Hello everyone,
been working on my son's '88 Dak (3.9, manual) and can't find the problem, now i'm lost...

Symptoms: at WOT acceleration truck suddenly lost power, but did not stall, it keeps running well, with less power. Two days after, it start stalling at idle, and, if you stepped on gas, die or rev. So now truck start fine for 1 or 2 secs, then you have to play with gas pedal to keep it alive. The motor doesn't seems to be ''shaky'' when running, it turns smooth but just wan't to stall. Smell to run really rich, i'd say: eye burning rich...

Been done: code sequence (12, 24, 33, 55), so 12 and 55 known to be start and end, 33 is A/C related (no A/C on the truck), 24 is the code left, related to correlation between MAP and TPS voltage or TPS low or high voltage. MAP tested OK but TPS tested wackly, put a new TPS. Still the same condition.
Tried a known to be good MAP, still the same, put back the old MAP.
Tried a known to be good O2 sensor, still the same, put back the old one.
Cleaned TB, checked vacuum hoses, unplug battery (code 24 disapear).
Plugs and wire are almost new, rotor and cap are new.

Did a lot of searches on forums and internet, just can't put my finger on it...

A little help would be apreciate !

 

The MAP code could be bad wiring and that could be your problem. Did the TPS code come back after replacing the TPS and after a reset of the codes?

It could be a bad vacuum leak to incorrect fuel pressure.

 

Code was 24, my understand is that it could be MAP or TPS or both. Code didn't show up after TPS replacing.
Trouble still the same when trying a new MAP. (i put the old one in place)
I will recheck vacuum hoses, first inspection didn't show any leak.
I will find a way to check fuel pressure.
Could it be related to EGR valve ?
could a bad O2 sensor cause that and, if so, a new sensor would resolve the symptom instantly or after a couple of minutes of running time ?

 

I was able to run it a while after putting a gas line bottle (maybe there's water in the gas ). Once at temperature, after about 10 minute running with me going crazy on the gas pedal, it started to maintain rpm at around 3000 then i've been able to lower a stable rpm to about 1700. Still stalling if i take my foot of the pedal.
I guess fuel pressure should be good, as i've been able to run 3000 rpm for as long as i wanted to.
After that i took of all 6 plugs, there're all OK. Nice white light deposit, no dark deposit or wet plug. But, altought there were supposed to be OK, 4 of 6 wire looked burnt. connectors falling of the cable.
Now waiting for a new set of cables.
we'll see.

 

New wires installed, IAC cleaned et lube (was not really dirty).
Can run the motor idle if IAC is plugged in but not bolt in place, it turns about 500 rpm and running rough.
So bolt back IAC in place and adjust IAC plunger 3 turn shorter.
Now motor is running more stable, if i press lightly on gas pedal, it idles at about 1100 rpm but hunting +/- 100 rpm (from 1000 to 1200). Running smoother but not perfect. If i do not touch the pedal, it hunt for idle and dies.
Before banging my head, i checked resistance on coil, low voltage side gives me 5.3 ohms, infos that i found said it should not be over 1.6 ohms...
Is that right ? Could it be the coil ?

 

New coil, new pick up coil, found some corrosion under the pick up coil, cleaned.

Problem still there. Wont stay at idle, when it does, for a few second, it hunt from 600 rpm to 1000 rpm a couple of time then dies.

 

not sure if it helps but i had a problem with my truck either not idling or have an extremely high idle. after a few months of tweaking and testing i found my iac (forgot the actual name for it) would either push out completely or not work at all even after cleaning it. so i unplugged it and turned the screw till it idled around 500rpms +/-. the only problem i have now is when i get off the highway it fells like it dies out but it just returns to idle.