I recently purchased a 1990 GMC C1500. The truck came from the factory with a 350, I have not been able to verify that it still has the org engine though. Mileage is 28X,***. I bought it running poorly so I cant really give a history on it. Truck idles very rough and shakes significantly. I pulled the codes and got 33, MAP sensor signal high, low vacuum. I tested the MAP sensor according to the procedure laid out in https://troubleshootmyvehicle.com/gm/4.3L-5.0L-5.7L/how-to-test-the-map-sensor-1 . It worked fine, signal dropped under vacuum as it should, power and ground checked out as well. I changed the vacuum tubes to the MAP sensor, EGR valve, egr sensor. The vacuum line to my canister looks good and holds a vacuum. I also changed the hose for the PCV. Still running rough, still throwing Code 33. Very strong smell from the exhaust and very loud. Backing out of my driveway today it died twice. Backing out of my space at the grocery store it died as well. It will sit in the driveway and idle for a as long as I've let it. Sometimes it will die right after start up but once its idling, it will stay running unless I put it into gear. Brakes are not great. When I press the pedal that seem to react as expected, a little spongy but more or less responsive. However, when actually coming to a full stop they truck creeps further a bit further than expected.
I think it is "running rich" because of the smell and stumbling. I am, admittedly, not a super experienced mechanic so I could be wrong about that. If the MAP sensor is working and the vacuum tubes are as well, it suggests to me that the engine is producing low vacuum. This may also be causing the brake problem. The troubleshootmyvehicle.com article suggests that in my case I should test my cylinder compression and fuel pressure, but also mentions that the PCM may be fried. I doubt fuel pressure is the problem because it seems to be running rich, not lean. Also, prior owner replaced the fuel tank.
My plan is to check out the EGR valve and sensor next. If they check out or replacement doesn't solve the problem, I will check compression. If that checks out, I suppose I'll start looking at the spark plugs, wires, distributor. The wires look new, haven't pulled the plugs yet, and the shaft of the distributor looks corroded. There is a MSD box on the passenger side, but the best I can tell its not hooked up. The wires I see coming from it are disconnected.
I welcome any questions, criticisms, suggestions etc. I have a tendency to bite off more than I can chew so hopefully this isnt another example of that, lol.
I think it is "running rich" because of the smell and stumbling. I am, admittedly, not a super experienced mechanic so I could be wrong about that. If the MAP sensor is working and the vacuum tubes are as well, it suggests to me that the engine is producing low vacuum. This may also be causing the brake problem. The troubleshootmyvehicle.com article suggests that in my case I should test my cylinder compression and fuel pressure, but also mentions that the PCM may be fried. I doubt fuel pressure is the problem because it seems to be running rich, not lean. Also, prior owner replaced the fuel tank.
My plan is to check out the EGR valve and sensor next. If they check out or replacement doesn't solve the problem, I will check compression. If that checks out, I suppose I'll start looking at the spark plugs, wires, distributor. The wires look new, haven't pulled the plugs yet, and the shaft of the distributor looks corroded. There is a MSD box on the passenger side, but the best I can tell its not hooked up. The wires I see coming from it are disconnected.
I welcome any questions, criticisms, suggestions etc. I have a tendency to bite off more than I can chew so hopefully this isnt another example of that, lol.
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