Chevy & GMC Vans

I can't say for the Z engines, but the W series has only one Cecil.

Give v8famvan's diagnostic a try wolf8963.

They're combined into a single unit with 3 pins - 1 for gauge, 2 for switch.

but Bad news,

Tried to start it Sunday, cranked until battery was dead. Put jumper pack on it and finally got it started - died twice in driveway. Started down road and it tried to die twice So I turned around and went back home.

Problem definitely seems worse first think in morning and when its completely cold - though it does it any time. Still no SES codes.

Would have been a good time to try 8famvan's steps but I was on my way to drive a bus and I won't work on it on Sunday (gotta have 1 day off from the frustration!!!).

To top it all off, my battery charger is dying - only putting out 11.5V - which charges a little but cant keep the battery up to full charge.

It never rains when you snore... or something like that...
quite frustrated!

Another thing that I thought odd at the time. When I was jumping the pins on the connector for the oil-sensor switch, 2 things:

First the pump came on right away (even with key off) and stayed on.

Second, I used a jumper wire that was either 22ga or 20 ga and it was carrying enough current to make the wire slightly warm.

Then later the wire was nice and cool...

Does that sound right?

And has anyone put a pressure regulator diaphram kit in one of these? Did that PS I included on the first page sound like a problem?

This is probably not what you want to hear, but until you do a fuel pressure test you are just poking around in the dark.

I did one. 13psi. Also did a volume check - 22oz in 10 sec.

thx

Perhaps you don't have any sparkage going to the plugs. Have you checked your ignition coil?

my first thought is along the Captain's line, the ignition coil.
one other suggestion is to check the spray pattern on the injectors. Both my original injectors gave up the ghost at the same time, pee'd gas into the intake, flooded the engine. It died on me while cruising at 60 mph. I pulled over and managed to get it restarted. The poppets in the injectors were intermittantly sticking open. It wasn't long before the stuck for good. Odd thing was I wasn't smelling a lot of gas like you would expect.

OK folks,

We may have a resolution...sigh....

We took it in to shop today - wouldn't you know it, it ran fine the whole way.

They had trouble getting it to act up enough to track it but ultimately the found they could get a fairly repeatable issue by letting it get warmed up and then shut it down, and when they restarted it would frequently be hard-starting.

at that point they said they were able to see that they were loding the "noid" bump or signal that causes the injectors to fire. They wound up replacing the ignition module.

That kills me. I had it out and at the parts store and nearly decided to replace it twice. Instead I paid someone $200 for the priviledge!

Of course until we've driven it a couple of days, we won't be comfortable. But it seems to be running properly for the moment.

Thanks for all your help!!!! I hope the information here (assuming it's fixed) can help some other poor guy in misery.

If anyone is so inclined, you might post an explanation of the whole "noid" signal thing. I have an o-scope. If I know what I'm looking for, maybe next time I can find it.

Thanks again
$200 bucks lighter

James nailed it on the previous page...and I'd be willing to bet he can provide the entire tech background on it.

BTW,

I noticed after I drained my tank (disconnected line from fuel filter and let pump run it dry until pumping air) that my gauge still read 3/16ths of a tank.

Is there any easy way to calibrate this?

thx
me

So it WAS a sparkage problem. Next time, give it a shot of starting fluid. If it starts, it's a fuel delivery problem. If it doesn't start, look at the electrics.

Glad to hear that this seems to be resolved for you, albeit $200 lighter. You would have determined this if you used the test method I mentioned, had it acted up for you at a reasonable time for you. Ahh, electrical intermittants... the bane of my job. Oh well, keeps me employed.

As I posted previously, it was the ignition module. Not to say i told you so, because I did not know & cannot know - for sure, unless you say so. I did however have a very good feeling that it was the ignition module based on the information presented in the original posting in this thread.
The right 'clues' were in there:
1) Make/Model/year/engine. The vehicle is a 91 chevy astro 4.3L
2) Good description of the condition/symptoms. Last night I pulled off the air cleaner and junk so I could see the throttle-body injectors. When it’s running they appear to be firing fine, then suddenly they’ll just stop firing and the engine, of course, dies
3) List of facts or what is known to be good. replacing the fuel-pump relay, replaced the fuel filter, installed a fuel pressure regulator diaphragm kit, fuel pump replaced about 2 years ago - It came it at right at 13psi, the coil was definitely firing,
4) Some actual diagnostic information. had me spray carb cleaner down the throttle body while it was not starting. I should have thought of that. In any case it fired so the problem is still on the fuel side...


