Engine codes

[cdslyde]

Hello, I am new to this site. I have a 1989 K2500. Stock engine is a 5.7. I replaced the lower end with a 327 that appeared to be built. I had the stock heads rebuilt and cam is stock. Engine light was on before engine swap and don't know the history of that issue. After engine swap I am throwing code 33 and code 43, but only under heavier loads on the freeway. Some things I have already worked on include checking fuel pressure at inlet of throttle body at 11 psi, replaced air valve on throttle body, replaced O2 sensor, replaced tps, replaced distributor with new ignition module, new coil, new map sensor, and new temp sensor.
A couple questions I have are: Does the knock sensor somehow effect the map sensor, or vice versa? Where should I start? Could the lower end with the shorter stroke be causing these issues? I am stumped now so any help would be appreciated.

 

[WICruiser-97]

I am not an expert but I suspect that the smaller displacement lower end is not working well with the ECM. At higher loads and speeds the intake air flow generated by the smaller displacement is resulting in greater throttle opening and lower manifold vacuum that does not correlate well with the spark/fuel maps in the ECM. You may need to have the ECM reprogrammed to correlate your displacement.

 

[cdslyde]

Hello, I am new to this site. I have a 1989 K2500. Stock engine is a 5.7. I replaced the lower end with a 327 that appeared to be built. I had the stock heads rebuilt and cam is stock. Engine light was on before engine swap and don't know the history of that issue. After engine swap I am throwing code 33 and code 43, but only under heavier loads on the freeway. Some things I have already worked on include checking fuel pressure at inlet of throttle body at 11 psi, replaced air valve on throttle body, replaced O2 sensor, replaced tps, replaced distributor with new ignition module, new coil, new map sensor, and new temp sensor.
A couple questions I have are: Does the knock sensor somehow effect the map sensor, or vice versa? Where should I start? Could the lower end with the shorter stroke be causing these issues? I am stumped now so any help would be appreciated.

Does anyone have any advice on test procedures? What should the vacuum read at the map sensor? Would I have to stretch a vacuum hose all the way to inside the truck to get the reading during highway driving?

 

[Supercharged111]

You said the stock heads were rebuilt. Which stock heads? How much cam? You really need a scanner to be able to see what MAP and knock counts are doing real time. Could just be a junk MAP, but they're not a high failure item in my experience. Did you install the knock sensor on the 327?

 

[cdslyde]

You said the stock heads were rebuilt. Which stock heads? How much cam? You really need a scanner to be able to see what MAP and knock counts are doing real time. Could just be a junk MAP, but they're not a high failure item in my experience. Did you install the knock sensor on the 327?

The 5.7 engine heads that came off the original engine were rebuilt but similar to stock. The cam is the original cam from the 5.7 Engine as well. The history on this engine is that the original 5.7 crank shaft broke and thrashed the block, so we took the top end off the 5.7 original engine and used it on a 327 engine that was just a short block. This means we still used all parts from the original 5.7 engine other than the 327 block, crank shaft, pistons, and rods. Computer is still seeing the same original motor with same cam and heads, except a shorter throw on the stroke from the 327 crank shaft.

 

[cdslyde]

The 5.7 engine heads that came off the original engine were rebuilt but similar to stock. The cam is the original cam from the 5.7 Engine as well. The history on this engine is that the original 5.7 crank shaft broke and thrashed the block, so we took the top end off the 5.7 original engine and used it on a 327 engine that was just a short block. This means we still used all parts from the original 5.7 engine other than the 327 block, crank shaft, pistons, and rods. Computer is still seeing the same original motor with same cam and heads, except a shorter throw on the stroke from the 327 crank shaft.

Also, isn't a scanner tool just going to tell me what the voltage outputs are? If there is not correct vacuum input, then how would using a scanner tell me if it is a bad MAP sensor if the vacuum was not correct going into the MAP sensor? I am a newbie on all of this, but it just seems logical to start with know if the input vacuum was the correct amount first thing.

 

[Supercharged111]

Also, isn't a scanner tool just going to tell me what the voltage outputs are? If there is not correct vacuum input, then how would using a scanner tell me if it is a bad MAP sensor if the vacuum was not correct going into the MAP sensor? I am a newbie on all of this, but it just seems logical to start with know if the input vacuum was the correct amount first thing.

The scanner would display MAP in kpa (kilopascals), not volts. It may also display vacuum in another unit, but kpa is the norm.

 

[Schurkey]

MAP sensor shows PRESSURE, not vacuum. This gets old guys like me into trouble, since I'm more used to reading a vacuum gauge.

Listen to a weather report for your area. Barometric pressure is likely to be "about" 30 inches of mercury, or "about" 1000 millibars, or "about" whatever that works out to in Kilopascals, or troy ounces per cubit, or whatever.

When you connect the scan tool and look at the MAP sensor, ignition on, engine NOT running, you're likely to see "about" 30 inches of pressure, or "about" 1000 milibars, depending on how your scan tool is displaying pressure.

If the MAP sensor shows atmospheric pressure to a reasonable degree of accuracy, start the engine. You'll likely have considerably less pressure. 10 inches of mercury would be about right, but it can vary depending on how well the engine is running.

Download the service manual set for your vehicle, assure that the vacuum hoses--and everything else--is routed and connected properly. Then follow the diagnostic procedure for the two codes you have.

Did you unplug the "Set Timing" connector when you dropped that distributor in and did the initial timing adjustment? Did you plug the timing connector back in afterwards?

Yeah, you should probably get the computer re-tuned to account for the reduced displacement, but the O2 sensor may be able to adjust the fuel trims enough to get by for now--when everything else is working properly.

 

[cdslyde]

MAP sensor shows PRESSURE, not vacuum. This gets old guys like me into trouble, since I'm more used to reading a vacuum gauge.

Listen to a weather report for your area. Barometric pressure is likely to be "about" 30 inches of mercury, or "about" 1000 millibars, or "about" whatever that works out to in Kilopascals, or troy ounces per cubit, or whatever.

When you connect the scan tool and look at the MAP sensor, ignition on, engine NOT running, you're likely to see "about" 30 inches of pressure, or "about" 1000 milibars, depending on how your scan tool is displaying pressure.

If the MAP sensor shows atmospheric pressure to a reasonable degree of accuracy, start the engine. You'll likely have considerably less pressure. 10 inches of mercury would be about right, but it can vary depending on how well the engine is running.

Download the service manual set for your vehicle, assure that the vacuum hoses--and everything else--is routed and connected properly. Then follow the diagnostic procedure for the two codes you have.

Did you unplug the "Set Timing" connector when you dropped that distributor in and did the initial timing adjustment? Did you plug the timing connector back in afterwards?

Yeah, you should probably get the computer re-tuned to account for the reduced displacement, but the O2 sensor may be able to adjust the fuel trims enough to get by for now--when everything else is working properly.

Yes, I did unplug the timing wire when I set the timing at zero, then plugged it back in and reset computer.
Any advice on buying a scanning tool for this OBD1 truck to get started on the other recommendations?

 

[Schurkey]

Any advice on buying a scanning tool for this OBD1 truck to get started on the other recommendations?

This has been covered many times. Three examples:

GMT400 - Community Scan Tool

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Hey all, new to the forum and a long time chevy enthusiast. My father in law recently hired me to put his 96 3500 with a 5.7 back together after he had it sitting for the last 7yrs. He had the heads gone through and just moved onto the next project. I got the truck all back together and of...

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and many more if a person searched for them.