Intro/Trouble shooting help thread.

[Jakemd98]

Hi every body... I just wanted to introduce myself and ask a few questions.

I recently traded a old jeep i had for my 98 Yukon. I traded with the knowledge that the yukon had a few problems, but they seemed easily fixable and a good deal... well 3 weeks later i am still having issues with it, so i figured i would bring my issues here and see if y'all couldn't help me out.

Here's the issues i have come up with and fixes i have done so far.

Cyl 4 misfire - replaced plugs and the whole distributor

Low compression in cly 4 (result of bad distributor and carbon build up?). Ran sea foam through intake and oil pan, techron in fuel.

sometimes has no power and an intake backfire when trying to accelerate - inspected valve springs, they all looked good.

So what i am dealing with at this point is the yukon will run great one day, and terribly the next. It seems to cycle between a hard misfire at idle with decent power all the way through the rpm. Then it will idle fairly smooth with no power through the rpm and it will backfire through the intake if i keep my foot in it. Then it will run like it should as far as power, but have a rough idle.

Also today a new issue has popped up with the whole electrical system going dead after i turn it off and then when it comes back on (few seconds later) the clock is reset but not radio presets, SES is off, and the motor doesn't want to idle initially (like the batter was unhooked). Only codes i'm getting is an occasional cyl 4 misfire and a rich/lean code on the right side's o2 sensor. Finally the oil is staying clean, no coolant or fuel is in it, and exhaust does not smoke or smell like coolant.

So what does this sound like to you? PCM going bad maybe or just extreme carbon build up?

Thanks for your help!

 

[oldsalt]

When you replaced the dist did you get the timing adjusted? I would start with that for a baseline.

As for the electrical problem...well...I'm not very good with electrical crap. That being said, I would start with cleaning up the battery terminals to get a good contact. I hate the side terminals so I changed mine to top post connectors. Since then I have not had any of the glitches I use to have.

 

[Jakemd98]

yeah... i have a friend who has a scan tool at work, so i borrowed that and got the timing at 0 degrees. I did, however, put the old gear back in rather than use a new gear. The old gear seemed to be pretty worn and i didn't want to chance a new gear damaging the cam gear.

 

[SunlitComet]

if your cam retard is correct and cap, wire , rotor are good then your cylinder may have been washed down from a leaking injector. If you can not find loose or corroded electical connections then you may want to chuck your injection spider for the new improved Supercalifragilisticexpialidocious system. A kit would cost you $230 at amazon. It fits your situation very well since you have no cross leaks and with backfiring. Carbon build up in the cylinder would actually increase pressure. a washing out by excessive fuel would lower it. After running for a while what does the plug look and smell like?

Btw clean your battery terminal and make sure they are good and check for loose or corroded grounding points. Would not touch the pcm or O2sensor at all.

 

[Jakemd98]

plug is black, and has a greasy film on it after running for a bit.

Would the injector issue be a main injection system (the spider) or could i replace the individual injector and be good?

 

[96ProCompTahoe]

replace the whole assembly. replacing one injector may still have it letting more or less fuel than the others if they aren't all matched.

i second the ground and battery cables.

Welcome to the site and good luck with getting her fixed.

 

[Jakemd98]

thanks for the help... guess ill have to save up a bit for the injector system. It will just be nice to finally have this thing running right.

 

[SunlitComet]

Just for thought can you give actual pressure numbers on the cylinders please? There is something I would like to check.

 

[Jakemd98]

i had about 160-170 on cyl 4, and 210 on all the others IIRC.

 

[SunlitComet]

with 160 on #4 210 on others your are very close to the threshold on pressure imbalance so you might still if at all notice a minor lope from your exhuast when running with a new injector but if the scanner doesn't show any misfiring on that cylinder afterwards then you should be good for a long while. Untill something else breaks.