94 LT1 Automatic Mis Fire & Knock, Please READ carefully, lots of info.

[boomdriver]

easy enough to pull suspect inj and connect to a pump and watch the spray. A wire that can be used to make contact can be used to "cycle" the injector to see if its late or slow to keep up.
Unless there is damage or known cause why this one inj has failed, it causes you to replace 8. Absolutely foolish to replace a single inj when all have to be accessed to get that one...may as well do 7 more for peace of mind, and because you have to do O-rings anyway,.

Good luck

 

[Hib Halverson]

So your LTFTs are lean on the left bank and rich on the right bank and #7 is dead at idle.

I know you checked fuel pressure, but I can't find in the thread what happened when you had the gauge connected and you went KOEO then off. Did the pressure hold/drop very slow or drop quickly?

 

[93Rubie]

Another Update

@Hib, it did not drop much at all. In fact I had left the gauge on overnight and the next day still had just under 20psi still in the system.

I did a leak down test on #7, is that a PITA to get that in there. Anyway I had to find TDC by turning the crank till I could hear it pushing air thru the hose then stop. Got it to stay with pressure on it and only had 4% leak down, so good hole.

Swapped #5 injector into place of 7 and vice versa. Still has dead miss at idle on #7, you can pull the plug on injector #7 no change in RPM.

Spark plug appeared to be firing as it was not carbon-ed up or fouled. I'm going to replace it for grins and giggles.

I backprobed injector #7 plug on ground PCM side. Ran my test light to positive terminal and touched the backprobe with engine running. Get faint flashes. Tried on #5 same faint flashes, so PCM is sending pulse to injector.


I have to be over looking something here, I've about had it with this POS. It has spark at the plug, plug appears to be firing. Leak down=good hole, sealing. Has injector pulse, has fuel pressure. I did pull the valve cover and VISUALLY inspect rockers and pushrods with engine running=Ok, as far as I could tell.

This pile of crap should not have a dead #7 miss by the evidence. I love how when work on cars I don't get easy crap, I get the weird WTF kinda stuff. :eyerole

All I can say is just about any other guy, mechanic, etc...would have spend thousands of $$$$ trying to fix this car and not fixed crap.

My only other idea is to do running compression test and see what I get. IDK???

I may have to just hit the reset button and start over from the beginning.

 

[G Winter]

Vacuum leak number 7 runner .. or 5 and 7 wires run parallel next to each other. IAC don't effect idle speed makes me think the vacuum leak, would make the bank lean also.
old school 5 and 7 fire in order wires should not be run next to each other ,induction can fire 7 early.

Hope I am on to something there.

 

[Schrade]

Do you have a vacuum leak? Does it lope idle when warm?

What is static fuel pressure? What EXACTLY is the leakdown time (pressure vs time).

Why replace parts blindly?

 

[93Rubie]

I'll have to check tomorrow on the possibility of a vacuum leak.
Static fuel pressure was KOEO 38psi. When pump was running 42psi.

I agree on not replacing parts, hence why I've been doing what I'm doing.

I'll have to check on the leakdown time.

 

[93Rubie]

Another Update

I'm a bit PO'ed by what I found. I took home my good HEI spark checker NOT the inline POS I was using.
Rechecked #7 for spark, it flashes the inline checker, does not produce spark with HEI spark checker. mad

Yeah, the inline is in the trash can. I wish I had better tools at home, my good stuff is at work. Needless to say, I'm getting a new HEI one for home.

Found the wires have been changed, the HACK that did it broke every wire retainer and decided to use zip ties to hold them in the their MISROUTED positions which caused them to rub on each other and metal. None rubbed through however I fully put blame on them NOT being in the proper place to be the cause of failure. #7 wire ohm'ed at 37,200. WAY too much. Limit is 30,000. It was getting spark just very weak spark. These wires and plugs where put on only 6K ago. Sad. :ugh

It is ALWAYS SOMETHING STUPID when you have issues like this and they are ALWAYS caused by other HUMANS. Dumb &*&^S!!!

