Hesitation at low to mid rpms, and voltage drop from a/c compressor

[Jacob Parris]

Alright so a few weeks ago on my way home from work, I noticed my truck running really sluggish from red lights unless I held it wide open. It’s a 95 k1500,5.7 4l60e with 137,000 Miles. In park or neutral it didn’t have any problem at idle but reverse or drive it would idle close to 500rpm and if you put any strain, such as turning the wheel, it would drop lower and often stall completely. So far I have replaced the fuel filter and swapped the IAC with one I had sitting around, and ran some BG 44k through he fuel. And still no change. From idle to almost 3500 rpm the truck feels like it has no power at all until you get out of second gear then it seems fine. While all of this is going on, I noticed the problem is worse with the AC compressor or headlights on. Any extra electronic draws power below the 14 volts and the turn signal drops and raises with each flash. It’s no major draw but with the headlights on, turn signal going and the AC compressor on it nearly drops to 12 volts. To address this problem I replaced one of the ground straps that I noticed was broken, and still nothing. Can somebody give me some more ideas on where to start to fix both of these issues. They both came at the same time so I’m guessing they’re correlated. Thanks yall

 

[Schurkey]

Does the alternator charge properly? IS THE ALTERNATOR REAR BEARING STARTING TO SEIZE?

I had one of the CS130 alternators on my '88 K1500. The first-generation CS 130 (Not the 130D) were known to lock up the rear bearing due to overheating the rear end-frame. I don't know what alternator is on your '95

I was driving home from work, the engine had less and less power, and the voltmeter was dropping. When I stopped for gas, the engine stalled and I couldn't get the engine re-started--it was seized and the starter couldn't turn it. The alternator was totally locked-up. I had to pop the serpentine belt off the alternator to get the truck to run--but then I had no power steering or water pump action. I drove away from the gas pump and found a nearby parking place, and changed alternators.

'Course, there's a pile of other potential problems--failed transmission, failing injector, failed engine sensors, engine problems such as flat cam lobes, broken valve springs, etc. Until I hear different, I'm saying it's due to low system voltage, a failed alternator of whatever cause.

FIX THE VOLTAGE PROBLEM, then connect a scan tool, look at the data stream. What is the commanded idle speed vs. the actual idle speed? Is the coolant temperature reasonable? O2 voltage swinging properly? Short- and long-term fuel trim numbers look normal?

 

[Gramps]

Check your fuel pressure. I’d guess the fuel pump is weak probably running 8-10psi vs the 12 it’s “supposed” to be. Just enough to run but wont make power.

 

[ram1220]

How old is the battery and alternator? Have you had them tested? Also check and make sure there isn't any corrosion on the battery cables themselves. Even under the sleeves. My 90 Sierra 5.7l did the same when the cables were corroded under the sleeves. Replaced cables and problem solved.

 

[Jacob Parris]

Does the alternator charge properly? IS THE ALTERNATOR REAR BEARING STARTING TO SEIZE?

I had one of the CS130 alternators on my '88 K1500. The first-generation CS 130 (Not the 130D) were known to lock up the rear bearing due to overheating the rear end-frame. I don't know what alternator is on your '95

I was driving home from work, the engine had less and less power, and the voltmeter was dropping. When I stopped for gas, the engine stalled and I couldn't get the engine re-started--it was seized and the starter couldn't turn it. The alternator was totally locked-up. I had to pop the serpentine belt off the alternator to get the truck to run--but then I had no power steering or water pump action. I drove away from the gas pump and found a nearby parking place, and changed alternators.

'Course, there's a pile of other potential problems--failed transmission, failing injector, failed engine sensors, engine problems such as flat cam lobes, broken valve springs, etc. Until I hear different, I'm saying it's due to low system voltage, a failed alternator of whatever cause.

FIX THE VOLTAGE PROBLEM, then connect a scan tool, look at the data stream. What is the commanded idle speed vs. the actual idle speed? Is the coolant temperature reasonable? O2 voltage swinging properly? Short- and long-term fuel trim numbers look normal?

The battery reads 12 volts with the truck off, and 13.8 while running. After putting a new IAC in it’s gotten better but still stalls under a load. I’ve checked grounds but still not convinced that they couldn’t be an issue. I’m going to test fuel pressure this week.

 

[Jacob Parris]

Check your fuel pressure. I’d guess the fuel pump is weak probably running 8-10psi vs the 12 it’s “supposed” to be. Just enough to run but wont make power.

That would cause it to die under a load too if I’m not mistaken. It’s running fine-ish. Still stalls if you don’t have your foot on the gas. And recommendations on a fuel pump if that’s what it ends up being. I plan on staying stock, but it has a full exhaust. I’ve read to upgrade to the Vortec pump but I feel like it would be overkill for my goals.

 

[Gramps]

No need for the vortec pump that is way more pressure than you need.
Oreillys part number E18001 should be around $50. Rated at 12psi and 40gph. A little bump over the stock 12psi/20gph. It’s enough to run the 300hp tbi motor I just finished - I’m sure it’ll be dandy for your purposes.