Hi Everyone, I have a 95 GMC Vandura2500 with a fuel injected 305V8 and Auto trans, under 90k on it, it runs ok, idles a bit high, gets lousy mileagew like 7-9 mph City…Tends to cough fart of pop through the intake(?) when cornering or starting up an incline…turning the distibutor to adjust timing changed it a bit better…now it is warmer and its popping almost constantly, sudden explosion Pop! Pop pop pop couigh pop! loss of power, I know these have basic computers in these vans, I’ve been told they suck, no error messages last time i checked it…I thought maybe gas tank venting ? Or a sucky computer…I am old school so am not up on changing sensors…I have changed the plugs, coil, wires, cap, rotor, starter, belt, battery, oil, filters (Not Gas Filter)…I bought the usual cheap gas and this started, it was fairly warm and the longest trip on the warmest day yet…It would not stop popping…I am disabled and out of work at present…What would you suggest as the cheapest thing to try next? I will be adjusting the timing as I drive, a nice benefit of Van ownership to see if thast helps…Please send in your thoughts…Thank You !
Go back to the gasoline octane that worked before; maybe, even a notch higher.
Have you checked the timing? That’s done with a timing light and a hand operated vacuum pump, isn’t it? I’m sure the repair manual will tell you.
The misfire could be lean misfire. Have you changed the fuel filter? Have you checked the fuel pressure with the engine under load (in Drive, 2,000 rpm)?
With the 305, you might even have a bad timing chain. Changing the timing to make it run better is the usual thing to do when the timing chain slips. Those engines had no chain guides so the wear was greater than some of the newer design engines. The high idle may be a sign that something else could be the cause. Somebody should check for OBD 1 codes just for grins.
Thanks…Seems much better today now that the recent gas fill up is laregeyt gone…maybe some bad gas made things worse…not sure…but its better by far after a run today…with some pops…than before…I haven’t done the timing check the right way no…I will try to find out if there is an inline fuel filter I missed I did one of them, thanks again 
Thank You…I will see if I can get a cheapo check for codes done…my biker buddies have the gear but they are too far away in gas money for me to take the ride…Do you think the Chain would have slack ? The van still has less than 90K on it ? Thanks Again,
You can get a free code check at Autozone.
Oh ? Great ! Thank You !!!
Those chains always had slack like you would not believe. That’s why we never reused them. You couldn’t tell a year old one from a six year old one.
NO, you CAN’T get a free trouble code reading at Auto Zone, for a 1995 model year key, to get the flashed codes. For a 1996 (and later) car or light truck—yes.
You can check the timing chain wear by marking the crank pulley, the position of the distributor rotor, and turning the crankshaft just a little bit clockwise, and then, ccw. The amount the crankshaft moves, before the rotor moves, indicates the wear in the timing chain.
Cam lobe wear is another possibilty. You can measure how high the tip of the valve stems rise, as you turn the engine by hand, to get cam lobe wear indication.