Prior to this morning, I was getting a crank/no start condition after I had bypassed the vats key resistor.

This morning I disconnected the #3 injector plug and attached the "noid" light to the plug. (I chose #3 for its convenient location and ease of visibility for the noid light).

I cranked the engine and the noid light illuminated in a pattern consistent with the injector receiving the pulses.

BUT: The engine started and ran on the remaining 7 cylinders. An INTERESTING development!!

This obviously means the 7 other injectors were sending fuel as required. Aside from the normal miss on cylinder #3, the engine ran smoothly. After shutting the engine down, I checked the resistance of injector #3 and noted 14 ohms. This is consistent with the two more I checked (+/- .2 ohms) on the same bank. A nominal reading.

So, on a hunch, I plugged #3 back in and attempted to start the engine. The results were the same as it was prior to this morning. The "Crank, but no start" condition reappeared.

I'm sure some of you must have encounted this phenomenon before and perhaps can shed some light on what's going on here.
1. What does the FSM say about this?
2. What would be the next thing you would check?

 

Are you glad you did the noid light test before you pulled the bread loaf to attack the VATS?

To be perfectly clear - which fuel injector(s) (brand/model) are currently installed in the engine?

Didn't you just replace these injectors or have them serviced - who sold you these or who did that rebuild work?

Your ECM is a "batch fire" (all 8 fire at once) setup so more than likely your issue is the sum of all the injector coil resistances across the coil are too low.....it sure seems as if the installed injectors are your problem.

 

Thanks for the response engle1147.

The injectors are the Bosch III's from Jon & FIC.
The Cold start injector was serviced there as well.

I really was not expecting any problems with the injectors themselves.
Everything worked beautifully after I installed them and the engine ran strong.
But the following day, I began having the crank/no start condition again. Later that day, it cranked and ran good again.
But then the next day, it was back to the crank/no start condition until this morning when I did the noid light test and the engine fired up.

That's what's got me so baffled.

I really hate to think about disasembling all that work again. That was a serious P.I.T.A. and if I have to pull them again, I'm not gonna be a happy camper.

That "bread loaf" looks like a bulbous eye sore that I'd like to replace with a more elegant wood grained flat panel or something more akin to
an elegant passenger glove box. (imho). Since it's not an airbag system
and I'm conscious about ensuring my passenger and I are wearing seat belts ... to me, it's just a cosmetic improvement.

But on a side note: I still want to abort that vats system if possible. I do have ways to lock down the Vette and keep it safe.

 

No doubt - taking all that apart again will suck for sure if you have to go that route.
If you've already check everything else and found no issues/problems you could check the ECM ground and/or swap the ECM out as a last resort perhaps the injector drivers are on the way out. Other than that if all you changed was the fuel injectors before the issues started and if you randomly unplug 1 of the 8 injectors one either bank one at a time before cranking the problem goes away it sure seems the issue may be injector related.

Perhaps the person/company that sold/serviced your injector(s) can help - have you asked (a form of written documentation may be in order) them for assistance/support yet?

 

Thanks again engle1147.
The old injectors I pulled out were in fact original Bosch injectors.
After watching the video on the Bosch III's, I chose to get the Bosch III's instead.
So, that's what I have mounted in there now.
I haven't yet contacted FIC Jon on this yet, since I'm leaning towards some other
possible problem as you suggest (and I suspect) might be ecm related.
I'll run a resistance check on the other injectors but I expect to find the same values
on all of them 14 +/- .5 ohms. ***(confirmed 14 +/- .5 ohms).

Pulling that ECM, (dropping it down) still involves getting access to it. But I'm given to
understand that I don't have to pull the bread box to drop the ecm. Just the same, considering what I have in mind to do, pulling the bread box is an option.

 

The computer is pretty easy to take out depending on your level of physical flexibility/ability. Drop the passenger side lower hush panel, unplug/push some of that wiring aside in the area to get access and/or to get a good look as there are 2 10 mm screws/bolts on either side of the computer that need to come out before the ECM will drop out.

 

First thing I want to do is check the grounds, but that's gonna require some athletic agility as well.
Once I make sure the grounds are clean and stable, I'll go on to the next option of
climbing in.
My flexibility is decreasing as I age, so I may have to remove the targa top so I can stick
my feet up in the air as I climb in upside down.

 

It may be easier to pull the seat so you can actually "see". Getting into an inverted position is pretty easy.....getting out of that position well that's another story.

Tip: Shut the garage door so the neighbors don't see - it helps if the car is inside the garage before you shut the door

 

Ain't that the truth.

Listen to engle. Pull the seat. Four bolts, one plug, lift out. Cheaper than a chiropractor.

 

If I had a garage, I'd do that. Closest neighbor is about 3 football fields away.
I imagine if I ever got stuck in that position, I'd probably have the surprise visit of
one of the local racoons. I can see it now.... a racoon laughing his butt off.

