98 Vortec woes K2500 RCLB running like crap

[3500GMC]

Member 1GMCfan's truck. 98 K2500 5.7 Vortec. Many new parts. 150k miles. The list as follows IIRC.. There might be a few parts that he replaced that I missed..

Cap, rotor, wires, plugs, spider injector assembly & FPR, coil, CTS.

He did a short video from an Iphone which captures it's popping and backfiring fits while going down the road. Not a happy vortec, ... or owner for that matter..

[video=youtube;DuhRar_sBkI]http://www.youtube.com/watch?v=DuhRar_sBkI&feature=youtu.be[/video]

 

[ak diesel driver]

almost sounds like a burnt valve but not quite

 

[3500GMC]

almost sounds like a burnt valve but not quite

Ya I know.. Like even a wiped lobe but this thing's a roller engine (based on what it SHOULD be) so it'd be in REAL bad shape by now if a wiped lobe was in fact the deal.

Tying to get a plan of attack.

Probaby start with the basics, compression check....

 

[ak diesel driver]

I wonder if a lifter is sticking in the pumped up position???????

 

[btfarm]

Pole piece on the distributor could have a chunk of insulation flaked off and it's shorting to ground or another pole.
I've seen that on HEIs before.

 

[6.2 turbo]

I assume the dist gear was checked and the timing set to 0 degrees. I would check,or change the dist cap again. Does it start ok ?

 

[3500GMC]

To my knowledge the distributor hasn't been touched except for the cap and rotor.

And it actually starts and idles real good. No chugging, smoking nothing..

 

[THEFERMANATOR]

Start with the obvious first, and do a compression check. O2 sensors can wreak havoc with how those engines run, as well as knock sensors. Could also be a fluttering EGR valve causing it. The spider injection is the most common problem point on them. Could also be a worn distributor gear, but I would almost expect that to throw a TDC offset error code.

 

[someotherguy]

btfarm - being a Vortec there's no magnetic pickup coil in the distributor like the TBI units, and yeah those are somewhat known for going bad. The Vortec setup though just has a reluctor type wheel and the cam sensor, hall-effect style setup, and the cam sensors rarely go bad.

6.2 turbo - excellent advice on the distributor gear as the Vortecs are known for having a batch of improperly heat treated gears that went horribly bad, way prematurely. Apple core wear is the common failure and they will run like crap.

You don't just set the timing to zero with a timing light on a Vortec though, unfortunately. They had to go and make it a pain. There's no bypass wire to disconnect like on a TBI setup.

Best thing to do is not attempt adjusting the distributor unless you have a scan tool on hand that can read the "cam retard" figure, and usually it takes a somewhat high end scanner, though several of the lower end Auto Xray units are capable. If pulling the distributor, make TWO marks - the distributor body position AND the rotor position. When reinstalling, attempt to get it as close as humanly possible to those same two marks. That should allow it to run well enough to fine-tune with the scanner. Then use the scanner and adjust the distributor until you get the cam retard number to within +/- 2 degrees from zero - while holding RPM's to at least 1,000 to ensure a good reading. You cannot do this based on the reading at idle or below 1,000.

Now while I believe the distributor gear is high on the suspect list, you should also check the distributor itself for wear in the top bushing. Grasp the rotor and try moving it from side to side. If it doesn't move, gently twist it either direction to see if it turns, then try the side to side movement again. If you can get any real noticeable movement...time for a new distributor.

While we're at it, I know the FPR and spider have been replaced (hopefully took the opportunity to ditch the poppet valve setup and go for the MFI conversion with the individual injectors) - but what's the fuel pressure looking like? If it's not 58~62 psi then you still have a fuel delivery issue. Vortec small blocks do not like it at all when fuel pressure falls anywhere short of spec, especially with the poppet style injector setup, it really requires fuel pressure be up to spec to force those valves open.

Richard

 

[3500GMC]

Yep high end scanner, distributor adjustment (timing), little old vortec is happy. Something to the tune of 14* retarded!! Yeaaa.. that'll choke off 'bout any engine..

I Woulda posted back earlier, but didn't realize the owner (1gmcfan) was anti-social.. :hello:

Thanks to all replies.