Chevy Astro and GMC Safari Forum banner
1 - 20 of 28 Posts

·
Registered
1986 base model Astro 4.3
Joined
·
12 Posts
Discussion Starter · #1 ·
Greetings Fellow Members,

I'll try to be brief; I need help. I'm no mechanic but have some skills. 1986 Astro 4.3, 150,000 miles original problem. stall after a few minutes driving, would restart and idle enough to limp home, any push of the accelerator would cause severe stumble and or stall again. Then it was stolen but recovered, sat for seven years. Now is a "retirement project". I thought it was a fuel issue, replaced the following: Delphi fuel pump, rebuilt TBI, new injectors, plenty of fuel pressure and volume, return line unobstructed. Wires cap rotor plugs all good, new module. Timing TDC and steady. Afterwards, (bypass reconnected) timing light showed 8-10 advanced at idle but the second you put your foot in it, retard 20 degrees opposite direction, stumble and near death. So..., replaced knock sensor (genuine GM), E.S.C module, ECM. Checked routing of all wiring, ESC module has power, grounded and sending 9 volts to ECM but the ECM still insists on retarding the spark 20 degrees. This is driving me a little crazy all over the course of the last 15 months or so. I don't own a scan tool geez, might need one. Am I missing something? Any thoughts would be greatly appreciated.
 

·
Registered
Joined
·
612 Posts
Did you check for codes? That will at least give you an idea of what's going on.

Here's the diagnostic tree from my FSM. Mine is a 94 but the info is still the same.

Font Material property Parallel Schematic Paper


Font Publication Material property Book Handwriting


Font Material property Parallel Schematic Engineering


Font Material property Handwriting Parallel Pattern


That should give you a place to start.
 

·
Registered
1986 base model Astro 4.3
Joined
·
12 Posts
Discussion Starter · #3 ·
Thanks Bikley, appreciate your effort. I have had codes but only related to unplugging sensors in the diagnostic process the latest being '"43", ESC.. the older codes (1986) are somewhat crude. I have two books on this model but have never seen flow charts quite like the ones you posted thanks, I'll give them a shot.
 

·
Registered
Joined
·
612 Posts
The first thing I'd do is clear the codes, then make it do what it's doing and see what codes, if any, get stored. Always make sure the battery is fully charged and the alternator is working properly. A bad battery or alternator can make all kinds of things go wonky.

A couple other things that can affect timing are the coolant temp sensor and the MAP sensor so you might take a look at those too.
 

·
Registered
Joined
·
612 Posts
but have never seen flow charts quite like the ones you posted thanks, I'll give them a shot.
Disregard those. I realized that your ignition system is different.

Try disconnecting the knock sensor and see if it still retards the timing. If it runs more like it should, we have to figure out what's causing the knock.
 

·
Registered
Joined
·
226 Posts
Those charts are from the factory service manual. There are three in the set, I think. Service manual, fuel and emissions diagnostics, and electrical. You need all three specifically for your year (fuel and emissions covers all the light trucks, too) and your life will be magnitudes easier. Soooo much better than Haynes or Chilton.
 

·
Registered
1986 base model Astro 4.3
Joined
·
12 Posts
Discussion Starter · #8 ·
Thank you Bikley and opelbits, I just ordered the manual. Just fyi, here's a list of the rest of the parts chasing I've done; coolant temp sensor, TPS, MAP, O2, EGR, cleaned and refitted IAC. (This is embarrassing.) Ran separate wire to eliminate any possible interference; knock sensor to ESC, ESC to PCM terminal B7. ESC is getting 12 volts and ground is good. Battery is good and charging system great especially after finding and cleaning ALL grounds. Thank heavens for beer or I would have thrown in the towel already!
 

·
Administrator
Common Sense + Critical Thinking
Joined
·
14,261 Posts
This is a steal. $7.20 + tax
That is an awesome price for a factory manual, which are worth their weight in... well maybe not gold, but they are well worth it ;)
 

·
Administrator
Common Sense + Critical Thinking
Joined
·
14,261 Posts
I have been scratching my head on this one, any difference with the knock sensor unplugged?
 

·
Registered
Joined
·
612 Posts
I have been scratching my head on this one, any difference with the knock sensor unplugged?
That's what I've been waiting for.

A knock is about the only thing that I can come up with that would cause the ESC to retard the timing that much. Red has said that it sat for a long time so it could be carbon deposits causing detonation. Another thing it could be is a vacuum leak in the intermediate or WOT range. The mixture becomes so lean that it has to pull the timing way back just to get combustion.
 

·
Registered
1986 base model Astro 4.3
Joined
·
12 Posts
Discussion Starter · #13 ·
OK, ran it with knock sensor disconnected, might have tolerated revving a bit more but still falling on its face and can't sustain anything above idle which by the way is rich. Plugs were wet and black historically, changed to plugs one step hotter. No new codes but now that you mention it, had a code 44 (lean exhaust) months ago, just one, never saw it again. Replaced all vacuum lines during the TBI rebuild, used propane to check for leaks everywhere including intake gasket which I've read can be a problem with these motors, no leaks found. Both injectors spraying evenly, nice conical shape. It is hard for me to tell if the duration of the pulse is longer or if adequate fuel is being provided Not being able to maintain a higher rpm is getting in the way of diagnosis otherwise, I would run it at 2000rpm, kill it and check the plugs. Runs smooth and quiet at idle all day, I think I can rule out engine noise. Hope I'm not muddying the waters, I should have kept a journal with all the bloody stuff I've tried over the months. Is it possible to check for a leak at intermediate or WOT?
 

·
Registered
Joined
·
612 Posts
The more I dig into it the more I'm convinced that it's an ESC problem. It's wonky and everybody hates it. 😃

There's 2 common solutions.
1. Bypass it. You can unplug the 4 pin connector and snip and splice the black and green wires, or, you can buy a little adapter that plugs in to the connector and does the same thing.


The downside of that is you won't have any retard or advance so it probably won't run great but it will run.

Solution 2.
Stick an hei distributor with vacuum advance in it.

 

·
Registered
Joined
·
612 Posts
Ok, I'm into the not sure area again. On the HEI distributor I think the tach signal would have to be sent somehow to the ECM so it knows when to fire the injectors. Hold that thought. I'll be back. 😃
 

·
Registered
1986 base model Astro 4.3
Joined
·
12 Posts
Discussion Starter · #16 ·
Hi Bikley,
I'm "retired" but still have five kids at home, spare time can be hard to find so forgive me for not commenting sooner. Thanks for your suggestions, The EST bypass won't work with my set up unfortunately. (enclosed image)
Font Parallel Schematic Pattern Art


I don't know if you can use the vacuum advanced HEI without going to a carburetor which would most likely mean a new intake manifold also. I do have a separate unused tach lead which I have taped off. Is there any provision for using that HEI with a TBI? As far as bypassing the current set up if it is even possible, I lack the knowledge and confidence to try for fear of screwing up the ECM. In the meantime, I'm going to double check the operation of the current ignition module and also, the pickup coil tests good resistance wise but I haven't tested while it's hot. Other than that, I feel like I'm at an impasse.
 

·
Administrator
Common Sense + Critical Thinking
Joined
·
14,261 Posts
You said the ESC is giving 9v, which would mean no knock, but is the wiring and connections good from there to the ECM or is the ECM seeing 0v?
 
1 - 20 of 28 Posts
Top