MythicalRewards
Newbie
Hey everyone, I have an issue with my 1997 GMC Sierra C1500 with a 5.7 motor that's paired up with a rebuilt 4L60E. I've recently got the truck up and running from a bad distributor rotor and a distributor cap. While trying to find that issue, I've replaced the entire spider injector assembly with the electronic MFI design. I've replaced the timing chain and the cam and crank sprockets. And I also replaced the ignition coil module and the ignition coil a few months prior because the module quit on me. I know I've installed everything correctly, and I've placed all of the gaskets from all of those jobs. I don't think I have any obvious vacuum leaks and that's because I plugged off the throttle body plate, and then I vaped into the brake booster hose, and I didn't see any vape smoke come up, it held pressure.
The issue I'm having with the truck, is that the engine like to stutter and stall randomly. It's not completely random, it seems when it's under a load. For example, any time I turn the steering wheel all the way to the right, and push down on the brakes, the RPMs will drop real low, then start surging like it's wanting to stall out. It'll do this if I turn the wheel all the way to the left, but it seems to do it more often if I do it to the right. It'll also have a little stutter, like a sudden deep dip in power for a split second when I make a right turn or a left turn while going normal speeds, for example, like turn left at a stop light or something. And what's happened recently too, is that the engine will stutter while going straight. I'll be going around 45MPH and then I'll get a little jerk back multiple times in the span of a couple of seconds, the RPM will drop spike downwards and then jump right back to normal like nothing happened. Just the other day, I hit a bump in the road, and I suddenly lost throttle response, a couple seconds later, I shift it into neutral, and then rev it. It revs fine, so I put it back in gear and then I give it gas. It works fine, so then I try to floor to see what happens. The engine works up to like maybe 5000 RPM, and then it doesn't go past that. So I put it in park, check the codes, and it gives a transmission slipping code. Fast forward, I check the transmission fluid, and it's full. It smells a little burnt, but that's fine. Right after I clear the check engine codes, I hope back in, put it in gear, play the gears, and it shifts great. I've never had an issue the shifting before, I still don't to this day, and I even floored right after, and it shifted through the gears fine. So I'm thinking that sudden loss in power confused the computer and it thought it was slipping or something. That's so far all of the symptoms I've been dealing with.
The codes I'm getting for the truck are P0300 - which is a random misfire, P0103 - which is MASS AIR FLOW SENSOR CIRCUIT HIGH FREQUENCY, and that one is interesting because I've also seen the low frequency code pop up while also having the high code present as well. I've also had a fuel system trim lean code and a catalytic converting not efficient code, but those codes have been present ever since I bought the truck a year ago. I've also had a random misfire, but this is taking misfiring to a whole never level.
What I've done so far, is I've hooked up probes to the MAF sensor and tested it. I know it's better to have an oscilloscope or measure in Hz, but unfortunately, I do not have access to a multimeter with HZ on it, or an oscilloscope. With the key on, I proved the connector, and I've getting 12V for the power, a good ground, and the signal is 5V even. When I plug it back up and test the signal with the engine warmed and idling, the signal voltage sits at 4.45V. When I slowly rev it up, the voltage drops slowly which no sporadic variations. When I open throttle wide open, it drops fast. I don't see any problems with the reading. However, as far as I've seen, the voltage is supposed to go up, not down. That's the only issue I see with my test. I'm not sure if the trunk is different, but other GM cars around the 90s all go up, so I don't know. I've attached links to both of the two videos showing my test. Please excuse my squeaky belt. It's old and it squeaks a lot.
I'd really like to get this issue fixed. It's not hindering my daily driving, but I need some help before I load up the parts cannon and but a new MAF sensor. Any ideas anyone? What else should I test?
The issue I'm having with the truck, is that the engine like to stutter and stall randomly. It's not completely random, it seems when it's under a load. For example, any time I turn the steering wheel all the way to the right, and push down on the brakes, the RPMs will drop real low, then start surging like it's wanting to stall out. It'll do this if I turn the wheel all the way to the left, but it seems to do it more often if I do it to the right. It'll also have a little stutter, like a sudden deep dip in power for a split second when I make a right turn or a left turn while going normal speeds, for example, like turn left at a stop light or something. And what's happened recently too, is that the engine will stutter while going straight. I'll be going around 45MPH and then I'll get a little jerk back multiple times in the span of a couple of seconds, the RPM will drop spike downwards and then jump right back to normal like nothing happened. Just the other day, I hit a bump in the road, and I suddenly lost throttle response, a couple seconds later, I shift it into neutral, and then rev it. It revs fine, so I put it back in gear and then I give it gas. It works fine, so then I try to floor to see what happens. The engine works up to like maybe 5000 RPM, and then it doesn't go past that. So I put it in park, check the codes, and it gives a transmission slipping code. Fast forward, I check the transmission fluid, and it's full. It smells a little burnt, but that's fine. Right after I clear the check engine codes, I hope back in, put it in gear, play the gears, and it shifts great. I've never had an issue the shifting before, I still don't to this day, and I even floored right after, and it shifted through the gears fine. So I'm thinking that sudden loss in power confused the computer and it thought it was slipping or something. That's so far all of the symptoms I've been dealing with.
The codes I'm getting for the truck are P0300 - which is a random misfire, P0103 - which is MASS AIR FLOW SENSOR CIRCUIT HIGH FREQUENCY, and that one is interesting because I've also seen the low frequency code pop up while also having the high code present as well. I've also had a fuel system trim lean code and a catalytic converting not efficient code, but those codes have been present ever since I bought the truck a year ago. I've also had a random misfire, but this is taking misfiring to a whole never level.
What I've done so far, is I've hooked up probes to the MAF sensor and tested it. I know it's better to have an oscilloscope or measure in Hz, but unfortunately, I do not have access to a multimeter with HZ on it, or an oscilloscope. With the key on, I proved the connector, and I've getting 12V for the power, a good ground, and the signal is 5V even. When I plug it back up and test the signal with the engine warmed and idling, the signal voltage sits at 4.45V. When I slowly rev it up, the voltage drops slowly which no sporadic variations. When I open throttle wide open, it drops fast. I don't see any problems with the reading. However, as far as I've seen, the voltage is supposed to go up, not down. That's the only issue I see with my test. I'm not sure if the trunk is different, but other GM cars around the 90s all go up, so I don't know. I've attached links to both of the two videos showing my test. Please excuse my squeaky belt. It's old and it squeaks a lot.
I'd really like to get this issue fixed. It's not hindering my daily driving, but I need some help before I load up the parts cannon and but a new MAF sensor. Any ideas anyone? What else should I test?
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