When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
99 5.3 with 150k. Just did stock rebuilt 862 heads with a mild port job by myself (swirl ramps, bowl blend and valve stem smoothing). Straub retrofitted rockers, moly 5/16 pushrods, Morel 5315 lifters, LS2 trays, Cloyes stock replacement timing chain and gears, GMPP HV oil pump. I got some used lower mileage knock sensors from this forum and they looked much better than what I pulled out.
The Top end is a new Dorman truck replacement intake, Stock Ported TB, 1" TB spacer and 72lb @ 58psi bosch fuel injectors.
The engine is Supercharged, centri torqstorm with smallest 3" pulley pushes alot of air at idle, running a small FMIC 26"x7"x4" cheap EMUSA, Dual BOVs, 44mm that opens at 12" and a 38mm that opens at 20" vacuum. Exhaust is transfered over from previous motor which is 1 7/8" SS headers full length, 4" merge into a 3" catback.
Started it up with my tune from before the rebuild which was the same motor besides the Above changes (cam/heads/intake) and it was running 10:1 AFR pig rich. This is because the cam is only pulling 13-15" of vacuum which seems low. It also was only showing 8-13* of timing when I was commanding 19-21* at idle. I had to increase my minimum knock sensor timing to 18* and now its idling with 18.5* timing. Idle RPM wont seem to go lower than 700-750rpms no matter what I have the idle screw set at and ive got it running 14-15:1 AFR at 55-65kpa idle. I haven't gone in to anything else tuning wise. BUt would like some help as to why I can't get it to idle lower than 700-750rpms and where I should be around timing wise. My vacuum seems about 4" too low and I was told by Cam motion this thing should idle around 600rpms and pull more vacuum.
Last edited by customblackbird; 04-06-2017 at 10:59 AM.
99 5.3 with 150k. Just did stock rebuilt 862 heads with a mild port job by myself (swirl ramps, bowl blend and valve stem smoothing). Straub retrofitted rockers, moly 5/16 pushrods, Morel 5315 lifters, LS2 trays, Cloyes stock replacement timing chain and gears, GMPP HV oil pump. I got some used lower mileage knock sensors from this forum and they looked much better than what I pulled out.
The Top end is a new Dorman truck replacement intake, Stock Ported TB, 1" TB spacer and 72lb @ 58psi bosch fuel injectors.
The engine is Supercharged, centri torqstorm with smallest 3" pulley pushes alot of air at idle, running a small FMIC 26"x7"x4" cheap EMUSA, Dual BOVs, 44mm that opens at 12" and a 38mm that opens at 20" vacuum. Exhaust is transfered over from previous motor which is 1 7/8" SS headers full length, 4" merge into a 3" catback.
Started it up with my tune from before the rebuild which was the same motor besides the Above changes (cam/heads/intake) and it was running 10:1 AFR pig rich. This is because the cam is only pulling 13-15" of vacuum which seems low. It also was only showing 8-13* of timing when I was commanding 19-21* at idle. I had to increase my minimum knock sensor timing to 18* and now its idling with 18.5* timing. Idle RPM wont seem to go lower than 700-750rpms no matter what I have the idle screw set at and ive got it running 14-15:1 AFR at 55-65kpa idle. I haven't gone in to anything else tuning wise. BUt would like some help as to why I can't get it to idle lower than 700-750rpms and where I should be around timing wise. My vacuum seems about 4" too low and I was told by Cam motion this thing should idle around 600rpms and pull more vacuum.
It takes air to increase RPMs. What are the IAC counts? Find out where the air is getting in besides the IAC if closing the blade doesn't bring the RPM down. And the TB set screw is nor a idle set screw. It is there to prevent the blade from sticking in the bore when closed. It can be used to shift the IAC counts up or down to an extent but it should not be used to set an idle speed. And the statement I bolded should not be used for what the timing at idle is. And it would be more helpful to state manifold vacuum/boost in kPa units not " of vacuum.
It takes air to increase RPMs. What are the IAC counts? Find out where the air is getting in besides the IAC if closing the blade doesn't bring the RPM down. And the TB set screw is nor a idle set screw. It is there to prevent the blade from sticking in the bore when closed. It can be used to shift the IAC counts up or down to an extent but it should not be used to set an idle speed. And the statement I bolded should not be used for what the timing at idle is. And it would be more helpful to state manifold vacuum/boost in kPa units not " of vacuum.
