Blazer cutting out on highway
 

Hello all, new to the forum. I come here today seeking some answers to problems with my 1996 chevy blazer. I just got back from a trip last night that found the truck running very poorly. At highway speed in order to keep her around 65-70 I had to put my foot into the pedal hard otherwise the truck would lurch and stumble unbelievably badly. Additionally, when I would get into it to get her moving up to highway speed black sooty smoke would pour out of the exhaust pipe along with a wicked rich gasoline smell. My check engine light is on but has been on for over a year with no issues. This has happened one other time but it cleaned itself up within a couple of minutes. Both times however, I had the truck running at highway speed for several hours and stopped at rest areas or a gas station and shut the truck off. When I returned to the vehicle and returned to the highway the issues of stumbling began. My first inclination is a crapped out TPS. Has anyone else dealt with this or know the remedy for it? I read somewhere that people were finding issues with the MAF sensor in the air intake tube and that cleaning it alleviated the issues. I am going to hook the truck up to the OBD2 code scanner later tonight and dump the trouble codes. Anyone with any suggestions please chime in. Thanks in advance.

Sorry double posted

Hi MJKH, do you know why your engine light has been on for more than a year? What trouble codes do you have? What codes are new, and what have trouble code have you had for a long time?

Black smoke = rich mixture; so TPS is one thing to check. Also pull the EGR valve off and clean it and the passenges in the intake. Just do not let the carbon chunks fall further into the intake.
Very helpful to know what code has been set.
Age of distributor cap/rotor, plugs, wires???
Air or fuel filter changed when?

Any chance there is water in the fuel tank?

Just passing along some suggestions for you to think about.

I'm going to run the codes tonight.

The distributor cap/rotor, plugs, and wires are all probably pretty old. The truck has been in the family for about 5 years and I haven't changed them (they need it!)

Air filter I will replace

Fuel filter, tank, and fuel pump are all less than a year old.

El_Beautor Now that I think about it, the check engine light shut off briefly after it started screwing up and then came back on. Probably dropping a new code. I will post the codes here later tonight

Went and bought an OBD2 scanner. Pulled a 300 code for random/multiple misfires. When I looked at the freezeframe from the code, I saw that the code was collected at highway speed and that the long range and short range fuel %s were WICKED high (hence the black smoke). Took a ride down the highway with the live feed reading and she was running wicked rich still. I stopped at a rest stop and cleared the code to shut the engine light off. When I got back on the highway, and got on it hard to get up to speed, the black smoke was gone and it was no longer sputtering and spitting. I'm now suspecting an issue with the cap, rotor, wires, and plugs that are misfiring that is causing the vehicle to go into "limp" mode. I'll drive the truck to work tomorrow and see if the light comes back on or not.

The only other thing I noticed that seemed amiss were the O2 sensor readings. A friend of mine told me that the O2 sensors should output about .45 volt and hover in that range plus or minus .1 volt. All four of my sensors fluctuate between .100 and .800 volts at idle and while in motion. I don't know what the range is supposed to be on this vehicle. Anyone?

black smoke + p0300 = leaky fuel regulator/ spider injector, however fuel trims "should" be negetive not positive. If it's richening the mixture could be a bad maf or o2. Confusing

and o2's are supposed to bounce back and forth and not hover, in a perfect world they would but this world isnt perfect. Your o2's should peg in one direction when the black smoke is going on tho.

My friend mentioned the spider injector might be leaky. Would that be an ongoing issue or could it pop up randomly?

Do a fuel pressure and leakdown test. There's a guide on how to do it here on the Forum. Follow it and you'll be able to determine if the injector assembly is leaking.