Gremlins in my 1989 C1500 - 350 5.7

[Malibuskier]

Issue #1 – I have an electrical short somewhere and I think it is in the steering column. One of the symptoms is the speedometer works sporadically. About 40% of the time the gauge does not function until a rap to the plastic face of the gauge panel is applied. The second symptom is significantly more worrisome. While driving (at random times, seemingly when I hit a bump but not definitely) the entire system shorts out for a second or two. The engine stalls (SES, Brake, Seat Belt lights go on), the radio shuts off, A/C or Heater shuts off and anything else electrical that happens to be on shuts off. Everything resumes normal operation after the short hesitation, but it is weird. It is starting to happen more & more frequently. Any ideas?

Issue #2 – I recently blew a head gasket in the same vehicle. After replacing both heads (due to cracking), putting new head gaskets, new plugs/wires/distributor cap, new thermostat, new hoses, adjusting the rockers and setting the timing something is still not right. The truck runs nice at idle, but as RPM’s increase things begin to happen. Under acceleration I hear a ticking noise that sounds like an exhaust leak but I have checked all exhaust connections and can’t find any. The only thing I have not done is lay under my truck and have my wife blip the throttle to check the Y-pipe connections. The truck vibrates slightly indication a rough condition and feels like a dead spot in the firing order at higher RPM’s. At approximately 45-55 MPH another phenomenon occurs. It feels almost like a surging effect, with a fairly noticeable thud tied to the surge. Coupled with all this is terrible gas mileage (roughly 8 MPG vs. 13-15 that it was). I have pulled all the plugs and they are all dry and a light brown, which I think is normal. Compression is 165-170 on the driver side head and 170-175 on the passenger side head. A visual inspection of the wires has revealed nothing obvious. I am not loosing any coolant as far as I can tell. There is no water in the oil or oil in the water. I am not sure what to check and need help. Should I pay a mechanic to do a diagnostic check on the truck?

I don’t know if these two are kinked or separate so I put them together. Sorry for the length…..

Dave

[2000CAYukon]

For issue #1, could be a bad ignition switch.

For issue #2, How did it run before you replaced the heads? It almost sounds like the valves are too tight. How did you adjust them? 1 turn past zero lash?

At 45-55 is when the TCC locks up. It is possible that you are having some lockup issues. This can be valve body issues or the TC itself; however, you need to figure out the rough condtion first.

//2000CAYukon

[BowtiePowerhouse]

all i can say is hunt exposed wires the best u can. sounds like something is periodically grounding out shorting the circuit. maybe lucky, loose fuse? lol

cup your hand over the end of a dowel, broken broom handle, or another solid wooden object. place the other end in various suspect places. when the sound is more pronounced then u know the general area of the issue. not a solution no but an easy way to locate the issue.

screams vacuum leak.

also, 45-55mph regardless of rpm = not engine, transmission. everything inside the engine itself for the most part is predictable, what happens at 45mph at 3000rpm in 3rd gear should happen at 30 mph at 3000rpm in 2nd. If u are just engaging 4th gear around there or OD, maybe one of the solenoids is sticking or something... <--- not a transmission expert.

[Malibuskier]

OK, so here's the latest. Found a pretty vaccum leak in the intake manifold (good call Bowtiepowerhouse!), so at the moment I have the intake manifold off and have stopped for the night. I took the opportunity to take the throttle body off and replace the gasket, as well as give the manifold a good cleaning. Tomorrow I will put it all back together and see how it goes. I hope this cures the majority of the problems. As for the surging at 45-50 MPH, let me clarify a little bit. It is an automatic truck with no tack. The surging only occurs after about 30 seconds of constant RPM. If I were to put it in first or second and drove I'm pretty sure the surging would occur. At the moment, it happens at 45-50 MPH because I have about a 5 minute drive to and from work at that speed. That bit of information probably would have helped.

Dave

[BowtiePowerhouse]

put it all back together, see if it still surges. ill be shocked if it does. good luck bud. make sure u get that gasket on there nice and snug, no remnants of the old one . lol

[Malibuskier]

Having been down the gasket road before, I spray the area with carb cleaner and then hit it with a brass wire wheel in the cordless drill! That way I get a nice clean surface and just to be sure I wipe it down with Acetone. I hope this clears everything up. I'll post results later today.

Dave