Bought a 1995 Bronco with about 131k with a 5.0. It has 32" tires, a lift, cold air intake, and an "exhaust". It seems about every time I drive it while it's hot, it struggles. It will bog down at stop lights, trying to shut off, it will blow black smoke off acceleration and will start wierd. I've replaced coil, cap and rotor, plugs, plug wires, maf, iac, tps, icm, egr valve and sensor, oxygen sensor, fuel filter, and cleaned the throttle body. The temp sensor does not work on the dash and I haven't been able to read codes. The check engine sometimes comes on, sometimes I can turn the light on just by pushing the gas pedal down enough and it will turn off when I lift. The plugs aren't black and I'm not sure what else it could be. On cold starts it will be perfect, and once it stops acting up when it's already hot it often will run fine. Most of the time the truck will run fine, other times not. Any help is appreciated.

 

I would say try pulling engine codes and try to limit throwing parts at it, only makes it harder especially if a brand new part is bad. A good place to start is checking the timing with a timing light. Should be 10* BTC. After that you can always check the main things like fuel pressure with key in the on position and while running, checking to ensure you have good spark going to the plugs and possible even doing a compression leak down test on the cylinders. If all checks out it could very well be something electrical or computer related. Good luck and keep us posted on your findings

 

Just pulled the codes-
159-mass air flow sensor fault, above or below normal
334- egr closed valve voltage high

The maf is brand new so I'm going to try the old one and see if that helps with that code. As for the egr voltage code, I'm kind of lost, I'm wondering if it could the egr relay? Not sure if anyone has had this issue.

 

I cannot comment on the EGR code as mines removed altogether. There's lots of info on here about diagnosing EGR codes.

Can you send us a pic of the aftermarket cold air intake? It is possible that the meter is not getting correct flow, especially if it's throwing a code. Also, if its a conical filter, it must be oiless, otherwise the oil on the filter (if applicable) could be fouling the MAF sensor and throwing it off. I picked up a oiless conical filter at summit, and its even washable.

-Glaser67

 

Threw the old maf back on and it cleared up that code right away. If anyone could give me some advice on the egr issue, it's brand new but it's not motorcraft. Any help is appreciated

 

A broken vacuum line is often the cause of EGR problems.

 

The pressure regulator to vacuum diaphragm may be ruptured. Apply suction to the line that goes to the intake manifold to see if fuel is present.

 

agree with Paul on the vacume line....also IMHO scrap the CAI they are known for contaminating the MAF

 

CAI wont hurt the MAF, I have a cold air intake and my MAF is just fine. check for vacuum leaks, replace vacuum lines, and then start looking for leaks in the engine.

see how it runs when warm if you unplug the MAF sensor.

Also what brand is it and where did you get it? The reman ones sold at auto part stores are garbage and 90% are bad when they are sold.

 

The old maf is now throwing the same code, I can get a reman motorcraft on unless there is a better option. I will try to drive it with the maf unplugged and I will get back to y'all on that. Which vacuum line for the egr is most likely the culprit? Never tested vacuum before and I'm new to the emissions crap. Tempted to try to delete the egr completely.

 

"Runs bad when hot, blows black smoke, temp sensor doesn't work and cold starts are perfect."
Possibly the failed temp sensor is telling the computer the engine is always cold causing a rich mixture??