Nate1647545505 Posted December 10, 2003 Report Share Posted December 10, 2003 Hello, Im helping a buddy rebuild his 1998 GMC 2500 with the 5.7 (detuned LS1?) motor. We replaced the cam with a more suited towing cam (Comp Cams 54-412-11), did a full rebuild, all new sensors, etc. The top of the block was shaved due to some damage from a blown headgasket, the block itself is still to spec. Exhaust is 2 Flowmaster 40 series, universal Cats, and Flowtech headers. I have a scan tool that keeps pulling the P1345 CKP/CMP - Crank Posistion and Cam Posistion when the timing marks are dead on! We have replaced the pickup plate and are now waiting on a new sensor. The interesting thing is, its running 9 degrees advanced constant. The Cats and headers glow after a stroll around the block. The truck has no pickup until 30, but once it hits 30 it takes off like a mofo. The truck stays in closed loop mode even at WOT. Everything reaches operating temp as should. Just wondering any ideas about what's causing the lean condition, hoping it is just the sensor... Any ideas welcome, and what data does this engine use from its O2s? all four? front two? I'm just use to the 3800 V6 engines...Thanks. [ 11. December 2003, 08:02 PM: Message edited by: Nathan P ] Quote Link to comment Share on other sites More sharing options...
Nate1647545505 Posted December 12, 2003 Author Report Share Posted December 12, 2003 annnnnnnnyone ? graemlins/bubbrubb.gif Quote Link to comment Share on other sites More sharing options...
Ziggy1647545504 Posted December 12, 2003 Report Share Posted December 12, 2003 Sounds like you guys have issues. As for the lack of power and the glowing manifolds, when my Caddy did that it was due to a lean misfire. Are you absolutely positive you've got the distributor located properly? You could be like one tooth off. That could be part of it. Do you have a service manual? Go to the trouble shooting section, select a symptom one at a time and go through cross referencing possible causes. If you come up with several symptoms that all seem to indicate one or two things, start there. I don't know that much about the electronics on that truck, does it have an Idle Air Control module? I had to replace mine when I did headgaskets on my car a couple of weeks ago. Another thing that could be happening, that truck is OBD2, there should be I think 2 o2 sensors on the exhaust, one up stream of the cat and one down stream from the cat. Make sure that there aren't any exhaust leaks anywhere near those sensors. Sometimes an exhaust leak can cause the sensor to send incorrect information to the computer which can lean the A/F mixture out. Take this info for what it is worth, you need to know though, that I am not in any way a certified mechanic. Maybe someone else on the board has an idea? Good Luck! Quote Link to comment Share on other sites More sharing options...
Guest nevarmore Posted December 12, 2003 Report Share Posted December 12, 2003 I'd guess the distributor too. In the editorials of the latest Car and Driver (the one with the Ford GT vs. Porsche vs. Lamborghini), an editor talked about his frustration with the smog check. He had done some work on his towing truck (late model GM) and it was throwing a similar code. Because it was throwing codes it was failed at the smog station, despite passsing the tailpipe test. Turn out that the distributor has to be installed spot on with some special tool. The author had installed many smallblock GM distributors in his day, and the truck ran perfectly, but theres something wierd about the newer models that almost require a shop to install it. Quote Link to comment Share on other sites More sharing options...
Dave1647545494 Posted December 12, 2003 Report Share Posted December 12, 2003 my bet is the cams in wrong. the timing is retarded too much thats why it gets so hot. did you degree in the cam? its important on late model motors to degree the cam. even though it looks to be in time on the marks it could be off as much as 15 degrees. you may also need a new computer program to make the truck run right. Quote Link to comment Share on other sites More sharing options...
1TrueSS Posted December 14, 2003 Report Share Posted December 14, 2003 Originally posted by Nathan P: 1998 GMC 2500 with the 5.7 (detuned LS1?) motorIs this a engine swap truck? LS1 based truck motors did not come out till 1999! 4.8 5.3 and the 6.0, no 5.7! The 5.7 was not a LS1 in the 98s! Quote Link to comment Share on other sites More sharing options...
Nate1647545505 Posted December 14, 2003 Author Report Share Posted December 14, 2003 Not that we are aware of. We reseated the timing chain cover with a new pickup plate and new sensor. Whats up with GM's one time use crapola? It is a 350, with the EDI ignition system. My LS1M Scantool reads it accurately and with no problems. Late 98 build? Quote Link to comment Share on other sites More sharing options...
Ziggy1647545504 Posted December 16, 2003 Report Share Posted December 16, 2003 Originally posted by Nathan P: Late 98 build? No. 1999 was the first year for the ls1 motor in the trucks. That was also the first year for the body style like 02Silverado's (see sig). Your buddy's truck does however have the Vortec motor. That Vortec 350 is strong. Quote Link to comment Share on other sites More sharing options...
Nate1647545505 Posted December 19, 2003 Author Report Share Posted December 19, 2003 The cam is installed properly, along with the distributor. We are now leaning on the chip time. We need to modify certain aspects of the computer. We are sure that the cam is causing the lean condition, but i will have more data from logs of the O2s. We just need to know what to modify. If the cam is to extreme, our guess is that we need to adjust spark and timing along with fuel delivery. Any ideas? Thanks! Merry Christmas! Quote Link to comment Share on other sites More sharing options...
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