1995 K1500 TBI Surges Under Load after warmed up

Howdy, I’ve got a 1995 K1500 TBI with the 5.7 and I’m stumped. I’ve got this strange problem where after it’s warmed up it’s seems to surge and bog down and seems to vibrate if I give it more than give or take 30 to 45 percent throttle, not too sure why. At low throttle and slow traffic it does fine and shifts normally until I open the throttle up. When it’s still cool it drives fine, has plenty of power and I can open up the throttle and it feels good. But once it gets anywhere near warmed up the previous symptoms stated occur. I’ve replaced:
- Fuel Pump (about a year and a half ago)
- Both Coolant Temp sensors (about a year and a half ago)
- Cap, Rotor, Spark Plugs AND Wires (about a year and a half ago)
- K&N cold air intake (a year ago)
- Throttle Position Sensor (a year ago)
- Thermostat (6 months ago)
- Fuel Filter (Last weekend)
- Catalytic Converter AND o2 sensor (this week)
- MAP sensor (today)
- BOTH Fuel injectors and rebuilt Fuel Pressure Regulator (Today)
The truck also has a Radiator from a 454 Big Block, and the top fan shroud from the 454 I pulled the rad from. I live in Yuma AZ and it gets hot as hell here so I thought maybe it’s overheating or something but the temp gauge sits right where it should be unless I’m sitting in bumper to bumper at idle and then it’ll get a little hot, but as soon as I start moving around it’s fine. This problem began occurring about two months ago when I drove from Northern Nevada to Yuma (about 700 miles), broke the trip up into two days and I didn’t start to notice it till the end of the first day, and by the time I was 100 miles outside of Yuma it started to really become a problem. My heads just starting to hurt from this and so is my wallet, I’ve probably sunk way too much money into this thing in the last 2 to 3 weeks than I ever have so some help pointing to the right direction would be fantastic.

P.S I’m not throwing any Engine codes although last week when I was driving from San Diego (or, atleast, trying to), when I was going up the big hills outside the city I had literally no uphill power under load and it threw a code 44 (lean fuel condition) briefly and then I threw in the towel and pulled over. Hasn’t thrown a code since.

no magic bullet, scanner time.

you've had this problem for 1.5yrs? or did start more recently?

did you check fuel pressure?

Code 44 might be telling you something ....

Wiring short circuit to ground, fuel pressure low, MAP sensor, misfire, fuel contamination, exhaust system leaking, O2S/HO2S, ECM

The problem just started on that Drive out to Yuma about two months ago, before that I never had this problem but I started to notice it in the drive and it progressively got worse. I don’t have a gauge to check fuel pressure (and not entirely sure how to) but I imagine I can try and get one at orileys or Napa or something

since problem started 2 months ago, imo, you need to check all the parts you changed to make sure they are working correctly, especially, O2S/HO2S, misfire and Fuel system.

The service manuals can be downloaded and see if you can borrow the scanner from this site.
not sure on loan procedure.

First download service manuals from sticky thread above titled 88-98 service manuals for your application, look in fuel and emissions manual at symptoms should find something there to help. If more questions just ask and someone on forum will answer. If your egr valve is vacuum operated have you tried removing vacuum line and driving to see if difference, it only takes one tank of bad fuel to stop up or restrict a fuel filter which could also cause low power. Knowing fuel pressure and having access to fuel pressure gauge will be needed if trying to repair yourself for code44. Let us know and best of luck.

Sounds like it’s acting up once the ECU starts operating in closed loop mode. A scan tool would allow you to determine if this is the case. Don’t worry about connecting a scan tool to determine this, at least not yet, just hold that thought in your head.

EGR can occur after the ECU enters closed loop mode, and EGR takes place at part throttle conditions, so let’s keep that thought in mind. This is when you have symptoms. SO… Try disconnecting the EGR valve (unplug the connector), it would be an easy test, to see if performance / symptoms change. This will set the SES light, but ignore it.

FWIW: Excessive exhaust gas recirculation would cause a rich condition, inadequate EGR would cause a lean condition. Your code 44 might be indicative of this.

Otherwise, I’m wondering if it’s possible to force the ECU to stay open loop to see if the symptoms go away. If so, then we’ll know better where to debug. Disconnecting the ECT might be one way…

Back to the EGR: If, after disconnecting the EGR the engine runs better, you may continue to leave the EGR disconnected; it will continue to show the SES light (and probably set and maintain a code). You can totally disable the EGR, as I have done on my 1995 S10 4.3L, with a "tune" to the ECU. Otherwise, you can fix the problem; this may require a new EGR valve or simply cleaning the passages on the one you have. Let's worry about these details later, if they apply.

1998_K1500_Sub said:

I’m wondering if it’s possible to force the ECU to stay open loop to see if the symptoms go away. If so, then we’ll know better where to debug. Disconnecting the ECT O2 sensor might be one way…

Click to expand...

FIFY.

Overall, this truck is crying out for a scan tool and fuel-pressure test.

Schurkey said:

Overall, this truck is crying out for a scan tool and fuel-pressure test.

Click to expand...

The lack of symptoms during open loop operation really points away from fuel pressure, that's why I took the "EGR" tack.

My 1995 OBD1 S10 4.3L vehicles (I had two, now have one) seemed prone to EGR valve problems, that's reason #2 I took the "EGR" tack.

It's easy to test for an EGR problem as well, that's reason #3.

1998_K1500_Sub said:

Sounds like it’s acting up once the ECU starts operating in closed loop mode. A scan tool would allow you to determine if this is the case. Don’t worry about connecting a scan tool to determine this, at least not yet, just hold that thought in your head.

EGR can occur after the ECU enters closed loop mode, and EGR takes place at part throttle conditions, so let’s keep that thought in mind. This is when you have symptoms. SO… Try disconnecting the EGR valve (unplug the connector), it would be an easy test, to see if performance / symptoms change. This will set the SES light, but ignore it.

FWIW: Excessive exhaust gas recirculation would cause a rich condition, inadequate EGR would cause a lean condition. Your code 44 might be indicative of this.

Otherwise, I’m wondering if it’s possible to force the ECU to stay open loop to see if the symptoms go away. If so, then we’ll know better where to debug. Disconnecting the ECT might be one way…

Back to the EGR: If, after disconnecting the EGR the engine runs better, you may continue to leave the EGR disconnected; it will continue to show the SES light (and probably set and maintain a code). You can totally disable the EGR, as I have done on my 1995 S10 4.3L, with a "tune" to the ECU. Otherwise, you can fix the problem; this may require a new EGR valve or simply cleaning the passages on the one you have. Let's worry about these details later, if they apply.

Click to expand...

I’ll try this out and see if it makes a difference. I have had issues with my EGR in the past (also replaced this is as well last year) and about 7 months ago it randomly popped an EGR code and then went away… so maybe this is my problem. I’ll let yall know if this helps at all

So I tried unplugging my Vacuum line running to the EGR, didn’t notice any difference. I live on base out here in Yuma and there’s an auto shop so I’m gonna see if one of the technicians can help me figure it out as well. I have a good amount of tools in my truck, but no OBD1 scanner or fuel pressure gauge, so I’m going to see if the auto shop has either of those.