1990 GMC K1500 No Uphill Power Part 2
 

Truck is a 1990 5 speed 4x4 1/2 ton 350 TBI with 20,000 on a gm crate motor.
No catalytic converter and most everything on the engine replaced atleast once or more.
It had a 165 thermostat in it and no error codes even though the spark knock sensor wasn't hooked up.It was replaced.
I put a 192 degree thermostat in it but never had a chance to drive the truck until today.
On the highway at 70 mph I shifted into 5th gear and the truck felt rough then popped through the throttle body and threw error code 43.
The temperature guage inside the cab is also bouncing all over the place now.It will read 210 then bounce to 165 then back to 210 then to some other number.
I drove it for about an hour and it seems to run okay when running it through the gears hard but after a gear change and lower rpm it seems to run rough then it cleans up.
I am going on a 14 hour trip saturday and am willing to shotgun a bunch of parts if necessary.
Give me a list.
Lynn

Re: 1990 GMC K1500 No Uphill Power Part 2
 

It sounds like the truck is running out of gas, or running out of spark.

In you other post you never resolved the fuel pressure issue to my satisfaction.

In one place you said it had 10 pounds pressure and in another place you said it did not drop below 9.5 pounds pressure.

My experience has been, if everything in the fuel system is in good condition, then the fuel pressure runs near the high end of the spec. When a vehicle is closer to the bottom end of the spec, it seems like further testing reveals that the pressure drops way below spec at times. The TBI system needs constant pressure to run well. If the pressure drops at times, it causes drive-ability issues.

Just because it has a newer fuel pump does not mean it is any good. There are many poor quality pumps be sold the fail before the warranty runs out on them.

With the fuel pressure regulator spring you put in, the fuel pressure should be running to high.

With the misfire problems, and popping back through the TBI, the ignition system is suspect. You said you put in a cheap distributor you don't trust. Did you try new plug wires? Distributor cap? How about the coil? Have you tested to see how strong the spark is?

Another possibility I always think of when engine pops back through the intake is, does it have one or more camshaft exhaust lobes that are getting flat. I have run across flat cam lobes on GM crate motors that were spotless inside with no sludge, and perfectly clean.

You need to get rid of major runnning problems before working on the code 43. The code 43 can be caused by pinging do to low fuel pressure, or many other things.

Here is a link to his other thread, for those of you wondering what was discussed.
http://67-72chevytrucks.com/vboard/s...d.php?t=561411

Re: 1990 GMC K1500 No Uphill Power Part 2
 

ChevyTech
I appreciate all your help with this beast.

On the fuel pressure I haven't tested it with the new spring just the new fuel pump assembly so I will retest it on tuesday after my trip.
I don't have a fancy large faced gauge with big numbers widely spaced I have a gauge that one would normally see mounted on a fuel log or hood.

I pulled the 192 degree thermostat out today because after putting a new connector on the temperature sending unit it held steady at about 220 degrees.

My gauge in the dash uses very large increments.

I should also say it stumbles at low rpm rather than it misses.I am not real good at describing it over the internet but it feels like it cleans up as the rpm increases but just off idle its rough.

I will do some new parts and post back on tuesday.
Lynn

Re: 1990 GMC K1500 No Uphill Power Part 2
 

Okay big mistake by running it without any thermostat at all.It ran so rough I ended up putting a newspaper inside the grill to get a little heat in the motor.

I put in another new distributor cap and rotor today and no joy.I was going to run fuel presure again but it started raining.The plugs and wires are 3 months old but they are also the 3rd set on this motor.

It ran best with the 165 degree thermostat and never letting the rpm drop very low.

I parked it inside and will do the fuel pressure test again in the morning after everything dries off.
Lynn

Re: 1990 GMC K1500 No Uphill Power Part 2
 

Okay I liked the young lady at the parts counter so I bought new wires and plugs and still no joy.If I am on it it runs okay but if I am coming on a onramp and stab the throttle I have no usable low-end.

I re-installed the 165 thermostat as I need to use the truck but will buy one at around 180 degrees on sunday.I still haven't re-checked the fuel pressure but it has never dropped out of spec so far.

Now for a couple quick questions.

Can I run solid core wires on this thing if I don't care about the radio whining?

And how much power will the stock type 5 speed manuals take.The tranny in it is out of a 95.
Lynn

Re: 1990 GMC K1500 No Uphill Power Part 2
 

You can, but it will cause problems.

It needs a 195 for the system to work correctly.
The truck set a code 43.
A code 43 is an electronic spark timing code. A code 43 can cause such a lack of power that it can make the vehicle totally gutless. This could be a large part of the problems this truck has. My guess is the truck has multiple problems. If you don't go at this with a logical plan, and take care of what the system needs instead of trying to circumvent problems (fuel pressure, T-stat, solid wires) then you may as well stop now, and I can spend my limited time helping someone else.

Code 43 can be a very hard code to find the cause of, if it is getting set at a time other then the self test, when warmup is reached. I have talked about code 43 before and you can search my user-name to find posts on this topic.

Low Fuel pressure is a very common problem, and you should check it.

The 1990 HM290 was the first design of what is known as the Getrag, and was weak. As for the 1995, it depends on which trany it is.

