94 Chevy k2500 lack of torque

[hunter4ever12]

So I have a 94 Chevy k2500 with the 350. I bought it used with 180k on it but it runs like a top doesn't burn oil, doesn't even have a leak. I do keep getting the occasional IAC code... Which I've tried to correct but have had no luck. I have replaced the IAC, checked the wiring harness(no issues there) and even tried to adjust base idle(the cap for the idle adjustment screw was missing when I bought the truck) I can't seem to get the base idle down to what the instructions say(I "seat" the IAC then unplug it and screw the idle adjustment screw all the way out and still can't even come close to the 600rpm mark.) I am beginning to wonder if my throttle body blades, and/or my throttle body bores aren't worn out enough that, no matter the adjustment, the idle is going to be what it is, I believe this because I've smoke tested for vacuum leaks and have found absolutely none.) Also I have somewhat of a voltage issue, it could be the gauge though... My voltage fluctuates between 14-12 fairly rapidly, and the hotter the operating temp gets the lower the voltage gets, so at operating temp it reads more like 12-10 volts....either way these are what I believe to be secondary issues, but I thought I would give for relative information....

Anyways the issue at hand is I have very little to no low end torque/power. It takes for ever to accelerate and reach higher rpms(I can floor it and it is no different acceleration wise if I give it half throttle.) As well as the fact that I have a 4:10 rear end so I should have loads of torque, especially, over a 1500 of the same year(which I have driven/owned before) and that's simply not the case in my experience. Let me put it into perspective.... When trying to power brake it( I know that's bad on the tranny/torque converter...but for testing purposes) with the pedal to the floor it will not go past 1800 rpms and won't spin the tires no matter how hard i try. Something is wrong, it's not throttling up like it should like any other 350 I've ever owned does. I'm not quite sure why, or where to start. I thought maybe a plugged cat... But I took out the o2 sensor and drove it and there was absolutely no change. I just want the power that I am being robbed of to be restored. Thanks for the help.

[Schurkey]

Idle too fast
1. PCV system leaking, or have the wrong/failed PCV valve which allows too much air flow?
2. Failed charcoal canister or plumbing allowing too much air flow?
3. Failed or incorrect TBI base gasket? There's a bunch of different gaskets, and some WILL NOT SEAL with certain throttle bodies.
4. Scan tool--look for commanded idle speed
5. Worn throttle body

No low-end power
1. Scan tool--look for knock sensor activity/spark retard, short- and long-term fuel correction, O2 sensor output, Coolant temp sensor reading, etc.
2. What is the fuel pressure UNDER LOAD?
3. When was the last tune-up? Plugs inspected/replaced, plug wires tested/replaced, distributor cap/rotor inspected/replaced, ignition timing checked, etc.
4. Cranking compression test/leakdown test/cylinder balance test--worn rings, leaking valves, retarded cam timing due to worn timing chain
5. A failed torque converter sprag will kill low-rpm acceleration while making little difference at higher speed.

In both cases, you will want to figure out the voltage problem first. Test voltage AT THE ALTERNATOR to see if it's steady and regulated to an appropriate voltage (about 14.2 although it can vary some.) If the voltage is good at the alternator, you need to repair the connection to the voltmeter in the cab. This may mean fixing corroded connections for the entire power supply to the cab--but I'd start with the bus-bar above the AC/Heater system on the firewall.

My '88 has fine voltage at the alternator, but the gauge reads about two volts low (but reasonably steady unless the turnsignals are on.) Cleaning the contacts at the bus bar helped, but didn't entirely fix the problem.

[hunter4ever12]

Originally Posted by Schurkey

Idle too fast
1. PCV system leaking, or have the wrong/failed PCV valve which allows too much air flow?
2. Failed charcoal canister or plumbing allowing too much air flow?
3. Failed or incorrect TBI base gasket? There's a bunch of different gaskets, and some WILL NOT SEAL with certain throttle bodies.
4. Scan tool--look for commanded idle speed
5. Worn throttle body

No low-end power
1. Scan tool--look for knock sensor activity/spark retard, short- and long-term fuel correction, O2 sensor output, Coolant temp sensor reading, etc.
2. What is the fuel pressure UNDER LOAD?
3. When was the last tune-up? Plugs inspected/replaced, plug wires tested/replaced, distributor cap/rotor inspected/replaced, ignition timing checked, etc.
4. Cranking compression test/leakdown test/cylinder balance test--worn rings, leaking valves, retarded cam timing due to worn timing chain
5. A failed torque converter sprag will kill low-rpm acceleration while making little difference at higher speed.

