Oct 2014
Gain extra benefits by becoming a Supporting Member Click here find out how!
Silver
Gold ***Platinum***
andylee32Boosted54 DOC396 (9)blue56 (12)pistol (13)
Gremlin (3)bobyone4dad (2)PLS (3)55sedanman50Ragtop (6)
MoboMac (3)jrogers885 (3)MrImpalaMan rddaves54 (7)
alexm900 (3)TMURF (8)fightclub 40 Ford (3)my60belair
Wideking Fhunter1 (9)GreatNorthWoods fosterdl (2)
twilliams3 (13)
longboard (6) jel1957 (6)
Rick Dorion (2)Red64SS (4)
khardy (14) idaho (6)
ed72073 (5)
Bowtie Crazy (5)
nauta (9)
cyclops (3)
fonc (2) 57belairman (12)
55sd-delivery (11)
Classic Performance Products Classic Parts
Ciadella Interiors American Auto Wire Art Morrison.com
Exile® Battery Keeper™ 6/12 volt charger w/ LED battery monitor
Low priced Genuine GM Auto PartsEcklers AutoMotive
Hellwig Products IncPerformance Rod & CustomClassic Industries
Impala Bob's Bob's Chevy Trucks Bob's Chevelle Parts Bob's Classic Chevy
 

Recent Hot Topics
Current Quote
"Looking forward to ploughing thru the wealth of information the site has to offer."
~ New Member
Recent Topics
LMC Truck Join the Community today Join Us Now ďż˝



Username Post: Timing issue on 5.7L TBI        (Topic#256152)
blackZ71Jeff 
Contributor
Posts: 163
blackZ71Jeff
Reg: 10-05-10
01-19-11 09:34 AM - Post#2034195    

Im sure Cheyenne or most others have gotten tired of reading about the woes with my truck but here is my question.

After replacing plugs, wires, cap, rotor, camshaft position sensor, and MAF sensor truck was running great, despite the wire tie and gorilla glue I had to put on distributor from the front screw mount cracking. Damn plastic distributor!

I went to make sure the distributor cap was still tight after about 2 weeks and the distributor turned. Since then I am experiencing misfires and backfires, bad gas mileage and doesnt seem to have all of its get-up-and-go.

Do I have to disconnect the timing set wire to manually turn distributor to find my sweet spot? I understand the ECM will constantly readjust timing if not disconnected. Is it best to disconnect, find the semi-correct position of the distributor and then tighten down and reconnect set wire?

Is there a way to set timing without scan tool? Can I do it with light? Distributor was never removed, cam sensor only goes in with rotor turned so gate will allow it to be installed so I have done nothing to disrupt the distributor. Truck will spin the tires with the power so I know the timing is not that far off. Idles fine until warm and then fluctuates about 1-300 rpm.

Im at a loss because I understood that the OBD2 scan tool is needed to set the ECM timing, but if the timing set connector is unplugged the timing can be set without scan tool. Which is correct, or are they both able to be done? Do I need to disconect ECM power to reset the retarded timing code so it wont re-adjust timing once set with timing set connector disconnected?
Do not follow where the path may lead, go instead where there is no path and blaze a trail!


Edited by blackZ71Jeff on 01-19-11 09:37 AM. Reason for edit: No reason given.

 
Low priced Genuine GM Auto Parts
355Cheyenne 
Senior Member
Posts: 3765
355Cheyenne
Loc: Northern MN
Reg: 10-27-04
01-19-11 09:58 AM - Post#2034215    
    In response to blackZ71Jeff

I am confused now. I read MAF Cam position sensor OBD2 and TBI. This cannot be TBI, this must be CSFI 96+ and there is no "setting base timing" but rather timing offset. Timing is controlled via a reading from the crank sensor and is in no way adjustable with out custom tuning. What can happen is if the distributor isn't indexed correctly you can get crossfire, this is where a spark is called and it jumps to the wrong pin in the cap because the wrong pin was closer then the correct pin. Instructions on setting the timing 96+ vortec is in the FAQ. Unfortunately this becomes a scan tool with GM expanded functions required to properly dial in.
98 Silverado k1500 4x4 350


 
blackZ71Jeff 
Contributor
Posts: 163
blackZ71Jeff
Reg: 10-05-10
01-19-11 10:18 AM - Post#2034231    
    In response to 355Cheyenne

