1993 B250 Van
After running for 20 miles the van would begin to lose its ability to accelerate. It would bog, pop, and spit when trying to increase speed, mostly when over 30 MPH. After following this as well as other forums I've embarked on the following odyssey to correct the problem. I first removed the catalytic converter which contained nothing but rocks and replaced it with a straight pipe. No change so I changed the fuel filter, re-routed the ignition and spark wires and discovered that the crankshaft position sensor wasn't bolted down. Still no change except the problem doesn't seem to require the engine running 20 miles anymore. It will bog down much sooner. So, I've now replaced the speed sensor, O2 sensor, and the throttle position sensor and cleaned the IAC.

The engine starts, idles, and runs great, but it doesn't want to accelerate unless done very slowly or after stepping on the gas if I back off a bit it seems to find its power. Otherwise, it speeds up very slowly and if applying too much pedal it will pop and backfire in the engine compartment.

Thanks in advance for any ideas or suggestion cause I'm about out.

 

If the O2 sensor was downstream of the CAT and you have removed the CAT, it's possible that once the van warms up, the O2 is not sensing the change. Just a thought.

Look up your van TSBs here for your year. Some will apply directly while others will apply for the diesel trucks. http://dodgeram.info/tsb/0_old_ix.htm Under group 14, Fuel, there are issues with the fuel pump delivery system.

Pop up a year like 1994, because sometimes a TSB may apply to your year. 1994-1/2 is when the Magnum engines came on the scene.

TSB 18-03-93A 92-93 3.9L Sag, Hesitation Or Rough idle http://dodgeram.info/tsb/1993/18-03-93.htm

TSB 18-02-93 92-93 V6, V8 Throttle Body Idle Calibration Check http://dodgeram.info/tsb/1993/18-02-93.htm

 

Thank you for the reply. This van is a conversion and sold as a 94 however it's really a 93.

The O2 sensor was/is pre-cat

There is no idling problem whatsoever, it is an acceleration problem that used to require that the engine be hot but as I've sought a solution, the problem happens much sooner than before and only under load. Revving in the driveway is no problem.

I was unable to find anything else relevant to the problem in the TSBs aside from the repairs done so far.

Could a fuel pump deliver the wrong amount (an excess) of fuel? When applying the gas I have better results if I back off a little or it might bog down or backfire.

 

Test your TPS for any erratic readings as you open the throttle and also test the fuel pressure. Let us know the results of your tests.

 

Doing wife projects today, will do the suggested tests in the morning. TPS is new yesterday. On a possibly related note, fuel is seeping from the check valves on the fuel rail while the engine is off. Don't know if that's a symptom or not.

The problem is getting more prevalent. It used to require me to run 20 miles before I could produce the problem. Later I found it to be after 13 miles, now it seems it will do it within minutes of starting. Something is failing and I've picked all the wrong targets so far, but I must be getting close.

 

Well took it to a reputable mechanic and he is stymied as well. He tested the TPS and fuel pressure and found them to be within specs. His best guess is the computer but is unable to test without swapping mine for a known good one.

Before going that route, I'm wondering if there is something else. Some sensor or something that should tell the spark plugs to fire faster? From my amateur perspective it seems that the pedal gets pressed, extra fuel is made available, but the spark isn't arriving on time, its frequency doesn't keep up with the additional fuel. At idle and at speed she is smooth, only when accelerating is there a problem.

Thanks again for pondering along with me.

 

Perhaps the spark is weak due to a failing coil.

Perhaps the spark is timed wrongly.

The 2 wire coolant temp sensor is one thing that tells the computer to advance the spark. On mine I am supposed to remove the cts connector when shining a timing light on the harmonic balancer.

I can adjust my timing on my'89 by spinning the distributor. I do not know if this is feasible on your model year

 

I can adjust the timing as well. In fact now that I think about it, one Dodge mech after finding the crankshaft position sensor was not secured properly did adjust the timing by rotating the distributor cap ~ 1/16 turn clockwise. I not sure why he came to that conclusion but I think that may be when it began to perform poorly at colder temps rather than only at normal operating temp.

I pick it up again this afternoon and will investigate the CTS.

 

Check your spark plugs wires to see if any of them have sharp bends or are tied in knots, effectively slowing down the electrical flow to the plugs.

 

The mechanic found the fuel pressure to be 35 - 40 PSI and the new TPS to be within specs. So I have now replaced :
O2 sensor
TPS
Speed Sensor
IAC (cleaned existing)
Re-routed spark plug wires
PCV valve
Re-bolted the crankshaft position sensor into place (it wasn't bolted)
Changed oil and filter
Changed trans filter and fluid

and the problem continues to worsen.

Once warm there is *******ly no acceleration. It can be achieved by slooooowly applying the gas, backing off when it starts to bog and before it backfires and being very patient. Within about 1 minute I can be at 30 MPH and a minute later 40. I can't be sure but I think I won't be able to go much faster than that. Before it's warm it runs great and has always started and idled fine.