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'96 SAAB NG900 SE (R.I.P.), '99 SAAB 9-3
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Discussion Starter #1
My poor NG900 keeps having issues, this time it's hesitation at high boost 0.8~0.9 according to APC gauge.
Previously i attributed this to my modded fuel pump (from a Golf II GTI) blowing hoses inside the fuel tank and dropping fuel pressure but this time when i checked everything was fine.
Also this time it feels like something different. Previously when i had low fuel pressure the car would hop during high boost but this time it hesitates and just starts shuddering(?).
It's hard to accurately describe the feel and sound, normally it goes BWAAAAAA but now it goes BWAAARRRR... , the RRRR part being where it starts hesitating. (feel free to laugh but i can't think of a better way to describe it without taking video/audio) :confused:
The APC gauge still goes to the red as it should because i've set the turbo pressure to 1.25bar, no overboost.
No oil smoke or smell, no blowby, no CE errors, no SID dings. Also i have my doubts that it's a misfire, because my dad's Mercedes had a misfire for a while so i know how that feels and sounds.
Other thing i noticed is that my DIC doesn't do the 5 second spark plug burn off anymore.
And lastly i checked all the spark plugs (all were ok), cleaned them and set the spark gap to 1.0mm with a feeler gauge, this didn't help.

What should i check now? I would like to get it fixed before i do the king cobra pipe (55560602) upgrade.

Ps: i still have the worn ignition switch but i have installed an auxiliary switch to bypass the bad contacts.
 

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I would be thinking of swapping the DIC with your spare to see what happens. We've seen DIC's do this before. Do those plugs you gapped have less that 10K miles? If not, I'd swap them just to be sure and gap down to .9mm.
 

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'96 SAAB NG900 SE (R.I.P.), '99 SAAB 9-3
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Discussion Starter #3
I would be thinking of swapping the DIC with your spare to see what happens. We've seen DIC's do this before. Do those plugs you gapped have less that 10K miles? If not, I'd swap them just to be sure and gap down to .9mm.
I wish i had a spare. Oh man this NG900 is turning into a money pit fast.
I've done just over 16k km on these plugs, which is right around 10k miles.
 

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'96 SAAB NG900 SE (R.I.P.), '99 SAAB 9-3
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Discussion Starter #4
I went out and took a video of the issue but not a single video player on my PC wants to play the video and my loud exhaust is overpowering the mic so there's that i guess.
 

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Try plugs first if you want to keep the money short. NGK BCPR7ES are only $2.50 USD... can't be much for four. DIC is obviously a lot more unless you have a friend near by who will swap for a test.
 

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'96 SAAB NG900 SE (R.I.P.), '99 SAAB 9-3
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Discussion Starter #6
Try plugs first if you want to keep the money short. NGK BCPR7ES are only $2.50 USD... can't be much for four. DIC is obviously a lot more unless you have a friend near by who will swap for a test.
I'll get some plugs then, the car still runs fine unless i give it some beans so i can still daily it.
From what i've read a dying DIC throws misfire codes, so i guess there's still hope.
If the DIC is failing then i can keep driving until it starts giving me misfire codes, then i'll know for sure.
I'll also try getting to the ignition switch to fix it, I should still have my old one somewhere.
The old one had good contacts but got ruined when the spring thingy for the start broke inside the ignition key barrel.

Also unlike other failing DIC's that i've read about my car starts fine, although sometimes when i start and give it gas it misfires at low revs but comes good as soon as my alternator starts charging the battery.
The alternator control wire broke so i have to rev to 2.5-ish k rpm so that it starts charging the battery, voltage is good, last i checked it was 14.3V if i remember right.
 

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Low voltage isn't good for a DIC from what I've seen. At the least, the car runs funny as you've observed.

I've seen a variety of failure modes for DIC's. Sometimes they start with codes and you know they need help. Sometimes they run rough then fail with no codes. Makes no sense to me, but I've seen it reported multiple times. Sometimes they error only under heavy load like yours and still don't throw any codes.

That's not to suggest it's a clear cut DIC issue. But it's possible. The nasty part is that you can't really test them except by substitution... even the WIS uses that method. Saab had a "test tool" back in the day - it was a DIC that had no screw holes in it and was painted a different color.
 

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'96 SAAB NG900 SE (R.I.P.), '99 SAAB 9-3
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Discussion Starter #8
Just noticed another thing. Right after the 5 second plug burnoff the IAC valve would clunk but it doesn't even do that anymore.
 

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Just noticed another thing. Right after the 5 second plug burnoff the IAC valve would clunk but it doesn't even do that anymore.
IAC probably doesn't matter at speed but it would be a good idea to clean and lube it anyway. I don't know about the lack of burnoff. The ECU does that. There is a known issue where the MOSFET transisitors go bad in the ECU but I don't recall the symptoms. You could google old posts here for MOSFET and probably find some posts.
 

