Chevy & GMC Vans

Good morning all,

I was working on a problem in another forum and Smalley recommended I come here. Here is the story:

I hope you can help.

The vehicle is a 91 chevy astro 4.3L with 100k+ miles
About 2 or 3 weeks ago, very occasionally at first, the engine would suddenly die. There was no warning , no sputtering, no hesitation, it would usually just die. But it would start right back up and run fine afterwards.

As time progressed, the problem became more frequent, and sometimes you’d have to grind a bit to get it restarted.
Yesterday it died on my wife and is now very hard to start and will only run a few minutes if you’re lucky.

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.

I started by replacing the fuel-pump relay, which seemed improbable but was easy and cheap.

Next I replaced the fuel filter.

Then finally I installed a fuel pressure regulator diaphragm kit. I really thought that would be the one that
would do it – but no soap.

We had the fuel pump replaced about 2 years ago – supposedly with an oem (they certainly charged us for an oem) so I haven’t been looking in that direction.

But just in case I decided to check it. I didn't have the adaptor to go inline so I had to check it head-in. It came it at right at 13psi - so that part looks good.


I hooked up an analog volt meter to one of the injectors hoping to see if the signal to the injector was dropping out.

I expected to see a pulsating voltage across the two injector leads but instead I saw almost no voltage - even when it was running "properly".

So I measured each lead to ground - both running and not.
In both cases I saw 12 V when running. As/after it dies (cant tell which) it drops to about 11.5 then drifts up to 12.5.


I tried putting a timing light on a plug wire and on the coil wire to see if the ignition module was firing when it wasn't running. With an inductive timing light on the coil wire, I cranked it and it had trouble starting but the coil was definitely firing. It's possible that it was firing weakly and/or missing part of the time as after it started, the light was more continuous and brighter.


I took the igintion module out and took it in to Advanced Auto and had them test it. They tested it 6 times and it came up good every time.

I jumped on JustAsk to get an idea where to go next. The justask guy 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...

The problem is pretty intermittant. Sometimes you can barely get it started and barely keep it running, other times - like when you're trying to check something - you can hardly get it to die and when it does it starts right back up. It can happen when the engine is stone cold, or running warm - although I've had a little better success at getting it to be hard-starting when it is cold.

Any help you can give will be greatly appreciated. I am not finished with the justask guy so he might have an idea as well. I'll post the solution once I find it



PS

A side note on the fuel pressure regulator diaphragm kit. When I was installing it I saw something that looked strange to me. I have never had that area apart before so I don’t really know what normal looks like but let me try to describe what looked odd.

Picture the assembly that the spring and diaphragm fit in. Now flip the whole assembly over. At the bottom of the bowl there is what looks like a port – about half an inch in diamteter, that fits down into a hole in the throttle body.

What I saw was, looking into that port, it looked like a large glob of molten copper (or copper colored metal) was plugging the port from the inside of the bowl. It didn’t look machined, it had about the same appearance of if you took a large glob of molten solder and dropped it into water – roundish and rough.

Since there is a slot in the side of the bottom part of that bowl that a tab comes through – I think to lock the pressure adjust screw in place – it doesn’t seem like any gas would be going into that part of the bowl. So it doesn’t seem like the glob would matter. But I thought I’d mention it.

Thanks for your help!

Glad you made the trip over here from AF.com!

Someone here will be able to help more than I have so far I hope. ;)

Hi Smalley,

Glad to be here.

The justask guy is giving an answer that it sounds to him like the injectors are leaking fuel out of the line or the fuel pump is allowing fuel to flow back into the tank. This sounds improbable to me because if that were the case I would think it would be hard starting (if you didn't simply charge the system once or twice before starting) but would not make it die while running as the pump would keep it pressurized.

What do you think?

k

I'm leaning toward a faulty fuel pump. Or maybe the electrical connection at the pump is bad. Put a fuel pressure gauge on it and watch it while you drive.

My '97 had the same thing happen when we got it used. It would just die, but would start up right away. Eventually it stopped re-starting, and it was the fuel pump, so my leaning it toward that as well. Having a pressure tester on it while driving will show what is going on pressure wise.

Doing that kind of driving test with a TBI is going to be hard. I doubt that his pump is weak given he sees 13psi, which is the upper limit of TBI pressure. Oh wait a minute. I just had a thought.... what's that thing inside the tank, between the pump and..... the pulsator?

Also I just dug out my FSM for my b-body, can't find the Astro FSM. You said your pressure was 13psi. Was it OVER 13psi? The charts I am reading indicate you need to replace the fuel pressure regulator if the pressure is over 13psi.... Or there is a restriction in your return line to the tank.

It'll defintely be hard to do the driving test - no shrader and no in-line adaptor for that vehicle.

The pressure read right at 13psi - at least on my cheap gauge.

