Need to figure out why LX9 runs poorly

[jmgtp]

I'm at a loss on what to do. First here is what I'm working with:

LX9 swapped into 1991 Grand Prix with Getrag 284
External crank trigger OBD I ECM, which has gone through a lot of tuning
CPS is set at 0 degrees timing (the crank trigger is adjustable)
3400 exhaust manifold
New 3 way cat converter, 2.5" pipes, 97 Grand Prix GTP stock mufflers
3400 throttle body and fuel injectors
43 psi fuel pressure at WOT
Stock heated LX9 o2 sensor

How it runs:
Idle is smooth on the tach. At idle engine has a bit of a vibration to it though, not enough that I'd call it a shake, but it let's you know its running. In gears 1-4 under 2500 rpm feels like it's missing some torque but its not awful. In 5th gear it shakes pretty violently at anything under 2500 rpm. WOT performance isn't terrific, but not awful and I'm sure the old school 3400 exhaust manifolds are hindering all out performance. But that is not my main concern, rather the poor low end torque and the shaking motor. Driving normal above 3000 rpm the motor runs great and torquey, it cruises beautifully at 45 mph in 4th.

I've gone over the entire fuel injection wiring a few times and can't find a problem. Its been through countless back/forth tuning. It holds good vacuum at idle, roughly 40kpa. I gave it new plugs and wires. The old plugs looked perfect in color. I plugged an exhaust back pressure gauge in the o2 sensor port and the back pressure is negligible. I'm at a loss on what to do and looking for any advice.

[Superdave]

LX9's usually idle smooth as butter, are you sure the ICM and coils are good?

Stock 3400 injectors @ 43 PSI really aren't enough for a 3500, at least put the 55 PSI regulator in there so they get to 22.5lb/hr.


Post up your bin file and a datalog...

[jmgtp]

Even at idle the 3400 injectors wouldn't be capable of flowing enough? The idle is stable but far from smooth. Take off in 1st you can tell there is something not right but it isn't too bad. The shakes in 5th have me the most worried. Could it be a motor mount issue? I'm running a solid 3x00 lower mount AND a solid 3.4 DOHC rear mount, so it essentially has DOUBLE the lower motor mount. Up top I'm using 2 lumina dogbones, and a stock Getrag 284 trans mount on the other side. I'd think with all that the motor would be mounted solidly, but at idle there is a visible shake too it, nothing violent but its there.

Here is the latest datalog, it isn't a great one and I can get a better one if you'd like, or if you'd want me to run the motor under different conditions. Need any other parameters? I don't know that I can post the bin since that is something that someone else worked on, perhaps with permission I could email it to you.

Datalog file: 07-11-2011.csv

[WrathOfSocrus]

Are you using Multec 1 3400 injectors or Multec 2? The spray pattern of the Multec 2's probably aren't designed to run at 43 PSI if that's what you have. Add in the better flow from the 3500 compared to the 3400 and you could be throwing a bit of fuel out the exhaust unburned. Changing the tune to adjust probably wouldn't fix it.

I would take Superdave's advice on using the 55 PSI FPR. Or if you still have the DOHC injectors you could probably use those as they are designed for 43PSI and I think they are around 24 lb/hr. I think the spray pattern might be different on them but at least they would be running at proper pressure.

If you are in fact using the early 3400 Multec 1 injectors then disregard the above

[Superdave]

3400 injectors have the correct pattern for the 3500 regardless of pressure. 3.4 DOHC injectors work but have a wider pattern.

At idle it wouldn't make a difference, At WOT you'll come close to running out of injector if you get rid of those 3400 manifolds.


your log is missing a lot of important info, can you post the .adl?


PM me your email address, i may have something that'll help you out...

[WrathOfSocrus]

Injector spray pattern isn't affected by the pressure? I would think it wouldn't atomize the fuel as well with a reasonably lower pressure. I've never really seen anything about it I just thought it would make a difference.