The car is getting new wires, and retainers. I'm pulling the water pump it WILL be easier to get them RIGHT. Using quality plug wires I might add. :eyerole The ones on the car say United Delphi Packard Low Resistance OEM??? Not sure if this is good or bad. Evidently bad. They are NOT OEM wires. The originals on my 93 do NOT say this. They are 19 years old w/60K and still work. Wonder why?:eyerole

Lessons to be learned by all:
1. When working on cars use GOOD tools, to heck with the cheaper crap. It'll save you a headache or two or three or.....
2. Don't buy a car that has neglected and/or hack repaired, so #1 is never an issue.
3. Be smarter than I am and NOT work on someone elses hacked/POS car.
4. Fixing POS and hack jobs=ad

 

[Schrade]

Good to see you back.......Roger.

What's up there RL !


Too many folks don't want to do proper diagnostics (not this thread, but others). Someone posts, "Try replacing x part", and OPs will jump on it like a duck on a junebug. Then your stuff gets ignored.

Seems like a waste of time sometimes...

 

[93Rubie]

Finally some progess....Project car....

:eyerole Got parts and a LITTLE time....
Got the new wires on and some other things the car needed. New wire retainers and properly routed.
Started up fine, idled much better with no load. Very smooth.

Then I put it in gear, miss, ad.
Left it in gear at warm idle, parking brake on, wheels blocked, pulled #7 injector, no change in idle. ad
So on top of having a bad wire on #7, I have a bad plug too.

Oh, and the rad cap, is junk. Sucking air as the car cools down.
Also, I don't think the IAC is functional.
Doesn't matter if it is plugged in or not, car idles the same. Nice.

I got him to buy a 94 Manaul, he lost it. ad
My 93 has a different IAC setup. Any hints on how to test with out a IAC tester. Ohm the pins, what should the be? Etc...

I've fixed more crap on this car than I care to mention. Have some more to do.
I'm going to re-check spark on #7 wire with my GOOD spark tester, I better have good solid spark or I'm going to set this Corvette on fire.

My buddy bought a 5500 94 Corvette, he over paid, he got a 2500 project car.
I bought a 14K 93 Corvette, in excellent shape, even nicer now. It runs like a top....hmm....wonder why. NOT hacked AND taken care of. Imagine that!?!

 

[Schrade]

:eyerole Got parts and a LITTLE time....
Got the new wires on and some other things the car needed. New wire retainers and properly routed.
Started up fine,

COLD? Cold startup means NOTHING. Smooth idle at cold startup means nothing.

idled much better with no load. Very smooth.

Then I put it in gear, miss, ad.

What missed? Spark? Or Fuel DELIVERY?

This is where dynamic fuel pressure test comes in. Motor running, with vacuum OFF OF FPR, and also with vacuum ON FPR. When you're ready for dynamic test, post up. There's an arrticle around here which gives approximations of fuel pressure parameters for dynamic test / L98. LT1 is similar...

Left it in gear at warm idle, parking brake on, wheels blocked, pulled #7 injector, no change in idle. ad
So on top of having a bad wire on #7, I have a bad plug too.

Oh, and the rad cap, is junk. Sucking air as the car cools down.
Also, I don't think the IAC is functional.
Doesn't matter if it is plugged in or not, car idles the same. Nice.

I got him to buy a 94 Manaul, he lost it. ad
My 93 has a different IAC setup. Any hints on how to test with out a IAC tester. Ohm the pins, what should the be? Etc...

I've fixed more crap on this car than I care to mention. Have some more to do.
I'm going to re-check spark on #7 wire with my GOOD spark tester, I better have good solid spark or I'm going to set this Corvette on fire.

My buddy bought a 5500 94 Corvette, he over paid, he got a 2500 project car.
I bought a 14K 93 Corvette, in excellent shape, even nicer now. It runs like a top....hmm....wonder why. NOT hacked AND taken care of. Imagine that!?!

Why do you say IAC is broken? If there's an IAC DTC, it will say IAC CIRCUIT. Circuit means no power coming INTO the sensor, OR broken sensor, or bad ground wire from circuit to ground (with GOOD IAC).

Do you have a multimeter?

 

[93Rubie]

COLD? Cold startup means NOTHING. Smooth idle at cold startup means nothing.


What missed? Spark? Or Fuel DELIVERY?

