92 c1500 5.7 bucking hard/loss of power

[amizzly]

Hey everyone,

 

I am having issues with my 92 c1500 5.7l. I made this account because I desperately need help from people who know more about these things than I do. So let's start.

 

The first thing you need to know is that I have a weird truck. Someone who had it before me said they had the CTS (cooling temperature sensor) go bad, and the temperature gauge doesn't work. Their fix for it? They hooked a manual toggle switch up to the ECU so that they can flip the switch on when the engine is cold, dumping more fuel, and flip the switch off when the engine warms up, giving it a leaner air/fuel mixture. I believe the issues I have may have something to do with this.

 

Where the problems start: The truck will idle fine if it is COLD with the toggle switch on, and will idle fine when the engine is at normal temp with the switch off. If it's cool but not cold, it will idle rough (rpms almost die and the jump back up to 1500 then down again) with the switch off, and die with the switch on. I figure this is simply because this switch doesn't give it a healthy air/fuel mixture because it's not adjusted gradually by the computer; instead it's simply rich (on) or lean (off).

 

Next, when I back out of the driveway, it does fine (I slightly ride the clutch out and back out) Then I go to first gear, and let off the clutch slowly, and give it a tiny bit of gas, just like any other manual tranny. Now, if I have a perfect or near perfect launch, no problems occur. But, if I am in a rush, or simply not paying enough attention (I'm rather inexperienced) the truck will buck. Normal right? Well this thing doesn't buck once or twice.. As I continue to accelerate through first, it will buck HARD. enough to make the front end dip like 6 inches repeatedly. If I don't let off the gas, I slow down and it continues to buck even when I'm not on the throttle. If I do let off the gas, it will either clear out and stop, or will keep going. If I turn it off and crank it over again and roll into first, the problem totally clears out.

 

Assuming we have the bucking problem out of the way, I will accelerate up through first. Sometimes this is smooth, sometimes there are dead spots, and sometimes there are lots of dead spots. I shift into second. Sometimes the shift is smooth, sometimes it kind of jerks forward, and sometimes it jerks HARD. I accelerate through second, and this is where the worst dead spots are as far as acceleration. It doesn't act like the gears are slipping or something, but rather like it is having trouble firing properly and is losing power. Once I accelerate past 2.5k or 3k, it runs like a dream. Shift into 3rd, and all problems stop almost 100% of the time. Very rarely it will jerk into third or fourth, but usually these shifts are clean. I figure this is because by now the wheels are moving plenty so that they are enough to keep the engine spinning alone.

 

I will almost guarantee this is NOT a transmission issue. My clutch doesn't smell, it disengages and engages properly, and the tranny NEVER grinds except if I don't go into a different gear before reverse, which I'm told is pretty normal. Another clue that this isn't the transmission is that when it bucks, the higher RPMS that it jumps to are the normal ones, and when the rpms drop, it is due to a loss of power. This I have tested by trying to floor it when I'm bucking, and it really doesn't do anything except kill the sometimes engine and I have to restart it. If it were a tranny problem, it would just go out.

 

Can someone please tell me what's going on here? Is the toggle switch the cause of this? Bad TPS? Something else? All three? I'm happy to provide pictures, videos, or further explanation for anyone who wants to take this problem on with me. Thanks so much in advance.

 

Also, I will include a video with this post as soon as it uploads to youtube.

 

EDIT: I should probably include that it NEVER backfires. If I'm in neutral and the truck is warm, the engine sounds VERY strong and does not have any problem picking up RPMs when revving. It sounds like a beast, and when it's warm it rarely misses in idle.

 

Video:

Skip to 4:30 to see it buck hard in first gear.

[mike94silverado]

Wow... I never understood why people rig things like that...

 

 

Sent from my iPhone using Tapatalk

[copperheadcreek]

Is that a parking brake light on? If so might disengage that. First thing I would do is get rid of the switch and and actually replace the coolant temp sensor.

 

Sent From My Moto X Using Tapatalk

[txab]

Is that a parking brake light on? If so might disengage that. First thing I would do is get rid of the switch and and actually replace the coolant temp sensor.

 

Sent From My Moto X Using Tapatalk

+1 for starters