I agree. IAC counts are at 0 when at idle. No matter the TB blade postion. I did test the IAC by removing and pluggin it in and it moved all the way out. WHen I first start it the IAC counts are higher and then go down to zero. I have a new cheap IAC as a spare that I tested and have the same thing.
I understand the timing was not correct but I had to get the timing up in idle. it was yanking to the minimum timing of 8* for some reason. I wasn't gettng any Knock or retarded timing through HPT Scanner. I'm only assuming that the cam is making the PCM think there is knock when there isn't so I would have to dissable the Knock sensors or edit something to fix that. I'm looking at the "idle airflow vs coolant temp vs Gear", idle startup airflow initial ECT. I Dont believe I'm getting any leaks as its all really new and tight. I just think its weird that I can't drop the idle to 600-650 on command.
The intake is brand new, all gaskets are brand new. No idea how or where the air is getting in. I couldnt find any leaks. But I think the Supercharger is forcing air into the motor even at idle bc when I removed the 44mm BOV (closest to the supercharger) air is shooting out of the opening.
When I checked my idle vacuum is in the 55-65kpa range. With the stock cam and motor I was around 35kpa.
From what I have been reading there are air tables I need to modify in the idle are now all off.
Last edited by customblackbird; 04-06-2017 at 02:20 PM.
So I've been going through things trying to see if there are any obvious leaks. I changed some things around that could be issues.
I then hen did some reading and heard that the ported TBs can cause issues if they get too carried away with porting around the blade area. So I snapped these pics to show an u touched TB to the ported one (I didn't port it) the TB blade holes are the same size. The ported TB clearly has more room around the blade. I was thinking of plugging the TB hole to limit air flow.
I have solved the idle surging/hunting. I had to go in and increase the base airflow tables 2-4g/sec. So now its idling steady around 700rpms (+-50rpms). I pulled the dorman intake and swapped on a new GM Delphi stock intake with new gaskets and retorqued. I checked everything off the intake vacuum wise and have NO leaks! I put it all back together and I have the IAC in the 74 range but not fully warmed up. It was in the 50-60 count range before the intake swap. But it wasn't fully warm (131*F) and it was still only at 74 counts. So I think thats working good now. I still have shitty vacuum at 13.2-14" at idle. Here are my thoughts and Any help would be great! I have the next few days off and I would love to get it working as I have time to work on it.
1.) This motor is supercharged, torqstorm centri with smallest 3" pulley. I pushes ALOT of air low in the RPM Band (even idle). With the BOV barely open (due to the lower vacuum) I have a TON of air coming out. My only thought is that the air being forced out of the supercharger into the TB/IAC is soo much even at idle that this thing is lowering vacuum as its replacing it with positive air. This leads me to my next point.
2.) My all STOCK 5.3 had 150k, it is the same motor minus the heads/cam and has the same blower and pulley... no other changes. It only pulled 19" of vacuum at 550rpm idle... thats 3.5" lower than the vacuum these normally pull at 22.5" at idle. My only assumption is that the supercharger is displacing vacuum with positive air being forced in through the IAC/TB. MAP readings are steady around 58kpa at 131*F during warmup.
3.) Pushrod length. Heads are milled .005 (supposedly from ebay reman company) combined with MLS head gaskets I was told to run stock length 7.4" pushrods. I put in 7.4" Moly and combined with the morel 5315s I should be fine (cam motion said its stock base circle cam). I pulled the driver valve cover and checked rockers and they are all tight. Valve train is quieter with the straub busings over stock. but I can mostly just hear the supercharger whine out of the filter. If the pushrods were too long I would be getting fluctuating MAP readings and they are pretty steady.
4.) Cam being 1 tooth off. I thought I might have screwed up the cam install and got it a tooth off. I verified pics of the install and the dot looks pretty lined up and I remember checking it thoroughly. Cam was installed straight up, just dropped it in and lined up the dots (3 bolt cam). I'm going to post a pic of the cam dots so its seen. The bottom dot is alittle harder to see but it was lined up. I had to rotate the flexplate a smidge to get the flexplate stop bolted down and the teeth to interlock so thats why the dots shifted a smidge... but its clear they are lined up perfectly.
I'm going to upload my Log so you can see in HPT what its doing. But I'm not sure about timing on this thing. I have it at 24* at idle (i was around 21* stock cam). Due dual pattern higher lift and mild duration's like more or less timing at idle? I thought it was more due to them being less efficient, but they will require less timing at WOT?
Last edited by customblackbird; 04-10-2017 at 09:31 AM.
04-06-2017, 10:53 AM
214/228 custom cam tuning 
