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1988 9KT not running correctly

2K views 38 replies 8 participants last post by  -Saab_Story- 
#1 ·
I'm having a problem with my 1988 9KT, the engine backfires terribly under load/boost. it doesnt even run at full boost. and if I give it full throttle it will hesitate, bog down and load up with fuel and backfire. the check engine light is on so I'm wondering if its the AMM or the O2 sensor. it seems to run really rich because I can smell it in the exhaust and I looked at the sparkplugs and theyre black with carbon. I think thats usually a sign of a rich fuel mixture. Ive been trying to figure out what the problem is since i got this car back in october. I did pull the engine out to replace some seals and stuff. the car ran ok when I got it. the only other thing that I replaced was the Oxygen sensor when I got the engine back in because the wires were cut and spliced back together by someone else. I did get the oxygen sensor from a junkyard from a car with almost almost 140000 miles. any input would help. thanks

kyle
 
#2 ·
My car is in the garage at the mo. Similar sort of problem, but mine is alot worse I think. Anyway, the guy at the garage said after finally getting it started, that it was running rich, but idling like a bag of poo, so changed the O2 sensor for a known good one, and now it idles smoothly. But he is still working on why the car is only producing 2 psi!! But defo the O2 did certainly help the idle running.

He has changed the DI cassette, O2 sensor, both the fuel ecu ad the DI ecu, AFM, reconnected the APC up, so basically is back to factory standard.
 
#3 ·
well I changed the o2 sensor and it helped a little bit in the top end. but it still smells like its running rich and still backfires under the 4psi of boost. I dont understand whats going on. I tried changing the AMM and that didnt work either. so now I have 3 AMM and a car that still doesnt run worth crap. Im wondering if it could be bad fuel though. I dont think that would make the car run rich though. any more input would be great. thanks

Kyle
 
#6 ·
Used O2 sensor not a good bet. However, have you checked the vacuum line to the FPR? Also, if the diaphragm in the FPR breaks you get raw fuel dumped into the intake through that vacuum line automatically. The FRP takes intake pressure and leans the mixture if the intake is under vacuum. As the throttle is opened or boost develops the FPR diaphragm closes progressively to increase line pressure to the injectors for full throttle or high boost enrichment. If busted you get enrichment all the time.

The other obvious culprit is the cylinder head temperature sensor which needs to work to cause the ECU to stop the cold start enrichment program as the engine warms up.
 
#8 ·
well. the vacuum line to the FPR is okay. the FPR looks like it was dropped because it has a big dent on the fuel side of it. I used a vacuum testor to check the vacuum diaphram and thats okay. Im not sure about the dent on the side of it though. I put some NGK sparkplugs in and that helped a little with the misfiring probably because I spent 20 minutes gapping them perfectly. it seems like the car runs rich at idle but leans out at higher rpm. I wonder if the injectors are dirty? maybe that would cause the misfiring? I dont know how to check the engine temp sensor but it makes sense that it could be the culprit. I wonder why im only getting about 3lbs of boost.
 
#9 ·
I just rang the garage where my car is at. He exchanged my Forge dump valve with the standard re-circ valve, to see if that was leaking off pressure. Unfortunately, that didn't do anything. He has practically changed everything except checked the FPR for now. So I guess thats the next step on the list. Then the engine temp sensor after that. Is there anything else to do? Car is still only getting about 2 psi boost. :(
 
#10 · (Edited)
I tried changing the sparkplug wires because maybe the old ones were cracked and were grounding out somewhere causing misfire. that didnt help so I got the spark plugs that saab recommends and a new thermostat because the old one was stuck open. that didnt help either so now Im out $65. :(. when I reinstalled my engine I put a straigh pipe where the catalytic converter went because it had a large 4" hole in it. do you think that the engine needs the backpressure from the catalyst to run correctly? I know that full 3" exhausts are sold with a catalyst bypass. thanks

Kyle
 
#16 · (Edited)
so, today I replaced the engine temp sensor. it didnt help :( then I tried newer fuel injectors. didnt work:( then I tried another ECU from the same year and same model. that didnt work. actually it ran worse with that ECU. I just dont understand whats going on here. is it possible to pull fault codes from my car? or will the ecu not support that?
 
#17 ·
I taLked to one of the saab shop guys in my town and they said something interesting. they said that the distributor rotor could be bad. so im going to look at it tomorrow. Well I figured out some new problems. and theyre the worst problems of all... wiring.:( explain this one... when the key is turned off and the headlight switch is on, if you press on the brakes the headlights will turn on and if you let off the brakes the headlights will turn off. also heres another brain buster... when im driving on the highway under boost and I turn the headlights on, the boost will back off a lot and the car will run even crappier than with hthe headlights off. If you can explain any of the problems i will be stunned. Thanks

Kyle
 
#18 ·
I believe that there's a feed from the brake lights to the ECU that makes it back off boost when the brakes are applied, so if you've got weirdness around the brake light electrics then that would explain it :) Check the bulbs for filaments from the sidelights shorting across to the brake light filament and stuff like that.


Cheers,
Robin
 
#20 ·
There is a feed on this just a few days ago & all this could be connected.

Brake lights come on = ECU cuts back to base boost
When you get multiple electrical functions working together then it usually means something has failed in a component that is common to all the outputs. It can for example be a diode which can fail closed & allow the current to go back through the circuit that it is supposed to prevent. When you get this type of failure you can get some weird things happening (eg your boost) maybe this is also providing a faulse signal back to your ECU
Where to look?
1) your pictogram inside the consul, it has common feeds & diodes
2) there is a box of relay,s that feed a signal to the pictogram to confirm when a light fails
3) your tail light unit has a printed circuit board that can cause electrical cross circuits when it gets corroded

Please also note if you take out the CAT you need to re set your base boost, it could now be high & this confuses the ECU which then negatively adapts, look to backing off the actuator rod by maybe 2 turns & remember to disconnect the ECU during any changes, leave for a few hrs & let it re set itself

02 sensor, the ECU uses this to set the fuel map at low to mid range, then goes onto a fuel map at the high end, if its getting a bad signal from the O2 sensor it will negatively adapt to a safe "rich" mixture
If the knock sensor keeps giving a trigger the eCU will also revert back to a "rich" mixture

Sorry bit of a juggled dump of thoughts, me i,d try a 2nd hand consul & a new O2 sensor
 
#22 ·
-Saab_Story- said:
hmmm sounds like a good idea thanks for your input. but Ive already replaced both:( so should I replace them again? I have also replaced the pictogram you were talking about.
Cripes :suprised; you must be pulling your hair out - worth talking to Mulik ref: thrd
Lower Boost then normal under WOT
Your both working on the same issue ref: the lights / boost otherwise ??? but keep track of "Cause / Effect" am assuming your pulling 2nd hand bits
good luck
 
#24 · (Edited)
I noticed something else could carbon trails on the gap poins on the dist rotor caps be the culprit behind this whole mess? if you look closely at the picture youll see the little carbon trails that the arrows are pointing to. these are caked on all of the points pretty thick and im in the process of trying to carefully sand them off but the carbon seems to have soaked into the pores of the metal.:confused:
 

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#25 ·
Common symptoms of any ignition system break down is, you can "ease the power on" but if you try & load it up it starts to break down so yes.

Please also confirm what base boost your running, if your high on the base boost you can also get confused mid range response, leads to negative adaption & poor top end boost
 
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