no change in the missing under some throttle up to 2500 rpm, except some of the missing clears up momentarily.

On fire up, there is sometimes some sharp "barking" thru the exhaust - which lead me to thinking ignition. The coils were new two years ago, and FWIW they ohm out between 5.8 to 6.2 across the posts.

The plugs were new at the time the coils were installed; platinum with 3k miles - they look "perfect". And, inspecting the plugs after a short run, I find a couple plugs that are wet with fuel, yet the plug on the opposite side of the coil are firing. And, some plugs appear dry, but fouled and a bit cooler to the touch - so I'm guessing they have been firing at least some of the time...

My pressure washer and a Honda I owned both suffered gummed ports in the carbs after storage over the winter, so my injectors came into question (reason for the earlier Accel parts# request.)

However, I got to remembering that since I run with secondary throttle plates and actuators removed, my secondary injectors come on just off idle (via the Marc Haibeck chip design), but there's no appreciable difference in the missing characteristics when throttle is added: point being it would be highly unlikely both injectors on the cylinders not firing would be equally plugged.

Injectors??? The injectors had been replaced at the time I bought the car - friend showed me the receipt for $1200+ at time of purchase. Just to check it, I ohmed them all and they checked out. So, I rigged up a pair of wires from the battery to alligator clips, clipping one clip onto one of the posts on each individual injector in turn, and with the fuel rail pressurized, I momentarily bumped the other alligator clip against the remaining injector post while looking down the IH runner to observe the individual spray pattern. All 16 injectors made a crisp "click-click" sound i.e., they didn't sound gummed up - is my point. And, the spray pattern characteristics appeared identical to the eye: marginalizing injectors as the issue, for now anyway.

The one item I changed in the interim before first turning the switch was the knock sensor - as the plastic connector piece was damaged. There are no codes, but the scanner did show only 17* advance at 1500 rpm...THAT seems a tad low, and come to think of it, the engine runs like the timing was waaay retarded (e.g., the "barking" and the sluggishness of throttle response, etc observed over the years fussing with SBCs.)

Oh, the O2s readings are a bit wacky, but they haven't had much time to heat up (burn off un-burnt fuel). Besides, it was running in open loop still and so the O2s wouldn't be having an effect in open loop anyway. The left and right integrators are both at 128.

So! Some of the plugs are fouled up now, so I'm going to replace them with some fresh ones this morning...AND reinstall the original knock sensor and see what happens to my spark advance...I'm running out of options pretty fast. Have I missed anything?

Stay tuned...

P.

PS: At times like this I am soooo thankful I cut off the coolant ports to the plenum. If I had to drain the coolant and then try to get the air pockets out each time...I'd be a little nutz by now! Now it is about a 20 minute job - if that -to pull it.

[Aurora40]

Just a thought, but you said it's unlikely the injectors would both be plugged in a cylinder. I'm not sure that matters, does it? If you supplied 1/2 the fuel needed by the air in the chamber (because one injector was clogged), would it burn? I was of the understanding that past a certain mixture, the fuel would not actually ignite as it's too dispersed (something like 15-16:1)?

But it sounds like you've ruled them out, because you've visually seen them spray properly.

Does your scanner show knock events, since you suspect the knock sensor?

[Paul Workman]

Originally Posted by Aurora40

Just a thought, but you said it's unlikely the injectors would both be plugged in a cylinder. I'm not sure that matters, does it? If you supplied 1/2 the fuel needed by the air in the chamber (because one injector was clogged), would it burn? I was of the understanding that past a certain mixture, the fuel would not actually ignite as it's too dispersed (something like 15-16:1)?

But it sounds like you've ruled them out, because you've visually seen them spray properly.

Does your scanner show knock events, since you suspect the knock sensor?

At idle the calibration operates only one injector, hence my reason to add throttle - turning on the second injector. Nada... Then later, what the hell, got the plenum off - might as well ohm out and then function test the individual injectors...Nada again.

Yes - I should have elaborated on that - by "no codes" I should have said the knock count was zero as was the knock retard. Hmmmm... Now Bob G had an issue with a replacement knock sensor, the reason I was specific about getting one for a 90, as in 91 the sensor is different. However, the GM guy said the part number I gave him was the old Delco part number and he cross-referenced it to the new AC Delco number. But, in spite of all appearances and scanner readings, I'm dubious as far as the sensor goes. Ain't gonna cost nuttin to put the old one back in and see what happens, is my thinking now. Like I said: Running out of options.

P.

[Bob G]

Where did you get the Knock Sensor

[Paul Workman]

Originally Posted by Bob G

Where did you get the Knock Sensor

Morning, Bob!

Glad you chimed in...

I got it from the local Chevy dealer. I kept the box and paperwork, "just in case" something weird (like this) happened.


P.

[Pete]

Paul ohm both the KS (knock sensor)
If plastic was broken is the reason for replacing KS i would think still good.
Also not too tight.

Good luck
Pete

[Paul Workman]

Originally Posted by Pete

Paul ohm both the KS (knock sensor)
If plastic was broken is the reason for replacing KS i would think still good.
Also not too tight.

Good luck
Pete

One (new) reads 101kΩ and the old one reads 99.8kΩ. And, there was no change at all when switching back to the old KS.

Together we've scoured the wiring issue, but nothing seems out of place - including the grounds. I'm going to check the low voltage connections on the coil packs again tonight, record a time-lapse record scan and graph it on the computer, monitor fuel pressure, and see what clues that brings. Oh, but I have this feeling something is being overlooked and how stupid I'm gonna feel when the culprit is finally found. But, at least the symptoms will be well documented - and posted here soze somebody else might benefit from "all this fun". OH! The damn thing has 3/4 of a tank of gas in it...A bit much to siphon, but I'm going to give that a try too, if all else fails. Then onto swapping ECMs? Just a thought.

P.

[XfireZ51]

With no knock counts and no knock retard, why would you suspect knock sensor? I'd ask Marc what timing curve looks like at that RPM/MAP? BTW, what
MAP/TPS readings are you getting on the scanner?

[rhipsher]

Paul is it possible that you got your plug wires crossed. I know you know what your doing but sometimes the simplest things can bite us in the azz. Just a thought my friend.

[XfireZ51]

Originally Posted by rhipsher

Paul is it possible that you got your plug wires crossed. I know you know what your doing but sometimes the simplest things can bite us in the azz. Just a thought my friend.

He's checked that several times. Not plug wires. May not be that simple.