'91 S-15 4.3 shutters under load. This vehicle hasn't seen much action and this issue has some whiskers. I have replaced cap, rotor, wires and plugs. I checked compression a couple of years ago and all is good there, to the best of my recollection. Engine always starts like it was just parked this morning. Under load, it shutters. Seems to idle OK. I looked under the hood in the dark at idle and see no arcing. What should I check next?

Thanks

 

Do you think its the transmission or motor? Do the rpm's go up or down?

George

 

RPMs seem steady and I think it's the engine. It comes with a loss of power. Not a total loss, like one cylinder isn't doing its job.

 

I would look at (in priority order):

1. Fuel pressure, first key on engine off with leakdown. If that looks OK consider monitoring it when you experience the loss of power while driving with the gauge taped to the windshield.
2. Check your TPS sensor with key on engine off going through a few cycles back and forth slowly looking for glitches in live data
3. Check the strength of your coil output. That's subjective and harder to interpret for someone who does fix vehicles all day long but look for 1" of strong blue spark
4. Fuel trims at idle and 2500 rpm in park, then during a loss of power event
5. Look at your sensor values with live data on a cold engine key on engine off and see if the readings make sense
6. Get the full throttle 1-2 shift MAF sensor reading
7. O2 sensor graphs at idle and during a power loss event

George

 

I have an age appropriate OD reader but does the '91 provide all of those readings? I will check the fuel pressure, that sounds like a potential culprit. Does this model have a tap in it like the later models or will I need to make one?

 

I always forget when we have older trucks that they are ODBI. I am not familiar with what live data a 91 can provide and what type of scanner you need. Don't know on FP either. Never had a gen 1. If anyone with more gen 1 experience wants to jump in go ahead.

George

 

I am working on replacing the fuel filter but it doesn't want to let go. I'm about to quit trying to unscrew it and cut the tubing in front of it. To the rear, there is a rubber to steel connection about 15" behind the filter. That tells me that I should be able to patch it in front of the filter after cutting it out. I could either flare the tubing and install a coupler or patch it with rubber tubing of the quality that is behind the filter. I was surprised to see a rubber hose in this line but I guess it's OK. Would it be suitable to cut it clean and put a rubber tube coupling patch over it for reassembly?

 

Current status: Replaced plugs, wires, cap, rotor, coil an fuel filter. I have not rigged up a fuel pressure port yet. Still runs rough under load and has terrible fuel mileage. Fuel injectors seem to be functioning as per multiple youtube videos. My OBD reader is pretty primitive, it just taps out a morse code with the lights on the dash and the SES light blinks non-stop when it's inserted. Any ideas?

 

is it possible to just replace the whole rubber tubing section and connection to the fuel filter?

 

I got the front end of the filter to let go with some help from a buddy but the back end was pretty stubborn. I did unhook it from the rubber tubing and got it to give up the ghost in a a vise. That part is back together with no leaks (knock wood) and my problem persists. Some are telling me to check fuel pressure but is low pressure a possibility at this point? My injector cone is good and it responds well in the garage when I open the throttle. I am also experiencing bursts of power when all works for a second so I'm thinking something electrical is haunting me. I feel like fuel pumps work or they don't, not work but in a weakened capacity.