That is correct, a 98 K1500 Silverado with 5.7 TBI. OBD2 is the scan tool I have been using to find fault codes. Just talked to my mechanic and said timing can be done both ways. If using light, the set timing connector is disconnected and reset once correct timing is set @ 4 degrees after TDC. No need to repower ECM. I have read the timing instructions by searching and my issue is that it isnt a breakdown of any engine part or removal of distributor. I only replaced Camshaft position sensor in distributor. I didnt quite understand your comment about the MAF?
Do not follow where the path may lead, go instead where there is no path and blaze a trail!


 
someotherguy 
Moderator
Posts: 25980
someotherguy
Age: 44
Loc: Texas
Reg: 08-01-03
01-19-11 11:43 AM - Post#2034258    
    In response to blackZ71Jeff

TBI engines (in the U.S. market) are 1987-1995 and are OBD-I. 1996-up are Vortec, which is the CSFI type setup that he mentioned. 1996-up are also OBD-II. It has a throttle body, yes, as pretty much any typical fuel injected engine would, but it is not referred to as a TBI engine. That's GM's name for the 1987-1995 style setup. Yours is referred to as Vortec.

Unless it was built for the Mexico market, which doesn't have the same emissions laws we have - they ran TBI up to at least 1998 that I've seen proof of! Down here in South Texas you see them every once in a great while; they're real oddballs.

Richard
94 C2500LD / 97 Suburban LS1 / 06 300C SRT8
Check out my truck shop projects


 
someotherguy 
Moderator
Posts: 25980
someotherguy
Age: 44
Loc: Texas
Reg: 08-01-03
01-19-11 11:46 AM - Post#2034262    
    In response to someotherguy

Back to your original post, you can set timing without a scan tool, but it still takes tools and skill. The alternative to a scan tool is a logic probe, and I don't have the first hint as to how the logic probe would be used in this application.

To get it right, and KNOW it's right, you need a scan tool that can read the cam retard angle.

There is no timing wire on the Vortec setup; that's only on the TBI engines.

OBD-II settings/codes cannot be cleared by disconnecting the battery. A scan tool must also be used for this.

Richard
94 C2500LD / 97 Suburban LS1 / 06 300C SRT8
Check out my truck shop projects


 
355Cheyenne 
Senior Member
Posts: 3765
355Cheyenne
Loc: Northern MN
Reg: 10-27-04
01-19-11 01:16 PM - Post#2034287    
    In response to blackZ71Jeff

  • blackZ71Jeff Said:
That is correct, a 98 K1500 Silverado with 5.7 TBI. OBD2 is the scan tool I have been using to find fault codes. Just talked to my mechanic and said timing can be done both ways. If using light, the set timing connector is disconnected and reset once correct timing is set @ 4 degrees after TDC. No need to repower ECM. I have read the timing instructions by searching and my issue is that it isnt a breakdown of any engine part or removal of distributor. I only replaced Camshaft position sensor in distributor. I didnt quite understand your comment about the MAF?




I brought up the MAF because you brought it up in your first post and I was making a point that this isn't a 88-95 TBI because they didn't have a MAF.

