Hi everyone,

Been browsing the myriad of threads regarding this car and the litany of reasons it can cause a misfire.

When I got this car it had numerous codes thrown, lots of work to do but overall it ran very well even with the codes it was throwing. up until this point as a matter of maintenance I've changed all the coils, coolant temp sensor, spark plugs, upstream oxygen sensor(had a broken wire) MAF sensor, Fuel Filter, Air filter, etc. I did the valve cover gaskets as the plug cylinders had quite a bit of oil in them. that has stopped.

This last winter, put it away, put fuel stabilizer etc. is now running like a bag of S*it. throwing general misfire codes. I know you want to see the codes, but I don't have them right now.

Pulled out the NGK plugs today that I put in originally as I've heard these plugs and this car aren't good friends, and replaced with Bosch double iridiums, did a hard reset, checked everywhere for vacuum leaks, still misfiring, although not throwing codes at the moment and definitely running a bit smoother but still has a misfire.

I plan on pulling out the new coils as I did kinda cheap out on those at the time and reinstall the originals to see if any changes are apparent. I'm also going to give the fuel injectors a good cleaning.


So I know there is still a lot to check, like the dipstick tube seal and the TPS, but I was wondering...

-Can old coolant or the wrong specced coolant cause issues? As I know temp variations can cause issues with this car.
-Will last seasons gas cause issues? I only run premium and used stabilizer, still have half a tank to get rid of.
-I tested fuel pressure and is running at consistent 33 PSI, I cant get a consistent answer on the web if that # is right, some say yes, some say no.

Thanks in advance.

 

Fuel pressure should be 45.

 

Put the fuel pressure gauge back on it this morning, is still running at 32-33 psi. fuel pumps are reasonably priced, I'll try that first before the coils, it is definitely running smoother than yesterday but has a subtle lope at idle and a flat spot at launch so I'm hoping to get rid of that.

 

Fill it up with high test, that should give the gas in there a boost. Mine kind of laughs at me until I add new gas after a long sit.

 

Fuel rail pressure is 45 psi without vacuum.
If you get 32-33 psi at idle with vacuum hose connected to the fuel pressure regulator, that is probably correct.
Type of coolant has nothing to do with it.
Old fuel makes things worse. Drive till you have used as much of the fuel as possible, and fill it up with quality fuel, before you throw any parts and money on it.

 

Well pull my lips off.......

On a larf and a spate of boredom, I decided to inspect the IAC, someone had been at it before me as the bolts holding it in had been stripped which of course led to a whole debacle of removing it. I pulled it out and cleaned everything out, reinstalled and did a cold start which had been running quite rough on cold starts up to this point. But smoothed out once warm.

And lo and behold, it seems to have squared away the roughest part of the cold starts, it still has a slight lope at idle but I'll wait and see what a fresh tank of premium will do.

 

IAC idle air control (valve) for the ignorant like me...I have no idea where to find it .

 

IAC is mounted directly on the throttle body.

Fresh tank of fuel did nuttin'

GM LS motors require 52 psi of pressure at the rails if I understand correctly, 33 does seem low to me (we are doing a 5.3 LS swap into a 91 suburban right now as well)

Idle still loping, it's not horrible but bothering me.

However, throttle response and acceleration is the best it's ever been(I've really only done any real maintenance to this thing this year so its to be expected honestly) so all this attention has really cleared up the old girl.

Next step will be to clean up the fuel injectors and if it still doesn't fix it, I'm going to swap the old coils back into it to see what it will do.

might be swapping this one out for a 5.0 supercharged xf..........still pondering on that one.

 

Out of interest, when did you last change your fuel filter ?

 

2 weeks ago.

 

I just was wondering, maybe the little filter bag on the pump is restricting flow.

 

I often use an OBDII reader while I am driving my car set to display fuel pressure, and it is always right around 55 psi. (+ or - 3 psi)

 

Havent been able to work on this much and haven't reached any kind of a conclusion, I'm considering changing out the fuel pump, and cant find an IAC valve to save my life.


I'll just sit here and bang my head off the table for a bit.

 

bosch plugs???? no


http://jagrepair.com/images/Training%20Guides/881%20Manual-9-5-01.pdf