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'96 SAAB NG900 SE (R.I.P.), '99 SAAB 9-3
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Discussion Starter #10
IAC probably doesn't matter at speed but it would be a good idea to clean and lube it anyway. I don't know about the lack of burnoff. The ECU does that. There is a known issue where the MOSFET transisitors go bad in the ECU but I don't recall the symptoms. You could google old posts here for MOSFET and probably find some posts.
I've already had a MOSFET for the O2 preheat burn out, which i replaced. I think i made a thread about it.
Also i believe that most of my problems started when my ignition switch started arcing quite badly and even caused a "short to ground" error on the ABS.
ABS fault has been cleared a while ago, no blown fuses.
 

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Has the ignition switch been replaced?If it's funky, perhaps it doesn't do a clean power off and the ECU gets conflicting power signals when the car is shut off... and the burn-off gets bypassed in that? Still, I don't see how that would result in a boost-at-speed issue. A bad ignition would likely give random run-time issues.
 

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'96 SAAB NG900 SE (R.I.P.), '99 SAAB 9-3
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Discussion Starter #12
Has the ignition switch been replaced?If it's funky, perhaps it doesn't do a clean power off and the ECU gets conflicting power signals when the car is shut off... and the burn-off gets bypassed in that? Still, I don't see how that would result in a boost-at-speed issue. A bad ignition would likely give random run-time issues.
I've added an external switch to bypass the bad contacts on the ignition switch.
 

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Don't rule out voltage issues to the DI. T5 and T7 adapt to voltage difference (batt_kor) but I jumped my 9-5 the other day and it missed like crazy under full boost until I changed the battery.
 

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'96 SAAB NG900 SE (R.I.P.), '99 SAAB 9-3
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Discussion Starter #14
Don't rule out voltage issues to the DI. T5 and T7 adapt to voltage difference (batt_kor) but I jumped my 9-5 the other day and it missed like crazy under full boost until I changed the battery.
My battery is brand spanking new, just over half a year of use.
 

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'96 SAAB NG900 SE (R.I.P.), '99 SAAB 9-3
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Discussion Starter #17 (Edited)
Things took a turn for the worse today. At first everything seemed as usual but as i left the city traffic i could barely get any speed on the highway.
This time my engine started hating life just before the APC gauge touched the yellow.
About 60km later i noticed that throttle response got better, gaining speed got easier, so i gave it some gas and this time it started hesitating at 0.3~0.4 bar.
Seems the hesitation is not dependent on RPM.
Not an overboost issue either, i can't imagine my TD04 overboosting at 1.7k RPM.
Neither is it a fuel issue because it does the same on both LPG and gasoline.
Looks like that leaves only the ignition at fault and the more i look at it the more i fear it might be the DIC.
I guess it was about time it let go, it's the original DIC and the clock shows over 316k km, how long do these usually last?

Also the misfire got so bad i don't even get boost above 1bar, surprisingly yet - still no CEL.
Oh yeah and forgot to add that it idles just fine, no funny noises.
 

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IME DICs usually get iffy around 200k km. I would not expect one to last more than 250k km. If it did, that's just crazy luck.
 

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'96 SAAB NG900 SE (R.I.P.), '99 SAAB 9-3
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Discussion Starter #19
More news in the bag.
First, a correction. The DIC is NOT the original DIC. The date code says 19th week of 1998, but my car was made at the end of 1996.
Also the DIC is 100% bad. How am i so sure you ask? because i pulled the plastic cover off and immediately noticed a cracked open capacitor.
It's the blue square capacitor, the markings are not very clear but i think it's rated for 1µF 630V.
The board is hard potted and normally these are assumed to be unfixable, mainly for three reasons.
  • The potting is opaque so you can't see the board/components.
  • The hard potting is hard to dig out and makes it easy to damage the board in the process.
  • Unless someone has done it already you have to dig all the potting out because you don't know where the fault is.
This time the fault is obvious and digging the bad capacitor out would be trivial. Since i'm an electronics hobbyist i wouldn't have trouble finding a replacement capacitor in my spare parts.
Anyways, i'll bring the DIC to the bench and see what i can do. I'll let you guys know how it turns out.
 

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'96 SAAB NG900 SE (R.I.P.), '99 SAAB 9-3
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Discussion Starter #20
Guys i think i've done it.
Kinda jinxed myself by saying that i won't have problems finding a replacement capacitor because i didn't have any.
As a temporary fix i settled for two 1µF 450V caps in series because the original was X2 class, which are designed to fail open circuit, meaning that whatever the application of that capacitor was the engineers did not want it to fail short.
But i'm still not sure, since i only think i've fixed it because i did an oopsie...
Before i pulled the DIC apart i gapped the plugs to 0.75mm so it might very well be that it's the smaller gap that made the difference.
Anyways i'll be heading to the local TV repair shop to see if they have any suitable caps.
Also the car absolutely goes now, just found out that one of my neighbors has a big old lathe so the king cobra upgrade might be not that far ahead. :)
 
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