You cannot set timing on your truck using a timing light. You can try to confirm timing is relatively close by getting to TDC and looking to see how close the rotor is pointing to the #8 in the plastic housing of the distributor, other than that you need a OBD-II scan tool with the GM extensions to read the CMP offset. Alas there is no way to "time" these engines in the sense you are thinking, but only to set the distributor position to prevent crossfire.
98 Silverado k1500 4x4 350


 
blackZ71Jeff 
Contributor
Posts: 163
blackZ71Jeff
Reg: 10-05-10
01-19-11 06:56 PM - Post#2034439    
    In response to 355Cheyenne

Wow guys...I guess I have an "oddball"! It is the original engine for this truck, a 1998 Chevy Silverado K1500 with the Z71 package and a 350 (5.7L Vortec) WITHOUT a fuel injected intake. Maybe I am using the incorrect terminology for it but I can remove my intake housing and look straight into carburetor. This, to me, is not a fuel injection system but what I refer to be a Throttle Body Intake (TBI). If there is another term for this type of intake I am just an amateur and don’t know how to describe it. I only know of these 2 descriptions.

To Cheyenne, the MAF sensor is between canister air filter and TBI, which I replaced because of the emission faults that showed on OBDII...at the same time replacing camshaft position sensor because of the fault code. I also isolated and located a faulty O2 sensor using process of elimination, due to the fact of the OBII showing me what bank location to work with.

My mechanic (whether right or wrong) explained it to me like this, keep in mind I have not had a chance this afternoon to verify what he described. I had an unexpected visit to ER and haven’t gotten a chance to get into engine to verify:

1: Engine does not need OBDII scan tool to set timing as it does have a timing plate on the harmonic balancer, however the scan tool will erase fault code and cease its attempt to adjust any retarded timing. BTW, it is correct @ 4 degrees after TDC.

2: The timing set connector needs to be disconnected while using timing light procedure and reconnected after timing is set to original specs. **note** The ECM can be bypassed using this method; however the ECM will not erase code without scan tool. By manually setting timing to the CORRECT degree w/o disconnecting will cause the ECM to remain trying to correct any retardation due to the fault code.
So, yes the proper way should be done with scan tool simply for the fact of erasing the fault code which will cause the ECM to react.
Do not follow where the path may lead, go instead where there is no path and blaze a trail!


Edited by blackZ71Jeff on 01-19-11 07:01 PM. Reason for edit: No reason given.

 
355Cheyenne 
Senior Member
Posts: 3765
355Cheyenne
Loc: Northern MN
Reg: 10-27-04
01-19-11 07:28 PM - Post#2034463    
    In response to blackZ71Jeff

The method supplied with the disconnecting the wire is correct chevy p/u 88 to 95 with TBI fuel injection as seen here (first is the injector throttle body, or TBI)


(second is of the engine bay)




What you have is what I have, a Vortec CSFI with a throttle body as all modern engines have but the injector body is in the split intake as a spider assembly with poppet valves over the conventional injector.

(first picture is the torn down intake)


(picture of intake and throttle body)


(second is the engine bay and clear difference, not the "Vortec" on the air box above the throttle body)


That being said, 96 to 98~99 SBC engines cannot be "timed" in the sense that you turn the distributor and set your advance/retard degrees. Turning the distributor does nothing other then change the position of the roter to the points in the cap. The timing is produced inside the ECU by listening to the crank sensor pulses.

The only thing that can be adjusted is the "cam position offset" which requires a specific function set scanner that can read CMP offset. This needs to be set to 0 +-2 degrees which serves no other purpose other than to prevent crossfire and will not affect engine timing. Again, I refer you to the FAQ on these instructions. Talking pure factory 88to 95 is one style induction with a firm set of rules while the 96 to 99 is another form of induction and control systems with another set of rules. Anything in between is not factory or stock and would need to be identified in order to find a solution.

Link to FAQ on timing a 96+ vortec
98 Silverado k1500 4x4 350


 
Low priced Genuine GM Auto Parts
Icon Legend Permissions Topic Options
Report Post

Quote Post

Quick Reply

Print Topic

Email Topic

24542 Views
FusionBB
FusionBB™ Version 2.1
©2003-2006 InteractivePHP, Inc.
Execution time: 0.094 seconds.   Total Queries: 15   Zlib Compression is on.
All times are (GMT -0800) Pacific. Current time is 01:10 AM
Top