Engine Upgrade Questions

[guzzler96]

I have recently made some engine mods and it appears that I am not getting the full results that I expected.

Vehicle is a 1993 C1500 Chevy pickup with the following:

5.7 L (350) 4L60E Auto. Transmission

Stock Heads

TBI

The following mods were made:

280/480 Cam

.040 over 11:1 Dome Top Pistons

Blocked Deck .010

61# Per Hr. Fuel Injectors (2)

Summit Shorty Headers

Hypertech 123122 ThermoMaster Power Chip

I also installed a 160 degree thermostat, but not the Hypertech PowerStat.

Truck is just not running right. I bought the Hypertech chip because after the mods were made it seemed as though gas mileage dropped off and the truck idled poorly. After installing the chip it still idles poorly, but also surges at idle from about 600 or 700 RPM'S up to about 1100 or 1200 RPM'S. I have driven truck with an Autoxray EZ Scan 6000 connected and have printed out data from the ECM at idle, but don't know exactly what I should be focusing on.

Anyone help would be greatly appreciated.

 

 

Thanks,

guzzler96

[Wingnut]

I would suggest giving PCMforless a call. He can program a custom PCM for you, taking your mods into account.

 

But with a bigger cam, I would imagine that you would surge a bit at idle...But I'm no expert in that particular field either.

[sstruck383]

The main thing is the chip. When I built my 383 TBI, the chip has to be tuned right. Also, with TBI you can not put a huge cam in it. It makes the MAP Sensor go crazy. The max Turbo City and other people recommend is 204 on the intake and 214 on exhaust duration. Even with my 383, I can only use that much cam, I make can make it to a 210/214 but it would be close and the Map sensor is very sensitive to cam adjustments.

[BOFH-Z71]

I had a 90 C1500 that we finally had to rip out that POS TBI setup and just throw a carb on there. It's a PITA to get that computer to like any large cam at all. I had Performer RPM Heads, 650 4BBL Carb, and 282/288 .510/.520 cam in there and it ran really good. I would eat local 5.0 Mustangs alive racing them around town. Also had a prob keeping my 700R4 in 1 piece.. finally got tired of messing with that truck and sold it to get a stang, didn't like that, sold it and got a TA... 3 yrs later I'm here with a Z71...

[knez]

I used to own a 95 gmc 5.7l 4x4 with same problem after I built the motor up.It would surge often but not all the time put a scaner on it showed everything fine.Finally narrowed it down to bad egr valve which I don't believe will throw a check engine light.Also check throttle position sensor.