 

Dead short #3 shutting off the Driver (which is what is supposed to do so that you don't fry the ECM). You could check it out by moving the injector and seeing if it follows the move and then know that you need to toss that injector if it does. Heck of a lot of work, but there's no ground that I can think of - other than the ECM driver - at work here. Do check the harness closely for exposed wiring, connector terminals touching, etc.

 

The inj system is bank-fired. Basically a single fuel injector circuit thats split into two, then each into 4. The inj do NOT fire in order with the ignition....all 4 fire together. They spray closed intake valves, open valves...whatever. No pattern other than the L-R of each bank.
When one shorts so does the entire bank. Its equally as possible to short the entire system.

I've posted and written many times about the fragile and faulty C4 wire harness. I'll let you decide, but I will offer this tip, the harness trunk behind the left cyl head on the firewall that drops all the grounds to the block also has all the splices for the control circuits, grounds, INJECTION circuits, and sensors.

GM splices in wire harness are simple, protected with black tape and are prone to wire rot and separation.

You have a shorted injector circuit. Not a big deal. Hopefully its not damaged the ECM. Even if it has, ECM is only $100 these days for that model.

 

I won't be moving any injectors around since that would entail a complete disassembly of the upper deck again.
I've seen the schematics of the injector circuit and agree they are "bank fired". L-R.
The Bosch III injectors are fine as they all check at nominal resistance. 14 ohms +/- .5.
A noid light test on the #3 injector plug indicated everything was working as it should ...
and the vette started up when I ran the noid test. That got me scratching my head.

The grounds will be the first thing I check before I dig any deeper.
It isn't unusual for a ground to be at the root of this, so I'm checking that to make sure.

 

All 8 injectors fire at the same time. The light blue and light green injector bank wires are connected together inside the ECM. There is only one injector driver in the ECM.

Try removing the connector from a different injector (or two) and see how that goes.

 

This morning:
NO PULSE to the injectors.
I have not gone poking around the grounds yet.

WTF???

It was there yesterday!!

 

ON a side note:
The battery had been disconnected the day prior to the engine starting up and seeing the injectors receiving their pulses.

The next morning when the injectors weren't getting the pulses,
I had left the battery connected over night.

That tells me something reset with the battery disconnected.
But it also tells me something didn't reset when the battery was left connected and didn't start up the following morning.

Any ideas?

 

No run time,...no inj driver. BLM are also wiped clean.
It has to actually fire and run on its own to initiate inj pulses. The inj drivers are keyed off of ignition reference signals that indicate to the ECM that the engine is running on its own and not on the starter.

Its undoubtably a wiring issue. Thats why I mentions the harness in the previous post...."tip".

**************************************** ******************

"I've posted and written many times about the fragile and faulty C4 wire harness. I'll let you decide, but I will offer this tip, the harness trunk behind the left cyl head on the firewall that drops all the grounds to the block also has all the splices for the control circuits, grounds, INJECTION circuits, and sensors.

GM splices in wire harness are simple, protected with black tape and are prone to wire rot and separation.

You have a shorted injector circuit. Not a big deal. Hopefully its not damaged the ECM. Even if it has, ECM is only $100 these days for that model. "

Good luck with it.

 

Thanks leesvet.

 

Is it only the number 3 injector that is causing the problem?

What was the part number on the ECM (computer) sticker when you pulled it down/out? Some of those ECM pcb cards had recall revisions.

Next time when you have your no start/no reference pulses situation "tap" on the computer's aluminum case a few times with the backside plastic part of a screwdriver and then try to start it again.

 

I am certain that the injectors aren't the problem. They all tested at the same impedence with about 14 ohms.
When they were getting a signal, they worked fantastic. The next day, they weren't getting any signal at all.
From what I've been observing so far, it seems the ecm is either the culprit or just
not responding from the real culprit that might not be sending a signal.
The only code I get is 46 (vats). But if the injectors aren't shooting because they're not getting their pulse from the ecm consistently, it's telling me that the ecm isn't getting
the signal it needs and/or that the signal is failing to be sent by the ecm.
So that's either the ecm itself, or vats or even a reference pulse from the distributor.
Could even be a combination of either or all three.
Every day that I've gone out the check the situation, this time it has failed to run at all. Even after disconnecting the battery over night.
I checked the injector plugs, and sure as heck, they're not getting a signal.
The engine tries to light up, but that's only because it's feeding off the cold start injector which is insufficient to run the engine for no more than a few seconds.
So, it's not "crossing over" to the regular injector feed circuit from the ecm.
The first thing it makes me think of is the ecm itself and the injector driver contained within it.

I haven't been able to open the dash enough to get a look at the ecm. I'm having
a difficult time getting the bottom panel to come off.
As soon as I do get that panel off, I'll drop the ecm down and take a look.
When I find out what number it is, I'll post it here.