Re: 1990 GMC K1500 No Uphill Power Part 2
 

ChevyTech
I put a 192 degree thermostat in the truck and it was reading 220 degrees on my guage.As these trucks go through heads like a drunk goes through beer I didn't want to hurt another set.

My thought on the solid core wires was I have replaced the wires so many times now would they be sturdier or an upgrade? I can read into your response that the answer is no so I won't waste the money.

The fuel pressure is in spec but I have yet to retest it after installing the TBI kit.

When I last drove the truck the service engine soon light came on for about a minute but when I checked it had not stored any codes.

I will buy another thermostat on sunday at 192 degrees and re-check the fuel pressure again.I just don't want to crack anymore heads.

You have any ideas on why the 165 runs at 165 all day long and the 192 runs at 220?
It sounds lean to me.
Lynn

Re: 1990 GMC K1500 No Uphill Power Part 2
 

GM gauges are not high quality.
When a GM gauge does not read right it should be tested for accuracy before believing what its reading.
You should test the engine temp with a infrared thermometer.

I Agree.
Fuel pressure is a common cause of a lean condition.
The code 43 can be caused by pinging from a lean condition.
Another thought on the code 43 is if you run the TBI trucks cold, they run richer then they would at a warmer temperature. This causes carbon build up. The carbon build up raises the compression ratio, which can cause pinging. Carbon build-up on the valves can drastically affect the the flow in and out of the cylinders affecting the power the engine can produce.

The fuel pressure regulator spring is what controls the fuel pressure. If you replaced the spring with a stronger spring the pressure should be higher.
If the pressure is not higher, it points to a weak fuel pump.

Re: 1990 GMC K1500 No Uphill Power Part 2
 

ChevyTech
Put in another 192 degree thermostat and re-tested the fuel pressure again.Took pictures but here is what I got that was not on camera.
O PSI until key turned on then 4 PSI.Once started 12.5 PSI at idle and when cruising.Pressure drops to 10.5 pounds when mashed to the floor when I run out of cam and throttle body as it noses over on the top end.I don't have a tach.
When the key is shut off pressure drops quickly.
I will run it on wednesday and keep a kitchen thermometer with me to see how the temperature gauge compares.When shut off I could hear the coolant overflow tank girgling so I suspect it is close.
When I try and accelerate on a cold motor it feels like 20 degrees of timing is pulled out of the motor and after reading your responses on code 43 I think the spark knock sensor is doing me wrong somehow.
I can hear no audible knock/ping at all.
Lynn

Re: 1990 GMC K1500 No Uphill Power Part 2
 

Great gauge and photo.

The pressure should be able to hit the spec during the prime.

Try to prime it, then turn the key off for a few seconds so it can prime again, the see what pressure it hits the second time you prime the pump without starting the truck.

Some of the TBI units have a bleed hole that drains off the pressure as soon as the key is shut off, so don't worry that the pressure drop when the key is turned off.

12.5 PSI is good but it should not drop off when you accelerate. This system needs steady fuel pressure to run right. Something is wrong. My guess is, the pump is the problem, or the hose is leaking in the tank.

I suggest only using OEM (Original equipment manufacturer) fuel pumps. I have seen so many pumps from other manufactures fail in the warranty period or just after the warranty is up that I suggest only using an OEM pump.

If you are shopping around, only get an AC Delco or Delphi pump.

Here is some more for you to think about on the code 43.
What many manuals will not tell you is that a code 43 can be set by something loose rattling on or in the engine. Lifters, cam, rod, crank and piston noises all have the potential for causing false knock signals to be produced.

The Knock sensor contains a piezoelectric crystal which causes a voltage to be produced. Loose components on or in the engine can cause the knock sensor to create a voltage and the system may interpret this as pinging. The system retards the timing because it determines it is pinging. The timing can be getting retarded without ever setting a code.

Loose torque converter bolts can cause a false knock signal to be detected.

Re: 1990 GMC K1500 No Uphill Power Part 2
 

ChevyTech
The fuel pump assembly still has 10 months on its warranty.Should I just replace the pump with a Delphi or would you swap out the assembly hoping to get a better one?
Is the fuel pressure supposed to drop a little while at full throttle or is it supposed to stay rock steady.I ask because before I went through the TBI it held pretty steady at around 10 pounds.

On the code 43 should I be buying something while I am doing the pump again or should I hold off until the fuel pressure is solved?
Lynn

Re: 1990 GMC K1500 No Uphill Power Part 2
 

The son of a friend on mine had two fuel pumps fail under warranty from the local auto parts store and asked me what is going on. I convinced him to cut the fuel pump open instead of turning it in for warranty. We then compared the impeller from the auto parts store pump to an impeller from the original factory pump. The factory pump impeller had about twice as many veins (fingers). It took no more talking to convince him to go buy a quality pump. They owned the truck several more years and never replaced the pump again.

The fuel pressure on TBI trucks should not fluctuate.

My guess is the new regulator spring brought the pressure up a bit, but the problem was a weak pump. Most springs being sold do not match the stock spring and will raise the pressure a few pounds. If you replace the pump with a quality pump you may find you need to change the fuel regulator spring back to a stock one, if it is a spring designed to raise the pressure a little over spec.

Fix the fuel pressure, and the code 43 could go away, if it is caused by a little pining from a lean mixture, from low pressure.