87 tbi 350 popping at idle and running rich

[devildogcummins]

Truck starts up fine, at idle it will backfire out left exhaust pipe and runs rich, poor mileage. no codes. Truck has dual exhaust no cats. Did compression test and all are 168-176. Did tune up, plugs, wires, cap, rotor, ignition module, o2 sensor. all ac delco parts. no change, changed thermostate from 160 to 195, takes awhile to get up to temp but now once warm it idles with no pops but idles kinda low and rough. Acceleration is hit or miss, sometimes it pulls good sometimes sluggish. Cruises at speed fine. Has new fuel filter, going to test pressure tonight hopefully. Any more help would be greatly appreciated.

 

[Ricko1966]

First thing I'd do is a power balance test. If you are running equally on all cylinders,I'd test fuel pressure,map sensor,coolant temperature and air temperature sensors.

 

[Vbb199]

Whats the injector spray pattern look like?
Should be even, fine misted upsidedown cone with no dribbles. Shine a flash light at them and watch them

 

[gmbellew]

Whats the injector spray pattern look like?
Should be even, fine misted upsidedown cone with no dribbles. Shine a flash light at them and watch them

a timing light works well for this. the strobe effect helps.

and while the timing light is out, I'd disconnect the EST and check base timing to make sure it is at 0 deg BTDC (or maybe a little more won't hurt, but you don't want less).

 

[gmbellew]

the sometimes lack of power and sometimes fine makes me think about an intake manifold vacuum leak.

also check to make sure the EGR isn't stuck open.

 

[Octane]

I've had to take throttle body off and clean out dirt/ carbon from all ports.

 

[fast 99]

Check vacuum, if low or not steady will be rich. Popping in exhaust has a myriad of causes. From ignition misfire to loose valve guides.

 

[77Dmax]

Check the CTS. You'll need a scan tool that can read data. If its running "cool" it'll be pig rich, pop skip and have no balls.

 

[Ricko1966]

You can check it with a multimeter,same with the air temp sensor,and the map sensor.

 

[77Dmax]

True but it'll be difficult to do that while test driving. It's nice to graph the data and watch for abnormalities.

 

[Ricko1966]

True but it'll be difficult to do that while test driving. It's nice to graph the data and watch for abnormalities.

Sure but if he doesn't have an aldl cable and software,or a tech 2 etc he can't do that anyway. He can test the values on his sensors they don't even have to be installed. All he needs is a multi meter and a piece of vacuum hose. A vacuum pump and a pan of hot water would be a bonus but that isn't really a necessity. Take readings hot and cold,read the map voltage restricting the vacuum line and letting it open compare the readings.