: 99 STS, almost working



tresero
02-02-08, 05:53 PM
My 99 (absolute POS as far as I am concerned), has 102K miles. It has been missing at idle, but no stall, hesitates through 3 - 4k rpm on medium acceleration and stumbles out of idle and up to about 1500 rpm.

Did all the usual stuff, replaced EGR (I know I could have cleaned it, but it is old), cleaned the TB, tightened battery, checked for vacuum leaks.
No change and no codes.

Before I tightened the battery it would throw lots of 'em, it has been a month and those are gone so that fixed stuff like the U1255. I got a U1040 today along with the typical C1783 and C1785, but they went away in about a second.

I have had intermittent P0171 and P0174, but they seem to have gone away for the last week or so.

I am stumped. I didn't really think cleaning the TB would matter but it was easy and cheap, same with the EGR (well not cheap, but easy).
This car has been possessed since my father bought it new and was given a free extended warranty because he was going to return it.

Sorry to rag, but my 98 Explorer has 200,000 miles and runs better than this GM monstrosity. I know what I won't buy again, but I hope to at least fix this nagging problem. The STS reminds me of a Jenson-Healy I owned way back when, awesome when it runs, but lord help you when it doesn't:mad:

JimD
02-02-08, 06:30 PM
....It has been missing at idle, but no stall, hesitates through 3 - 4k rpm on medium acceleration and stumbles out of idle and up to about 1500 rpm.Spritz water on the plug wires in a dark location; look for arcing. Check for corrsosion at the coil tower high voltage terminals. Plugs have how many miles??

.... checked for vacuum leaks.....I have had intermittent P0171 and P0174, but they seem to have gone away for the last week or so.You could have fixed the P0171/0174 by touching the vacuum hoses. Those two codes together usually mean there is air entering the intake somewhere other than through the throttle valve.

Sorry to rag, but my 98 Explorer has 200,000 miles and runs better than this GM monstrosity.Ford is capable of building their own brand of monstrosities.

Ranger
02-02-08, 06:33 PM
Your problem sounds alot like you are in need of wires and/or plugs. Are they original? If so, I'd replace then and stick with OEM replacements.

Your P0171 & P0174 is a vacuum leak somewhere.

tresero
02-02-08, 06:46 PM
The plugs and wires were changed, but not OEM. I will buy originals. Is the dealer the only place to get them? I also suspected wires, but figured a misfire in the ignition system would throw a code.

I can't see a vacuum leak, but I did find what I thought was a pcv valve (don't think it is) popped out. This is the side next to the firewall, I think the pcv is on the radiator side valve cover.

JimD
02-02-08, 06:58 PM
The plugs and wires were changed, but not OEM. I will buy originals. Is the dealer the only place to get them?Lots of places stock ACDelco plugs and wires or you can buy them online.
I also suspected wires, but figured a misfire in the ignition system would throw a code.Not always; the misfire has to reach a certain level before a code is set. This avoids nuisance codes.
I can't see a vacuum leak,...You would be more likely to hear a vacuum leak.
.... but I did find what I thought was a pcv valve (don't think it is) popped out. This is the side next to the firewall, I think the pcv is on the radiator side valve cover.The PCV valve is on the firewall bank of cylinders. If the valve was still connected to the vacuum hose, that was not the source of your vacuum leak. I would double check all the rubber hoses you can find under the beauty cover.

Ranger
02-02-08, 07:17 PM
The plugs and wires were changed, but not OEM. I will buy originals. Is the dealer the only place to get them?
NO. Try http://www.rockauto.com. Much cheaper than dealer prices.

tresero
02-02-08, 09:01 PM
Still hurts, These wires are not OEM, but I don't remember changing them. The plugs were probably changed at the same time.
I hate to throw money at the problem, is there a reliable way to check if the wires have a problem? And why are they so much money?

The plugs are no problem at $5 each, but $108 for wires (184 at the dealer) I don't want to just spend the money since the wires are probably not that old.

Ranger
02-02-08, 09:12 PM
Not sure why they are so expensive, but replacing them solved a similar problem on my '97. You could try misting them in the dark and look for arcing. You can also measure the resistence with a DVM. Someone els will have to tell you what to look for there though.

tresero
02-02-08, 09:31 PM
Well I just misted them with water and saw nothing on the front side (back can't be seen), but of course that doesn't mean much. I guess I will change the plugs and measure the wire resistance tomorrow. If one is off I will know.

Ranger
02-02-08, 09:55 PM
Keep in mind that the resistence will varry by length, That much I do know. Now, that said, I do recall measuring mine. Saw no great discrepencies. Changed them anyway and the problem went away. See if any of this sounds familiar.
http://www.cadillacforums.com/forums/northstar-performance-technical-discussion/25119-stutter-engine-trans.html

zonie77
02-02-08, 10:09 PM
Measuring resistance usually won't tell you if the insulation is breaking down. Putting it on a scope would be much better but scopes aren't as available as they used to be.

digitalcaddie
05-13-08, 03:09 PM
I read somewhere that the resistance of the plug wires should be in the 1k-12k ohm range depending on length. If the resistance is greater than 15k ohm, replace them. I replaced mine a while ago and the resistance of the new ones were all below 10k ohm.

Submariner409
05-13-08, 06:10 PM
This is sounding more like the problem of two or four plug wires going to the wrong plugs from one or two coil towers.

Your engine uses a waste spark system: 4 coils are used to fire 8 plugs. BUT, the coil phase is critical, so each wire has a specific plug/tower relationship. Per coil, one plug fires near TDC of the cylinder which is on the compression stroke, while another plug fires simultaneously in the cylinder which is 180 degrees from the first (exhaust TDC). OEM coils are marked with cylinder numbers: if that has been upset, you need a good factory diagram to get it right again.

This may or may not be your problem, but it's worth a try. (N*'s don't like anything but ACDelco plugs and wires. Your plugs are 41-950, I believe.)