Engine sometimes acting strange. I'm all out ideas.

[Camatruder]

Hi guys, I have an occasional hesitation and sometimes it even stalls. I also notice that I have a lot of white-gray-ish smoke when cold and a little of it when warm and at idle. The smoke does not smell sweet, it smells like ordinary exhaust smoke. When I’m parked and at idle and give it gas a couple of times there’s a puddle of water behind both exhaust. These exhausts are dual not connected lines and the smoke and water are the same at both. I’m not sure if the smoke and water have always been there and/or it is related. It’s not very cold at the moment here, about 9°C (48°F).

I don’t have any codes (except for 12 ofcourse).
Compression is good and the same at all cilinders. I tried a pressure test at the cooling system and I think it holds pressure (I had some problem with a home made pressure tester that I made in a hurry).

I have spark at all cinders also when acting strange during surging (I hope I translated this right, I mean that the rpm changed rapidly between 500 en 900 rpm at idle). I changed the plugs to be safe but it did not help. I don’t know how to check the quality of the spark.
Timing is correct (0° with the tan wire disconnected, 8° BTDC when it is connected). I could not check timing when acting strange as I could not trigger these events when I tested.

Vacuum is good and steady at 21Hg and is hold for hours after that engine has been shut off.

EGR valv seems to be in good working order.

My truck runs both on petrol or on LPG (propane) and this occurs on both fuels so it is not fuel related. In fact when it starts acting strange on LPG , the engine almost always stalls completely. I think this is because LPG needs a better spark than petrol.

I’m thinking icm or high tension coil or may be intake manifold gasket. Or maybe an out of control choke (i don't know how the choke is controlled in a tbi). I hate just throwing parts at it because these shipping and customs costs are too much).

This is my daily driver and need to solve this quickly (or just keep driving till I something gives).
Any input is highly appreciated.

 

[Honky Kong jr]

Could have an ignition module failing. As far as the smoke it could just be steam due to conensation which you have if you have water coming out of the exhaust.

 

[Snoots]

Almost sounds like a fuel starvation issue IMHO. I wouldn't worry about the steam or water out of the exhaust. You will definitely notice a positive difference if you put a balance tube on the exhaust tho.

 

[1987 GMC Jimmy]

I'm thinking your vacuum would be much lower if it was an intake manifold issue, and you'd be having a different set of issues if it was the ignition module like losing/altogether not having injector pulse and/or spark. I think you might be on the right track with the choke postulate, but the TBI equivalent is an idle air control valve (IACV). That's what I'd be looking at. If the condition improves, as you add throttle, I'd look at that. The first thing you should do is the relearn procedure. What you do is jump your A and B pins on the ALDL, turn your key on but don't start it, wait thirty seconds, unplug the connector for the valve (four wire connector on the passenger side of the TBI unit), turn the key off, undo the jumper, and reconnect the valve. If that doesn't provide a long term solution, I'd consider replacing the valve with strictly the AC Delco part.

 

[Camatruder]

Prior to the problems I had my battery removed for a couple of days to repaint my rusted battery tray. Maybe this relearning of the IACV that Jesse mentioned was what happened. Anyway i took it for 3 (short) rides without any issues.
It still smokes even when warm but that may have always been the case. The LPG was already installed when i bought it and i know many installers put in a cooler thermostat because LPG tends to create more heat. My gauge always shows the needle at the mark between 100 and 210°F. I measured the engine with an infrared thermometer and got 180°F when warmed up completely. Could that explain the smoke ?

Anyway, tuesday i have a lot of miles to cover including some highway. We'll see what happens.
Thanks!

 

[1987 GMC Jimmy]

I think you misunderstood me there. The IACV relearn is a procedure that you perform to reset the valve. It is not an adverse effect of resetting the computer. It will sometimes fix idle quality issues because the computer cannot reset the valve itself; it only knows what position the valve mechanism is supposed to be at a given time. I don't think the white smoke after startup is abnormal, but it is a little strange that it persists until after it's warm. Mine does the same thing when it's cold, though. I know that LPG combustion results in higher temperatures, but the petrol side of your engine wants to operate at 195*F. It's kind of a catch 22 there. Run a cooler thermostat but inhibit your engine's performance and efficiency, or run the correct one and put more stress on engine components when it's running LPG.

 

[Camatruder]

Hi jesse, i tought the relearning procedure happened automatically every time the battery was disconnected long enough. Thanks for re-explaining. Next time i order parts, i"ll include and place a 195°F thermostat and see what happens. Now i don't see any change in coolant temperature when i'm on LPG or petrol.

 

[1987 GMC Jimmy]

No, the relearn procedure is as follows. The A and B pins on the ALDL connector are the top two right hand pins facing the connector. Hopefully all that translates correctly, but if not, feel free to have me clarify.

What you do is jump your A and B pins on the ALDL, turn your key on but don't start it, wait thirty seconds, unplug the connector for the valve (four wire connector on the passenger side of the TBI unit), turn the key off, undo the jumper, and reconnect the valve.

 

[Camatruder]

Thanks! I did understand. If the issues should re-occur, i'll definitely give it a try.

 

[Camatruder]

Just got back from a 100 miles trip and no issues whatsoever. Don't know what went wrong there for a couple of days.