'93 4.0 help

[sjranger]

Yea, there is definitely something going on somewhere that I just haven't seen yet.

Last night I messed with it some more and ran the truck with the MAF unplugged - made no real difference in the way it ran, but did throw the proper code. I proceded to unplug other sensors with the hope that one would be the culprit. In all, I tried unplugging the TPS, IAC, MAP, coolant temp, and the O2 sensors. At times it seemed the motor was more responsive but the backfiring on the down-rev was always present.

Are there any other sensors that I should try unplugging? Also, would the computer always throw a code if it was running in limp mode?

I have a reader and EVTM on the way but I'm thinking it something mechanical due to the lack of change when sensors were unplugged. If the weather holds out I'm going to do a vacuum check tonight and carefully check for any exhaust leaks. It is leading me to believe that maybe the injectors are a little clogged/sticking and causing it to run rich and ignite in the exhaust. Any thoughts?

As a side note, I found that the alternator is not charging, but I think this is an unrelated issue. Also, the VSS is not hooked up, but again this shouldn't be doing anything to cause these problems.

 

[feellnfroggy]

No change doestn neccesarily mean mechanical. I still think you need a brand new maf. Unpluggin will pinpoint the problem, but will not make the backfiring stop. That is beause it is running rich. It wont stop til the prob is fixed.

 

[sjranger]

Reman MAF didn't change much. Still getting occasional backfire at idle and visible black smoke and backfire when revving. The alternator issue is resolved, just a poor contact.

Engine vacuum seemed ok, about 20 psi with no needle movement.

Any ideas?

 

[Big Jim M]

Backfire out the back is a rich mixture.. Backfire up front is too lean of a mixture. Up front also could be a burnt valve.. but the idle would be terrible.
Big JIm

 

[sjranger]

I know its rich and that is why it is backfiring in the exhaust... I also know it is terrible.. The motor ran great prior to the swap so I'm sure whatever is causing this issue is probably a minor fix, I just don't know what it is. I'm just looking for suggestions

 

[feellnfroggy]

Maybe nothing is wrong. Maybe you just need a new tune. Maybe one of your sensors has just a little too much dielectric grease and isnt providing accurate readings. WHo knows.


You know my truck runs rich and there is no visible blakc smoke. Have your injectors checked, maybe one or more is stuck open and dumping excess fuel that way.

 

[sjranger]

Out of curiosity, does anyone know the acceptable loss of pressure is for the fuel rail? I hooked up my fuel pressure gauge today and it appeared to be zero... I hit the key one time and it went to about 33psi (5pm) By 9pm the rail pressure had dropped to 15psi. I have no visible leaks and the pump seems to work just fine while the engine is running. I am hoping this is a sign of a leaky injector, hence my running rich/backfire problems.

I will check again in the am and update you guys

Tomorrow I hope to hit the u-pull and grab some coolant temp sensors and some injectors and maybe some other sensors

 

[sjranger]

Sometimes you surprise yourself by the mistakes you make... Always make sure your plug wires are run properly!!

So yea, the reason why it was running so poorly was that I somehow ran the wrong plug wires to the driver side of the motor. Because the coil fires twice per cycle, it would still ignite the fuel in the cylinders some of the time and the remainder would go into the exhaust, causing the backfire....

Wow.. I'm embarrased..

Ohh well, runs great now, even better than when I brought it home in the ranger.

feellnfroggy, thanks for all your help, it was much appriciated. I'm sure all the MAF cleaning and such is why its runnin better now haha

 

[BlackBII]

Glad to hear you got it figured out!

After reading this whole thread, I was gonna ask if you made sure your plug wires were all correct...dang. Wish I woulda been on TRS over the weekend, could have helped you out.