I have a 1990 Ram Van, 250B, 318, auto, with TBI. Within last 2 weeks it dropped mpg to about 7 and yesterday, the black smoke started. Huge puff upon downshift/acceleration and a flame backfire from pipe when revved at a higher rpm when parked. The backfire happens when I drop off the gas. Torn between fuel filter, injectors, and o2 sensor. Possible timing? Any ideas would help to get started. Oh, and my check engine light is constantly on because the voltage regulator is re-routed (to get past replacing a $400 computer). So, if you ask about the check e. light, I won't know.

It's also hesitating with a little throttle from idle... Almost to a cut off. The exhaust has a stronger smell to it... dirty, or rich. Hard to explain, exactly.

Forgive me if I ask or say something dumb as I am kind of an amateur. I can do basic maintenance (tuneups, oil change, blah blah) But, I'm sick of relying on others to fix my stuff.
Thanks.

 

Welcome to DF
I will move your post to the Ram Van section.

 

You can still get the trouble codes to see what is showing up besides the voltage code. That aside, it sounds to me like your time chain might've jumped a tooth. For flames to be coming out of the exhaust it would mean the exhaust valves are open at the wrong time.

 

The engine is running extremely rich which could be due to a bad O2 sensor or bad ecm. Unburned fuel can accumulate in the exhaust sytem and be ignited resulting in a backfire with flame. I would also check the vehicle for exhaust leaks.

Problems with the fuel pump or fuel filter usually result in a lean mixture or lack of fuel which will have very different symptoms than those you describe here.

 

You cat may have just given up its 9th life. I'd check there first. My van ran almost the same way when my cat was broken inside.
Good luck...

PS. If you do have a clogged cat -- why would that be...Just FYI if you have a clogged cat, you have another problem (usually) that caused the cat to fail, such as a burnt exaust vavle, cracked head, leaking fuel injectors, etc.

 

Several years ago I bought a 91 V8 dakota for my daughter and the guy was selling it because it started getting 8-10 mpg.He said it needed a tune-up.After I got it home on the trailer I found an extra PCM in the truck,and boxes for dist. cap,rotor,gas filter. He tried to tune it but never found the problem. I was letting it run one day with the air cleaner off and noticed a drip coming from the upper rear throttle body in the venturi area.I shut it off and noticed that where it was dripping from was directly in front of a vacuum hose that pushes onto the back of the throttle body. I pulled the hose off and it was wet with gas. The hose plugged onto the right rear of the throttle body and curves around to the left rear of the body to the fuel pressure regulator which bolts to the left rear throttle body.The diaphram was leaking in the regulator. I grabbed a used one in the bone yard and it's been running great for three years now. Normally the pressure regulator is connected to manifold vacuum. But on this Dakota it uses the vacuum that goes through the Venturi's instead.I thought someone may have connected it in the wrong place but the vacuum diagram sticker showed that it was connected correctly. I don't know if this is your problem but if you disconnect the vacuum hose from the regulator and it's wet inside you will definately be running rich.

 

Thank you all for the info. I've run the van very little this last year but picked up the work in July/Aug this year. This is what I've done. Replaced the MAP, PCV, fuel and air filters.. also new gas cap as the original was lost. Changed the oil but havent done a thorough tune up (needs it, btw, badly) The problem started again about 3 weeks after. Here are the codes I was able to pull: Remember, the voltage regulator is currently hardwired outside the computer, so some of these codes are expected.

12- Battery power to PCM disconnected
41- Generator field not switching properly
51- Right rear (or just) fuel system lean
46- Charging system voltage too high
51- (came up again)
then the 55 ending code.

When I checked the oil (changed Aug 8) it was BLACK BLACK BLACK and smells strongly of gas AND is heavy over the fill line. Removed the doghouse and it looks like there's fresh oil or gas that has leaked or sprayed.

New MAP may be defective. Will need to replace the computer. Any ideas are appeciated. Thanks!

 

Thank you UltraLite, btw. I'm checking those connections next.