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]

Glad I'm carbed. Enuff trouble

 

[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.

 

[77Dmax]

You're exactly right, but that should be a ballpark figure. Its much more valuable to read it in real time as it's happening. I turned wrenches for a long time. Lots of these momentary faults, or "hiccups" can only be found through graphing the data. One good bump and the sensor loses continuity or it has a dead spot in its travel. It's hard to recreate the environment under the hood while driving on the stove top. But you are correct with a CTS. So many ohms equals X degrees, and you can read it with a meter all day.

 

[Ricko1966]

You're exactly right, but that should be a ballpark figure. Its much more valuable to read it in real time as it's happening. I turned wrenches for a long time. Lots of these momentary faults, or "hiccups" can only be found through graphing the data. One good bump and the sensor loses continuity or it has a dead spot in its travel. It's hard to recreate the environment under the hood while driving on the stove top. But you are correct with a CTS. So many ohms equals X degrees, and you can read it with a meter all day.

I turned wrenches for a long time too 40 years give or take. You're right if it's intermittent he's probably not going to find it with a meter and hot water. The map sensor he maybe able to make glitch just by applying and releasing vacuum.If a sensor has failed,a resistance test will catch that. But long story short yep,until he gets some way to data log he should just give up and not try simple stuff he can do.

 

[gmbellew]

Even the data logging on the OBD1 is such a slow data report out rate that you can still miss small hiccups. I think it is just barely than 1 data a point per second being reported, even though the system itself uses data at a much more rapid speed.

 

[77Dmax]

I turned wrenches for a long time too 40 years give or take. You're right if it's intermittent he's probably not going to find it with a meter and hot water. The map sensor he maybe able to make glitch just by applying and releasing vacuum.If a sensor has failed,a resistance test will catch that. But long story short yep,until he gets some way to data log he should just give up and not try simple stuff he can do.

You are making this a pissing contest amigo. There is more than one way to skin a cat, and your methodology can easy give false results. It is what it is.