[Superdave]

the pressure difference from 43 to 55 isn't enough to mess with the pattern, i ran DOHC and 3400 injectors at several different pressures back when i was doing injector cleaning.. always similar results.

M1 3.4 DOHC injectors are very wide patterned and do a very good job of atomizing fuel, 3400 M2's are quite a bit narrower and don't make as nice of a fog as 3.4 DOHC's. They are more narrow which makes sense considering the runner shape and where they sit in the path. If i was chasing MPG, 3.4 DOHC injectors would be worth it but the 3400 M2's and L67 injectors are where it's at for power.

[jmgtp]

Guys, thank you for the replies, I'm sorry that I have delays in getting back to you. I've been very busy at work and sitting at a computer when I get home is the last thing I want to do since I'm plopped in front of one all day.

I had to dig through my ebay purchased list to find what the injectors were from. The listing wasnt available anymore but the auction title is "1999 3400 injectors" - so I guess the question is whether or not the 3400 used Multec I or II injectors in 1999. I bought the injectors/rail/regulator as a unit.

I tried the 3.4 DOHC injectors at first and the car ran very poorly. When I swapped in the 3400 injectors it instantly ran WAY better and all the tuning that was done was on the 3400 injectors. Honestly I'm more interested in MPG than all out HP so if the DOHC injectors worked for that I'd be all for it, but like I said, we tried them and it never ran right - the 3400 injectors at least made it driveable. I wanted the Grand Prix to be a reliable and torquey commuter car.

Superdave, I will PM you my email.
I can post the .adl tonight.

[pocket-rocket]

so I guess the question is whether or not the 3400 used Multec I or II injectors in 1999.

I'm not 100% positive, but I think 99 used the M2's. Are they fat like the DOHC injectors or really skinny things with a different connector than the DOHC injectors? If they are skinny with a different plug, they are M2s.

[jmgtp]

Their physical shape is roughly the same as the DOHC injectors, if not identical. They are fat bodied, use the same o-rings, and use the same electrical connector as the DOHC injectors. I believe the plastic body part is red. I guess this makes them Multech I.

I can say that they are VERY different from the stock LX9 injectors, which are very skinny, I believe shorter in height and use a different electrical connector. They also have a 'cone' on the spray end which I'm not sure of the purpose - maybe to 'funnel' the spray to increase its velocity? or somehow improve atomization? Anyway, these are just sitting on a shelf in my garage.

[pocket-rocket]

Their physical shape is roughly the same as the DOHC injectors, if not identical. They are fat bodied, use the same o-rings, and use the same electrical connector as the DOHC injectors. I believe the plastic body part is red. I guess this makes them Multech I.

Yep.

I can say that they are VERY different from the stock LX9 injectors, which are very skinny, I believe shorter in height and use a different electrical connector.

Those would be the M2s.

[jmgtp]

07-11-2011.zip

this is the data file from TunerPro. It wasn't the best log and I can get a new one if someone would like to see it, or see something specific like idle only, cruise only, etc.

[Schmieder]

you said crank trigger is adjustable? Not sure about the LX9 but I just corrected a crank sensor issue. If the 3xCKP isn't lining up with the Camshaft Position Sensor properly, your car will run like crap. My 3xCKP wire was backwards.

If the crank trigger isn't spot on target, the PCM will put Cyl#1 TDC at some other crank angle, screwing up ALL the timing by that much.

Plus, the CKP wire is sensitive and cannot be resting on a plug wire or the alternator case.

Just a guess, I'm a shadetree novice building his own turbo.

[jmgtp]

The crank trigger is adjustable but I have it set at 0 degrees.

The CPS wiring is a used one that I bought. I suppose its easy enough to remove the CPS wiring and inspect it. I'll make that my next course of action.

The car is offsite now while I am working on a Silverado so it might be a week or so before I can try anything on it.

[robertisaar]

in this application, the cam sensor isn't being used.