Cannot set timing

[Tcapper28]

Hi everybody, I'm new to the site and I'm having a problem setting the timing on my 1994 GMC Sierra SLE 5.7L TBI. I've had the truck for about 3 years and when I got it it seemed to be low on power. I changed the plugs, cap, rotor, and wires. 3 of the plugs were fouled really bad. Truck ran perfectly until a few months ago when it started to misfire when I thought it was changing to OD, if knocked it down a gear it seem to run fine, but the problem has gotten consistently worse. The tranny has checked out ok. Also since the day I got it the check engine light would come on after a minute at idle and clear when driving. To get to the problem, when I went to set the timing, the timing mark is erratic and I cannot get it set to a baseline of 0 degrees. The timing chain is ok, so I've ordered a new ignition module, coil, and IAC valve on spec but they haven't arrived yet. I know there is a misfire, but I'm looking for any ideas on where else to look. If this has been answered in another forum I apologize. Any help would be greatly appreciated. Thanks.

 

[smdk2500]

When your setting it you are unplugging the tan/black wire before checking correct?

 

[PlayingWithTBI]

I know there is a misfire, but I'm looking for any ideas on where else to look. If this has been answered in another forum I apologize.

What's your fuel pressure at idle and under load. Those misfires could be lean pops.

 

[Tcapper28]

Yes the timing plug is disconnected and I haven't put my fuel pressure tester on the system yet, but with that said there appears to a lot of fuel at the TBI. I'll check that when my other parts arrive. On that note, on the highway when put under a load at lower RPM's like when changing to OD is when it shudders, pushing it to passing gear there is/was ample power. But again one of my buddies is a tranny guy and he gave the tranny a once over and that appears to be ok. Just looking for some ideas or somebody that has encountered this problem. Thanks.

 

[Schurkey]

Hesitation on my truck was worse as the engine was warming-up. Not fully cold, not fully warm. Adding a couple pounds of fuel pressure cleared it up.

I would be connecting a scan tool, looking at short- and long-term fuel trims; coolant temp sensor, MAP sensor, and O2 sensor. (But look at data from ALL the sensors while you're in there...)

If the O2 sensor has more than 50K miles, or 5 years, it's time to replace it unless you can PROVE with the scan tool that it reacts appropriately. A MIL at idle is "probably" a faulty O2 sensor; but it could be something else; which you'd find out when you connect the scan tool.

Coil and IAC are unlikely to help. Maybe the module. I'd have TESTED those parts rather than just ordering new ones. Given the crappy quality of Chinese junk parts, what's in the truck now may be better than the stuff you just ordered.

 

[Tcapper28]

Hey thanks for the reply, I don't think that the IAC valve would cause this particular problem but upon checking further it is a little gummed up and I found that the EGR valve is also shot. As far as ordering the parts, I agree with you on the chinese parts. I'm sticking with A/C Delco whenever possible. Given the age of the old girl and besides the cap, rotor, plugs, and wires, I believe everything is original to the truck, so I have no problem replacing the parts that I've mentioned, just so everything is new. I'm not breaking the bank so throwing a few bucks at it isn't a problem. The one thing I didn't think of was the O2 sensor. That'll be the next check, thanks for the input.

 

[Schurkey]

Are you thinking that AC-Delco does not sell Chinese junk? In fact, it's a high percentage of their product line.

 

[Tcapper28]

I am well aware of what is chinese and what is not, so I am trying to put what I can that's closest to domestic that I can. I have ordered hundreds of parts for my vehicles over the years and try to use parts that I've had the best luck with. Tell me what's solely domestic and maybe I'll buy that. My original question was about my truck, not to get in a pissing match with somebody that hates the chinese. I'm on several chat sites for the several vehicles I have and joined this site because I had a specific question about my truck, not what parts are available. So, thank you for your input.