I did install a new regulator diaphram kit, unless you mean the whole metering assembly.

I don't believe this model has a pulsator - I checked the advance-auto website and searched for pulsator for that model and it as greyed out - which usually means it's NA.

a blockage in the return path is a possibility - how can I check that?

Thanks,
k

Unhooking the return line, from the rear of the TBI unit the right line, and blowing through it should tell you. I kind of doubt that is it though.

If is was 13psi and not some huge number you should be fine. I have a modified TBI with a vacuum modulated fuel pressure regulator on my 89 9C1 that I run at 17-27psi depending on vacuum. Anyway....

Might be time to check your connections at your ECM. Make sure they are good.

I took it out for a test drive because it seemed like it was running pretty well the last couple of days. I drove it for about 15 mins at speeds up to 57 (the fastest I could get the traffic to move) and every thing was running fine (although maybe a little warm).Then after a little in-town driving, I pulled up to a stop light and it died. I got it restarted - a little more cranking than usual was required and the battery was fairly tired - and resumed driving. A minute or two later while driving at about 30, it died again. I got it restarted and got it home.

I don't think this has any new clues in it but maybe it'll spark a thought.

Also, is the return line the line on the left side of the TB or right (as you're sitting in the passenger compartment). I think it's right?

Thx

I've never had this happen to my 95 but I used to have an old delta 87 and it would die suddenly and without warning. I ended up changing the coil pack out and it worked fine after that, can't guarantee thats your problem here but hey you never know, and the coil is a fairly cheap thing to replace. Good luck and let us know how it turns out.

I would be leaning toward a faulty ignition control module/pick-up coil. Sounds like it is quitting intermittantly when it heats up. I know you had it tested but it sound like it is an intermittant fault which will probably not show up on a simple test done at a parts supply store.
Here is a simple confirmation test you can do on the intergity of the rest of the system to eliminate them as being faulty.
When the vehicle dies & will not restart - confirm you have no fuel spray....
If you have no fuel spray from the injector, unplug the 4 wire connector from the distributor ignition module. Take a simple test light & connect the wire clip to a power source. Tap the tip of the test light to the terminal in the connector on the harness that goes to the purple/white wire.
This will create a rpm signal pulse to the computer.
What should happen is
1: the fuel pump will turn on,
2: the injectors will pulse & spray fuel,
3: the coil will fire.
If this happens, the ignition module & pick-up coil should be replaced.
If this does not happen, further diagnosis will be required.

I hope this helps you to resolve this issue & best of all it costs you nothing to check - no special tools, no parts to buy/try.

Note: I say both pieces should be replaced because it is a good practice to replace both together. I have diagnosed one piece or the other & replace just one, only to have it return a week later for the other.

Thanks for the input guys.

I have pretty much (I think) narrowed it down to fuel problem by doing the following:

wait until it is hard-starting, visully check there is no gas coming out of the injectors, spray carb cleaner int the throttle body and the engine fires: ergo spark but no fuel.

I did a volume test - since I want to siphon a bunch of gas out anyway - and in 10 secs of charge cycle (key on 2 secs - wait 10 - repeat ) for a total of 5 times, I got 22 oz of gas. My book says at least 1 pint in 15 secs - so that looks ok too (ps that was post-filter)

thanks for your help - all input is appreciated!!

I haven't heard bak from the JustAsk guy - I think he gave up.

OK here is the latest.

I drained all of the gas - to the point the pump couldn't pump any more, poured about a gallon back in, drove it over to the gas station, and put 5 gals of premium in, and it died while setting at the stop light after leaving the gas station.

Maybe I didn't go far enough to clear the lines but it doesnt make me hopeful that it was bad gas. (plus that wouldn't make the injectors not fire unless they clogged - in which case they'd stay clogged).

Right now it is not being hard-enough starting to try V8famvan's test but if I get a good no-start period I will give it a try.

Unfortunately if I don't get it today, it's going to have to go to the shop Monday - school starts next week and we'll really need it.

PS. I did try wiggling the wires at the ecm while it was running but no luck. Hardly conclusive but better than a poke in the eye.

We'll possible good news. I hate to risk posting before my chickens are hatched but there is a promising development.

The justask guy had me jumper the switch pins on the oil pressure connector. It ran for a good 15 mins without dying so I hit the parts store just before they closed and got an oil sensor and put that in.

I started it up but a few minutes later it died and I was quite discouraged. I restarted just in case and this time it ran 15 mins in the drive and I took it on at least a 15 minute test drive with no problems.

I'll drive it tomorrow to church and to work Monday and see how it goes. If things are still looking good then I'll repost and let everyone know...

Which one did you replace? It's my understanding there are two on these engines. One that give a reading to the gauge on the dash and one that goes to the ECM.

Is that right guys or am I off?