ok been working on a car the past few days thats doing some really weird stuff, car barely started and when it does its so rich it barely cranks. Discovered the car was using low impedence injectors (its a 2000 olds alero). Car has the GM supercharger reflash, switched the injectors to some other ones I had around 310cc to just try to get the car running. Car still does the same crap starting up. Map readings are way screwed up reading about 70kpa at idle, just driving through a parking lot the map reading will go way into 150ish range, car goes into boost with minimal throttle. Tried 3 different map sensors all did the same thing.
Because the map reading is so high and shouldnt be its dumping way more fuel than it needs to, I cannot seem to tune around this either, played with the injector constant, its like nothing I do has any effect. What the hell is going on here? I can provide logs if needed from HPT
1989 Turbo Trans Am #82, 2007 Cobalt SS G85
Are you sure the wires going to/from the MAP sensor are all good? Do any of them have high resistance (ground, 5 volt reference, signal out to ECU)? That is what I would check if you have tried everything else.
Also what about the bypass valve? I would put the stock tables for the reflash back in with the 310cc injectors, check the bypass, and wiring on the map and see.
FU Tuning
What exactly should i be checking as far as the bypassvalve?
1989 Turbo Trans Am #82, 2007 Cobalt SS G85
The valve should be all the way open at idle, bypassing the incoming air. Do you have a mechanical gauge to verify the vacuum at idle?
Has the wiring been hacked into by anybody previous? I ran into this with a customer's car a few months back. I tried multiple PCMs, and it appeared to be the harness. The customer has since replaced the engine wiring harness and he sid it now runs. I'm just waiting on confirmation from him that he checked the MAP PID with a scan tool and verified the KPA reading before I go back to tune it....
P&P Tuning
420.5whp / 359.8wtq
Low impedance weren't used in 2000 from the factory, odd. Only 1999.0 models had a chance at having low. 1999.5+ were high.
Catalytic converter clogged? When mine went, I kept overboosting with minimal throttle with the supercharger, and eventually it couldn't even go beyond 25mph, and it took forever to get there.
2001 Olds Alero (LD9)
650 whp / 543 ft-lb
@turboalero
No 99 J-bodys had low impedance...they are all high impedance.....other GMs are a different story for 99.
PRND321 Till I DIE
Old Motor: 160whp & 152ft/lbs, 1/4 Mile 15.4 @88.2
M45 + LD9 + 4T40-E, GO GO GO
Like Mike said other 99 GMs can be wierd about injectors. I have seen these ld9 n-bodys: 99 with egr/ w hi imp inj, 00 without egr/ w low imp inj, 01 without egr/ w low imp inj.
But to me sounds like a MAP issue or bypass valve.
QWK LN2 (needs an @ss whoopin) wrote:Has the wiring been hacked into by anybody previous? I ran into this with a customer's car a few months back. I tried multiple PCMs, and it appeared to be the harness. The customer has since replaced the engine wiring harness and he sid it now runs. I'm just waiting on confirmation from him that he checked the MAP PID with a scan tool and verified the KPA reading before I go back to tune it....
Learn from this guy
Don't attempt to tune someone's car that has wiring/mechanical issues. Tell the guy to get the car in good working condition and bring it back becasue something is wrong mecahnically and/or with the MAP/wiring. Also, i'd never try to compensate for a mechanical or wiring fault with tuning if it can be fixed properly.
Car is a 2000, not a 99
I agree Oldskool, I dove headfirst into this one thinking, oh factory 2 bar, ill be done in an hour. Yeaaaaaa......
Harness looks good, no obvious signs of hacking. I do want to hear some more detail on how exactly I could check the map sensor wiring, i do have a multimeter.
What I see at idle is about 10inches sometimes going down to 15 almost on the boost vac guage, its a autometer mechanical, I checked the vac lines multiple times for leaks could find nothing, besides if its just a vac leak the overboosting issue would not happen. Kpa readings in HPT are 67-80 at idle which is way too high and this is causing the computer to run the injectors at 5.6ms causing a very very rich condition, slightest throttle and it jumps to 215 and the pulses go way up to 16 or so causing the car to drop to 10.1 afr, occasionally will quit under deceleration coming to a stop sign.
I suggested clogged cat as multiple people had told me that night, still waiting to hear back if thats been addressed. I don't want to tell someone to get a whole new engine wiring harness if thats not the issue either..
1989 Turbo Trans Am #82, 2007 Cobalt SS G85
I have heard about this too and have the same problem with mine atm. My tuner said that I should switch out to a 4 wire heated O2 sensor for the bank 1 sensor on the header. Haven't got around to doing it yet but As quoted he had a similar issue and that corrected it.
Guess I need to not be lazy and do it lol.
As stated earlier, make sure the mechanical bypass valve is still fully opening when you're idling
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- Sold my beloved J in April 2010 -
How exactly do i test that
1989 Turbo Trans Am #82, 2007 Cobalt SS G85
Rod, you should be able to tell if its open or closed by the position of the shaft coming out of the bypass valve actuator.
thats kinda hard to tell being the whole thing is under the charger and not in sight
1989 Turbo Trans Am #82, 2007 Cobalt SS G85
you don't have an inspection mirror?. basically, if the rod is "in" then the valve is open, and if the rod is fully extended, then the valve is closed, and should build boost.