In both cases, you will want to figure out the voltage problem first. Test voltage AT THE ALTERNATOR to see if it's steady and regulated to an appropriate voltage (about 14.2 although it can vary some.) If the voltage is good at the alternator, you need to repair the connection to the voltmeter in the cab. This may mean fixing corroded connections for the entire power supply to the cab--but I'd start with the bus-bar above the AC/Heater system on the firewall.

My '88 has fine voltage at the alternator, but the gauge reads about two volts low (but reasonably steady unless the turnsignals are on.) Cleaning the contacts at the bus bar helped, but didn't entirely fix the problem.

As far as the fast idle goes, I know its not a gasket or plumbing related ive checked... Could be the charcoal canister, or the wrong pcv(previous owner installed wrong one possibly) but I don't believe it to be either. I think something is actually wrong with the IAC/IAC circuit itself... I'm leaning towards a bad ECM. I say this because with my AC turned on my idle drops and the IAC does not correct it and bring it back up. Therefore when running the AC I do not ever get the IAC code. The only time the code comes up is with the truck warmed up, Ac off, and in park only(even with ac off in drive at a stopped idle I will not get the code.)

Now on to the other issues, first off, I solved my voltage issue last night i, I found the ground strap that goes from the head to the firewall was burned in half, replaced last night, and much better.

As far as no low end power, i do not have a scan tool, I do have an obd2 scan tool but not an obd1... I know they make adapters that will plug into an obd1 and then the other side has an obd2 outlet to plug the scan tool into... Do those work? I do not have experience with them. If yes great, if no, what is the cheapest but best bang for your buck obd1 scan tool?

Fuel pressure under load fluctuates between 12-13 psi... At idle it's about 15-16 (I did do the quarter mod to the FPR to bump it up) but I do also have a throttle body spacer, salad bowl, and injector spacers, so with the added air flow I'm still not quite confident my fuel pressure is where it should be.

As far as tune-up, I did a complete tune up on the truck when I bought it (roughly 6000 miles ago) plugs, wires, cap, rotor, air filter, fuel filter, tranny flush and new filter, coolant flush, I did pretty much every you can think of maintenance wise when I bought it... That way I have a starting point of my own for maintenance intervals.

As far as compression test etc, I haven't done anything I but can, I just assumed(I know assuming is bad ha-ha) that because i am not burning any oil and there is little to no blow by(I checked this by taking the oil cap off the valve cover with it running and it's not puffing smoke like it would if it had excessive blow by) I assumed my compression is good.

Also, you mentioned the torque converter, I have my suspicion that could possibly be my problem but do not know for sure. Is there any sure way to tell/check it without replacing the converter itself and either seeing improvement or not. I do know that my converter is locking up correctly, so that's functional at least(I tested this by cruising at hwy speed with my right foot on the gas and then tapping the brakes with my left. The rpms jump up as soon as I tap the brakes so I know the converter is locked until I tap the brakes then it unlocks) one thing I will mention about that test though is after doing that the converter will not lock back up unless I completely let off the throttle then get back on it again. That may be normal i don't know....but in my previous pickup 97 F250 Powerstroke, it the converter would lock back up on its own without letting off the throttle after performing the same test. Something else that I am unsure of is if the converter is fully locked or properly locking when performing the test on my 94 k2500 the rpm jump is very minimal(maybe 100 rpms) in my Powerstroke the rpm jump was more like 300-400 rpms. That could just be the difference in transmissions/pickups, or I could have a slight Lock up problem with the TC in my Chevy I'm not sure which.

Lastly one last thing that leads me to believe it could be torque converter/drivetrain related is, when driving down the road if I slowly give it more gas it seems like there is little to no increase in speed or rpms, it really takes stomping on the peddle to about 3/4 throttle before it will downshift and pick up speed. I know on the 94 there is no TV cable and that the downshifting is controlled by the ecm so I'm thinking there could possibly be a problem with the ECM or something in the drivetrain, any thoughts on that individually and or regarding my other issues?