Questions for the professionals
dar24347
12-03-2008, 04:40 PM
Alright, the back story. I bought this truck (C1500 350CI 4x2 short bed standard cab) from the auction for about 1500 bucks with about 195,000 miles on it. After having the transmission rebuilt, new cap, rotor, wires, plugs, fluids, front and rear brakes, and shocks it was ready to go. After about a year of no problems i decided to add some umph to it with several modifications. I did so one at a time to hopefully help me figure out if anything went wrong along each step.
First I installed a header back exhaust system which comprised of:
1 5/8" primary 3" collector into a y pipe into a single cat, back to a glasspack.
That seemed to give it a bit more power and nothing really negative came out of it.
Second I installed a Holley 670CFM Throttle Body.
This is where the problems started. I confirmed there was no vacuum leaks and everything was hooked up properly. It started right up as if it had always been on the truck. While driving it around it had a flat spot if I mashed the throttle where it felt like the truck was starving for more gas. No cloud behind the truck or anything. After playing with the TPS the voltage was at .4V with the truck off key on. After speaking to a Holley rep who told me it should be at .65V, I went out and modified it to hit that voltage. That seemed to make it alot better but it doesn't feel right yet. I also installed a jet stage 2 performance chip slightly after the install, which made no change to the problem.
The problems:
1. It does not shift at the proper times all the time. If i mash the gas after say a right turn i nearly have to floor it just to get it to shift into a more suitable gear for acceleration. I am fairly nice to my truck but accelerating from 15mph to 40mph in 4th gear is a very slow process.
2. It takes several cranks to start it up after being off for a couple minutes. The starter sounds like its spining at full power but the voltage gauge inside the truck basically never hits 14, and whenever i turn on the headlights, the stereo, the heater, and a window or something where it draws heavy on the battery it drops down a chunk for each item I turn on.
3. The temperature gauge never gets to "running temperature". I have swapped the thermostat, the temp sensor, the fluid, and nothing had made it go above about 140 on the gauge.
The #1 problem has plagued me for almost 3 months and I am running out of ideas of what I can check to rule out. The fact that it is entirely random is confusing.
On a side note, when I first start the truck up its almost like 1 cylinder isn't firing for the first few seconds as it warms up. It's rather an odd feeling and I am not entirely sure that's what it is, but it only happens if the motor is cold.
Any help would be greatly appreciated, I am lost.
First I installed a header back exhaust system which comprised of:
1 5/8" primary 3" collector into a y pipe into a single cat, back to a glasspack.
That seemed to give it a bit more power and nothing really negative came out of it.
Second I installed a Holley 670CFM Throttle Body.
This is where the problems started. I confirmed there was no vacuum leaks and everything was hooked up properly. It started right up as if it had always been on the truck. While driving it around it had a flat spot if I mashed the throttle where it felt like the truck was starving for more gas. No cloud behind the truck or anything. After playing with the TPS the voltage was at .4V with the truck off key on. After speaking to a Holley rep who told me it should be at .65V, I went out and modified it to hit that voltage. That seemed to make it alot better but it doesn't feel right yet. I also installed a jet stage 2 performance chip slightly after the install, which made no change to the problem.
The problems:
1. It does not shift at the proper times all the time. If i mash the gas after say a right turn i nearly have to floor it just to get it to shift into a more suitable gear for acceleration. I am fairly nice to my truck but accelerating from 15mph to 40mph in 4th gear is a very slow process.
2. It takes several cranks to start it up after being off for a couple minutes. The starter sounds like its spining at full power but the voltage gauge inside the truck basically never hits 14, and whenever i turn on the headlights, the stereo, the heater, and a window or something where it draws heavy on the battery it drops down a chunk for each item I turn on.
3. The temperature gauge never gets to "running temperature". I have swapped the thermostat, the temp sensor, the fluid, and nothing had made it go above about 140 on the gauge.
The #1 problem has plagued me for almost 3 months and I am running out of ideas of what I can check to rule out. The fact that it is entirely random is confusing.
On a side note, when I first start the truck up its almost like 1 cylinder isn't firing for the first few seconds as it warms up. It's rather an odd feeling and I am not entirely sure that's what it is, but it only happens if the motor is cold.
Any help would be greatly appreciated, I am lost.
777stickman
12-03-2008, 08:18 PM
I may have missed it but, the year of this truck is?
dar24347
12-04-2008, 01:00 AM
1994. Sorry, with the massive text wall i forgot the simplest fact x.x
777stickman
12-04-2008, 11:14 AM
1st thing I would do is put the stock TBI back on and see what happens.
On the temp problem you need to hook up a known good gauge (manual) to see what it's really reading. This need to go into the drivers side head. I believe the thermostat should be a 190-195.
The tranny problem I can't help with.
On the temp problem you need to hook up a known good gauge (manual) to see what it's really reading. This need to go into the drivers side head. I believe the thermostat should be a 190-195.
The tranny problem I can't help with.
2000CAYukon
12-04-2008, 01:39 PM
Since he has a 4L60E trans, the TPS is critical for shifting and it sounds like the TPS on the new Throttle Body is not right. Like 777stickman said, try putting the old one back on.
//2000CAYukon
//2000CAYukon
jdmccright
12-04-2008, 01:42 PM
I'd suggest checking the fuel pressure, fuel pump, filter, and the pressure regulator. If you're not getting enough fuel into that Holley, the ECM will retard the timing to prevent a lean condition, resulting in power loss. Running lean tends to make the plugs run hotter, resulting in plug damage and increased emissions. And when the engine is detuned, it messes with the tranny shifting.
New TBI gasket set, regulator diaphragm, fuel filter, and EGR valve check & clean won't set you back much. You can also have the injectors sent out to be cleaned and flow tested for ~$50 if you don't mind being without your beloved truck for a few days.
I'm in the midst of refurbishing my own '95, so some of this I've done, some I'm waiting for a warmer day. But all of it is recommended on any refurb job.
Hope this helps!
New TBI gasket set, regulator diaphragm, fuel filter, and EGR valve check & clean won't set you back much. You can also have the injectors sent out to be cleaned and flow tested for ~$50 if you don't mind being without your beloved truck for a few days.
I'm in the midst of refurbishing my own '95, so some of this I've done, some I'm waiting for a warmer day. But all of it is recommended on any refurb job.
Hope this helps!
dar24347
12-05-2008, 02:01 AM
I'll try swaping the old TB back on in the morning and see if that sets it back to right. I don't have the tools to check the fuel pressure. What does a shop normally charge for that check?
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