Chevy & GMC Vans

we noticed that as you held the key to start position it would fire & run , once you let go of the key it would die . so we're replacing the ignition switch on the lower part of the colum to see if that helps . tryin anything at this point !!!!

Have you popped the doghouse at night and looked for any sparkage? does this van have A.C, are the switches on during this problem?

yeah zammy all the wires and stuff have been replaced & the A/C has been unhooked this whole time .

Wow, seems like a doozie, Dennis.
When I get a vehicle with this kind of a problem, I like to elimate possible causes of the concern like you already have. (ie: swapping in known good components). However, without seeing the data being processed by the computer here it is difficult to give an exact suggestion, as there have been alot of good ones already. But I might have one.
You say you can get the engine to continue to run if you feather the accelerator pedal. Try running the vehicle on propane. How this is done - disconnect the fuel injectors & allow propane (from a common propane torch) to run into the throttle body as you start it up. If you can get the engine to run properly by adjusting the amount of propane added to the engine, then you have verified it is a fuel control issue & that the spark/ignition system is ok.
If you get to this point, it comes down to a process of elimination.
Verify good voltage (12 volts) to the vehicle & the computer system & computer sensors (5 volts). Just as importantly & most often overlooked is the grounds, to the vehicle & sensors.
Sounds like these have been done already.
The 3 biggest contributing factors in fuel control are: TPS, MAP & CTS. As mentioned previously in this thread the O2 sensor is also a large input/feedback to the computer in fuel control but only when warmed up. You can have a problem with any one of these sensors & have it cause your condition & not set a code. Having access to the data the computer is seeing is likely the key to figuring this out.
Are your terminals to the sensors ok? A spread terminal in a connector could be causing alot of grief. Check the 'pin drag' of the terminals.

Have you done any voltage drop testing on the ignition or fuel ciruits? It only takes a very slight increase in resistance to cause big problems.

couldn't get it to run on propane at all . we tried a few times . replaced the ignition switch with no difference . traced all the grounds again , nothing bad showing . can't really get a good reading on the voltage cuz its not running without feathering the gas . which causes fluctuation . plus the battery is a little low from all the starting . but we get 12plus volts & don't see any significant drops anywhere.

we really just don't know whats next .

Ok, I'll throw out a coupla wild a** ideas related to some quirky issues I've had lately.
If you are only getting 12+ volts off the alternator, something isn't right there, you should be getting better than 13.
On one of my jeeps had a quirky problem with it crapping out related to the alternator, pulled it had it tested, tested good, ran ok for a few days then started doing it again. voltage tested good in the car. replaced it, new alternator tested the same voltage as the old one, but no problems since. Only thing I can figure is the voltage regulator was having an intermittant problem. prior to all that I had checked all wiring and cleaned all terminals so it wasn't the a connection issue.

my other thought is the fuel pressure regulator. I'm having some problems with my adjustable pressure regulator. Twice I've started the van to have a weak coughing idle. I have a permanent fuel pressure gage installed. psi was around 6 psi. a bit of tweeking on the adjustment knob brought the pressure back up to 12 psi. The crankcase breather hose connects to the tbi directly behind the pressure regulator. when I replaced the original, he gunk built up on it was amazing. the tweeking appears to "clear"' the regulator. another thing i found on this last event at 4:30 am when I was supposed to be driving to the airport was that my map sensor hose, which connects right below this cesspool was a bit loose, I pulled it off to get at the adjustment screw for the pressure regulator and some oily crap spilled out of it. you aren't getting any codes so it's got to be be spark, fuel or vacuum. can't be vacuum, you'd have a high idle.

the crankcase breather port on my tbi is soon to get relocated a bit so as to not spray crap on the regulator at high rpm.
what were those gm engineers thinking?

Ok at this point we pretty much give up , don't know what else to do .

we're thinking the next step is ditch the computer & TBI for a carb , new dizzy & whatever else is needed to bring this 4.3 into the old school realm .
so if you guys could help us figure out whats needed to do this & aquire some parts as we're having to do this as cheap as possible .

we're gonna need a 4 barrel carb & the adapter plate to fit it to this manifold , an HEI distributor with no computer hookups ( if they even make such a thing for the 6 cylinder ) going to have to put a lock out switch for the torque converter , linkage on the carb for the TV cable from the tranny & a fuel pressure regulator to bring down the fuel pressure for the carb . a block off plate for the EGR valve .
is there anything i'm forgetting ???????

if anybody could help with exactly what carb & dizzy would be best for this project , please speak up the rest we can fabricate & figure out as we go .

dizzy .......http://store.summitracing.com/partdetai ... toview=sku

manifold.......http://store.summitracing.com/partdetai ... toview=sku

skippy wrote:Ok at this point we pretty much give up , don't know what else to do .

we're thinking the next step is ditch the computer & TBI for a carb , new dizzy & whatever else is needed to bring this 4.3 into the old school realm .
so if you guys could help us figure out whats needed to do this & aquire some parts as we're having to do this as cheap as possible .

we're gonna need a 4 barrel carb & the adapter plate to fit it to this manifold , an HEI distributor with no computer hookups ( if they even make such a thing for the 6 cylinder ) going to have to put a lock out switch for the torque converter , linkage on the carb for the TV cable from the tranny & a fuel pressure regulator to bring down the fuel pressure for the carb . a block off plate for the EGR valve .
is there anything i'm forgetting ???????

if anybody could help with exactly what carb & dizzy would be best for this project , please speak up the rest we can fabricate & figure out as we go .

Dan,
I can't predict when I will have the Ole Yellar swap done,but it is a 1985 with a carb and intake.It's a running engine with a rear main seal leak that I am currently driving while the LT is down with a bad fuel pump.

I appreciate the thought gary but we have to get this done ASAP .

skippy wrote:I appreciate the thought gary but we have to get this done ASAP .

Skippy,
One last thought to repair what you have.Check the connector between the computer and the engine harness by the top of passenger side dog house for shorts or bad pins.

All electrical connections have been checked, rechecked, and checked again.

Ok, as some of you out there are well aware, my 94 astro had given me some starting issues sorta like this in the past. I can't remember what my thread was, but it was a long one. i had tried everything on my van to get it to run correctly. did everything that you said you did. with one exception. this may sound funny, but it fixed my van, which is TBI. my problem was the coolant temp sensor........anyone remember now? LOL

actually, it wasn't the sensor itself, it was the plugin for it. it drove me nuts for literally MONTHS. I even had to add James to my MSN Messenger one day to give me some "live" help. (Which was VERY appreciated)

if you cts checks out, then check out the plugin. it certainly buggered my van up for a long time until i finally tracked it down.
Good luck!!!!!

goes from bad to worse !!!!!!!!!!!

on the good side of things we found it out to be a fuel problem . pump is going bad . found an injector backwards . it was running better & he was going to change the pump to getting back to 100% again , till this morning we're running after changing the injectors & it started knocking so now we have to find out why its knocking . sounds like top end , maybe a broken push rod or lifter but with out pulling it apart , who knows ??? we're hoping for the best but expecting the worst , thats just the fisher luck , it runs in the family !!! will let you know when we find out more . keep your fingers crossed for us .

if you've been crankin' on it for a while, and it has been getting gas, you may want to change your oil.