I'm stumped and could use some advise. I'm working on a friends 1995 jimmy, the car stalled and he had it towed to my house. I went to look at it and it started and ran fine. This truck has the obd 1.5, I borrowed a tech 2 and pulled the following codes p0141 p0300 p1406. I know egr and fuel lines are issues so I pulled the plenum and egr valve. egr valve looks fine no carbon on the valve or the ports, I put it back with the screen gasket. moving on the plenum, the injector was leaking fuel from the regulator and the housing so I replaced it with a new BWD injector, I also did the "nut kit" while it was apart. put it back together and it runs fine, I took it on a test drive and it is horrible. The truck looses all power but doesn't stall. I hooked up a fuel pressure gauge and I have between 53-60 psi depending on load, the truck maintains good fuel pressure during power loss. I monitored the o2 sensors b1 s1 fluctuated up and down as it should, bank 1 s2 (post cat ) doesn't switch at all, I'm not a GM tech but every car I've worked on the fuel trim isn't affected by post cat o2 sensor, I figure it is bad but I know it isn't causing my issues, I replace it same issues. I'm now monitoring everything with a snap on mt 2500, not as detailed at the tech 2 but should give me the basics. I go on a test drive with a buddy who is a gm guy, we monitor everything and nothing seems to be bad. o2 sensors are working fine, no misfires detected just a loss of power. The truck was due for a tune up so it got new Delco plugs wires cap rotor still no changes but the parts were needed. my GM friend said he has had his *** kicked by a coolant temp sensor and a coil before on the same truck, even though they tested fine he replaced them and all was good. I hate to throw parts at a car but they were cheap and I've got nothing else to go on. replaced the sensor and coil... guess what same **** but I have a few twists. first twist is once in a while the scanner looses communication with the truck and asks me to reenter the vehicle information. the snap on scanner uses a 9 volt battery for memory and what not I just figured this was bad so I replaced it, same **** looses communication with PCM but the scanner never shuts off so I know I have good power and ground to the scanner, I tested the pin for the communication line in the DLC and it feels good. so the PCM might actually be loosing communication. the scanner works flawlessly on other cars...... twist number 2 I was on the post coolant sensor/coil test drive, truck has no power (not like alternator I mean it doesn't make any power) and the transmission starts to slip, will not go forward in OD or D, I put it into 2nd and it starts moving, I pull into a side street to turn around and go home. reverse works fine, I put it back into OD and it goes forward with no issues other than the above mentioned no power.... when the truck went into transmission slipping mode, the abs light came on. I pulled the codes and had implausible signal codes from all 4 wheel speed sensor, and I had a high and low voltage code. I cleared the codes and they never reset..... now you know the symptoms. I've never had my butt kicked by a car this bad. I've read that ignition control modules can cause similar symptoms but I think they are usually good or bad not much grey area with solid state electronics... my other 2 thoughts are bad ground somewhere or maybe even a bad PCM. can anyone think of anything else I should try or test. This truck has the distributor with the wires on the side. also one thing I noticed is the scanner doesn't read the crankshaft position sensor, it doesn't give you the option.


Couple of things i forgot to add. i did check for vacuum leaks, i did put a vacuum gauge on it to check for plugged exhaust.

 

I would personally start by checking all the grounds battery and body first to ensure they are tight and clean for good contact. does the engine tempurature rising or change at all when you lose power or when transmission did its little twist. also i am pretty certain if your crank sensor was bad you would have random misfire codes or a reall horrible running engine but i would focus on grounding points first plus give the battery a good load test.

 

does anyone have list of ground locations? i've checked the one at the rear of the engine, the main ground cable at the battery and the body/block, i don't get any voltage drops at any of the grounds i've tested. i was hoping GM hid a ground somewhere that i'm missing. The temp doesn't change when the car acts up. when the car is just sitting i can rev the engine with no issues and it idles great, the failures happen when it is under load and warm. it will fail when in closed or open loop. i didn't think it was the crank sensor i just found it odd that the snap-on scanner will not read it. i can't remember if the tech-2 was able to read it or not. has anyone had an ignition module fail only when hot and under load?

 

Mine would loose power and the trans messed up and it was all due to my ignition modular check it out.