I have underlined what is a BIG clue as to the direction of the fault. Engines need 3 things to run, AIR - FUEL - SPARK. If you suspect one of the 3 is an issue & you substitue it & it runs - you are on the right track. This defines it as a FUEL supply issue. The fact that the engine shuts off suddenly, is also a clue. If it was a fuel pump pressure issue, the pressure would die off gradually, causing a stumble stall/sag/hesitation/lack of power - take your pick.

How to understand this. The fuel pump is turned on by the ECM on initial 'key on' for fuel pump priming. Once the ECM recieves an ignition reference signal from the ignition module (cranking or running) it turns on the fuel pump, via the fuel pump relay. The computer also uses this ignition reference signal to trigger the fuel injectors to allow fuel spray. This fuel spray, stopping suddenly, matches the symptoms/parameters mentioned in the post. Essentially the reference signal to the ECM is dropping out causing the injectors to stop firing. Obviously the base signal to fire the ignition coil was still working as the engine would fire up if carb cleaner was sprayed down the throttle body. Just a process of elimination.

Side note: The oil pressure switch is used as a back up should the fuel pump relay fail. (A faulty fuel pump relay will cause an extended crank condition, as the pump will only turn on after the oil pressure has built up to the point where it closes the contacts.)

wolf8963 wrote:If anyone is so inclined, you might post an explanation of the whole "noid" signal thing. I have an o-scope. If I know what I'm looking for, maybe next time I can find it.

A noid light is basically a specially adapted test light that just easily plugs in the injector connector so you can visually see what is occurring electrically - the on/off is occurring.

wolf8963 wrote:I noticed after I drained my tank (disconnected line from fuel filter and let pump run it dry until pumping air) that my gauge still read 3/16ths of a tank.

Is there any easy way to calibrate this?

Easy is relative.....You will likely have to take out your fuel level sender from inside the fuel tank to rectify. Either you have something in the bottom of the tank inhibiting your sender float from finishing a full swing or you have an electrical issue.

CaptSquid wrote:So it WAS a sparkage problem. Next time, give it a shot of starting fluid. If it starts, it's a fuel delivery problem. If it doesn't start, look at the electrics.

Actually I did that and it fired - my understanding is - and someone who knows please correct me - that the signal that fires the injectors either comes from or through the ignition module. So I had spark, but for whatever reason it wasn't always firing the injectors

thx for your suggestion though - hopefully I'll remember it.

James,

yep. You are definitely on my A-list for next time around (which I hope never comes)!

How to understand this. The fuel pump is turned on by the ECM on initial 'key on' for fuel pump priming. Once the ECM recieves an ignition reference signal from the ignition module (cranking or running) it turns on the fuel pump, via the fuel pump relay. The computer also uses this ignition reference signal to trigger the fuel injectors to allow fuel spray. This fuel spray, stopping suddenly, matches the symptoms/parameters mentioned in the post. Essentially the reference signal to the ECM is dropping out causing the injectors to stop firing. Obviously the base signal to fire the ignition coil was still working as the engine would fire up if carb cleaner was sprayed down the throttle body. Just a process of elimination.

Yeah, what kind of threw me off here (besides not knowing in nearly as much detail as you have presented here!) was that I put an analog meter on the injectors looking for something to seem to drop out when it died and it didn't -even after it died. Since I didn't see a change I was reluctant to think the injectors were losing signal - stupid because obviously if what I was seeing by the meter would have been pertinent, the injectors still would have been spraying fuel even after the engine died!!! Possibly if I would have put the o-scope on it instead of meter I might have seen the change. What should the signal look like on the injector?

Side note: The oil pressure switch is used as a back up should the fuel pump relay fail. (A faulty fuel pump relay will cause an extended crank condition, as the pump will only turn on after the oil pressure has built up to the point where it closes the contacts.)

That was something I'd seen on another forum but all I could remember was that it was supposed to be a dual-path system and I couldn't remember for sure what the other path was - and by this point I was thinking a double failure after it ran so nice when I jumped those contacts.

To be honest it took me a while to get back in the auto troubleshooting frame of mind. My brain just didn't want to go there! But alas, my wallet demands it!

Thanks for all of your help and everyones!