This is where dynamic fuel pressure test comes in. Motor running, with vacuum OFF OF FPR, and also with vacuum ON FPR. When you're ready for dynamic test, post up. There's an arrticle around here which gives approximations of fuel pressure parameters for dynamic test / L98. LT1 is similar...





Why do you say IAC is broken? If there's an IAC DTC, it will say IAC CIRCUIT. Circuit means no power coming INTO the sensor, OR broken sensor, or bad ground wire from circuit to ground (with GOOD IAC).

Do you have a multimeter?

SMOOTH idle HOT no load, in park. Runs better hot, NOT cold. No miss on #7 when idling with NO load. Ran much better like that last night. I though it was fixed until I put it in drive.

Spark missing, I confirmed tonight. No spark on #7 with new wires. Checked new wire, 12Kohms. The old one on that cylinder was 37,200ohms over the limit for a good wire. I put on all new wires and retainers.

Put tester on Coil with known good wire, lots of spark when cranking, spark ok on other cylinder.
Conclusion=Coil is ok.

I've already done the fuel pressure tests, reread some of my postings. They are ok. This miss is effecting cylinder #7 ONLY.

At this point I believe I have a bad cap, ONLY logical conclusion I can see at this point. Spark getting to Rotor and Cap, Wires are good, but no spark to #7 ONLY. Given the POSSIBILITY of cross firing (remember my "pinging" from orginal postings) a bad cap could do this.

I'm more worried about the miss on #7 than the IAC, but NO IAC DTC, however, I think it MIGHT be bad based on the fact the idle does not change at all when I unplug it at idle. Also, the RPM's when the A/C kicks on do NOT go up at all just down. Also, NO flare on start-up.

Do I have a multi-meter? Does a Bear crap in the woods? (Sarcasm, good natured.)

 

[Schrade]

You've done static AND dynamic FP tests?

Dynamic FP tests are on the mag. printout posted here:


http://www.corvetteactioncenter.com...rms-up-then-no-fuel-pressure.html#post1111523

 

[93Rubie]

@Junkie, I should have mentioned it is EXTREMELY intermittent that CCM code 41. I only ever found it in history. Never current and sometimes it is there other times not. I did check the harness no obvious rubbing or chaffing.

Update:
Fuel pressure in specs at 42psi key on, pump on. Key on, pump off @ 38psi. Engine running, 38psi at idle, vacuum line off 45psi at idle. Sounds ok to me.

I did pull a fuel sample not sure how old this stuff is but I'm not sure my 1941 Farmall H would run on this stuff, very stale and hardly has any "gas" smell to it. I did put in a bit of water in my sample well see how much of it separates out. Early indicates seem it is ok, water content wise. Ethanol absorbs water last I checked.

Thinking it might be wise to drain the tank, of 10+ gallons and try some fresh 93 octane.
Fixing neglected cars really stinks on ice...:eyerole

Schrade this is the post I checked fuel pressure.

 

[93Rubie]

Finally

I found a couple hours this evening to drain the coolant out and get everything apart. I'll post a picture tomorrow of what I found.

The cap is very bad, I'm surprised the car ran at all. The rivet closest to the tip of the rotor failed and let the end of the rotor tip go forward into the "top" of the cap. This created a groove in the cap and was worst at #7 terminal. At #7 the plastic was ate away from the spark arching there. My guess a little wobble in the rotor/distortion the cap did this.

So a new cap and rotor and this LT1 should run just fine again.

This car had TWO problems a bad spark plug wire on #7 and a failed rotor which lead to a failed cap. Which affected #7 the worst.

Now I just need to get everything cleaned up and back together.

 

[Schrade]

Well, glad for ya'.

I do the boards to learn stuff. And I don't see what happened here...

"No miss on 7 with no load. Put on a load, and 7 misses."

I don't get it.

Well, glad for ya'.

NEXT? (didn't have to wait long)

 

[93Rubie]

Just to finish a thread, replaced cap and rotor. Got everything back together and fired it up. Runs smooth as silk, no missing, nothing.

Just goes to show, the Opti-spark, might be a failure, but it is not THE failure everyone makes it out to me.

Only took me 5 hours start to finish to replace the cap and rotor. Not too bad for working at home. Oh, how I NEED a lift.