HELP .1987 v1500 runs rough under load

[nickdean]

My 1987 v1500 roughs very rough under load but not at idle. At idle it revs up fine but when I put it in gear to drive it stalls and runs rough.it doesnt die but just falls flat on its face. I replaced all the gaskets in the throttle body. The idle air control, throttle position sensor, map sensor, coolant sensor, threw some Chinese injectors in it. No change so put the factory back in. Plugs,wires,cap,rotor, stator, and ignition control module. Fuel pump, fuel filter. Cleaned all grounds. Alternator is pretty new. And I had the timing checked.

 

[Ricko1966]

My 1987 v1500 roughs very rough under load but not at idle. At idle it revs up fine but when I put it in gear to drive it stalls and runs rough.it doesnt die but just falls flat on its face. I replaced all the gaskets in the throttle body. The idle air control, throttle position sensor, map sensor, coolant sensor, threw some Chinese injectors in it. No change so put the factory back in. Plugs,wires,cap,rotor, stator, and ignition control module. Fuel pump, fuel filter. Cleaned all grounds. Alternator is pretty new. And I had the timing checked.

How and when did this problem start?

 

[nickdean]

For a long time now it would intermittently run a little rough while driving but always came out out of it. I just checked fuel pressure and it held at 12 at idle, while reving, and while tryng to power break. How ever on a cold start at high idle it runs a lot better

 

[Ricko1966]

Is there any chance crossed #5 and 7 plug wire. It is a very common mistake.

 

[Rusty Nail]

i vote bad pick up coil
replace distributor

 

[Snoots]

Vacuum leak?

 

[1STLS1]

Throwing parts is time consuming and expensive and you changed everything already. Another vote for verifying the plug wires are on correctly. I have made this mistake myself.

I would have the air cleaner lid off, somebody in the driver seat, lightly power braking to the point the issue starts and spray some carb cleaner in the throttle body, your adding fuel. If it cleans up, it's lean, if it runs worse, it's rich, no change, it's electrical. Start troubleshooting from there.

Keep your hands and face away from the throttle body and I would suggest having a fire extinguisher handy just in case it backfires

 

[gmbellew]

For a long time now it would intermittently run a little rough while driving but always came out out of it. I just checked fuel pressure and it held at 12 at idle, while reving, and while tryng to power break. How ever on a cold start at high idle it runs a lot better

if it runs better cold than warm, the biggest change is when it is warmed up, the ECM is using the O2 sensor to adjust fueling in "Closed loop"

could be the O2 is getting flakey, or could be it has bad data for some other reason (plugged cat, misfire, etc) and the O2 feedback to the ECM is making it adjust fueling incorrectly.

guessing you dont have any sort of scanning capabilities for OBD1?

I think if you unplug the O2 sensor and drive it will throw a check engine light but the open O2 should force it to stay in open loop. might at least help rule some things out.

 

[nickdean]

I double checked plug wires. I've sprayed starting fluid all around throttle body, intake, and any vacuum lines with no change. I haven't tried spraying in throttle body yet while power braking. I did however have someone power brake it while i watched injector spray and it seemed fine. But while doing so the truck ran terrible and died it was at full operating temp then. No I dont have a scanner but I jumped terminal a and b and the only code I got was the three number twelve codes which I believe is its normal test.

 

[gmbellew]

when you had the timing checked, did you check it with the EST wire unplugged? timing should be 0 with it unplugged. start truck, warm it up, unplug EST, check timing with a light on no 1 wire, turn engine off, and reconnect EST.

 

[gmbellew]

next thing id check is the ECM ground by the thermostat housing and check all the ECM connectors at the components to make sure the connectors are good and the sensors look ok where the connectors plug in - IAC, TPS MAP, ICM, O2 sensor, EGR solenoid, coil, CTS.

might also check your battery cables for corrosion.

after that, you will have to get some scanner capability or get the multimeter out and backprobe sensors and make sure they are behaving properly- TPS, MAP, CTS would be the big ones to check. make sure the voltage is where it should be for the conditions. the emissions and drivability manual in the reference library will be your friend. there are tables that have temp vs voltage, manifold pressure vs voltage, TPS voltage vs throttle position (.5-.9v at idle, >4v at WOT, smooth change in between).

if you haven't replaced the O2 and dont have a scanner to check it, I'd just get a new ac delco one and put it in.

 

[nickdean]

Yes i unplugged the est wire when checking timing, ground by thermostat was cleaned and looked over. i cleaned battery cables and replaced the ends when I cleaned all grounds. I have looked over all connectors on everything i have replaced. I also put all old sensors back on one at a time to make sure i didn't get a bad sensors. I just went and bought a 02 sensor so I will try. I did unplug it and try it and it ran the same.

 

[gmbellew]

plugged exhaust or maybe the fuel pressure cant handle the engine load are the next things that come to mind.

did the check engine light come on with O2 sensor unplugged?

 

[nickdean]

Update. Yes engine light came on with o2 sensor unplugged. While trying to power brake and spraying starting fluid in throttle body the it ran way better and spun the tires. So with fuel pressure holding at 12 and new fuel filter. Whats everyone's though on what it could be. Fuel pressure regulator? Could the fuel pump allow to much fuel to return but hold pressure?

 

[nickdean]

Also i unplugged tps sensor started it, then it would power stall for 10 seconds, then it started to run rough and backfire. Which is probably because it was unplugged