92 5.7 GTA auto
AUJP
730 ECM
8D

I have the above with 24lb injectors. Everything ran fine for the longest time. Suddenly I was getting SUV gas mileage. BLM's bottomed out at 108 with the fine fuel and integrators running well sub 108. I changed the programming to 26lb injectors. Even worse. I just ran a 22lb injector program and suddenly I'm closer. My BLM's are actually touching 110 once in a while.
I've checked every known sensor and mechanical possibility and have found nothing wrong.

Why is my ECM running bass ackwards? Bad drivers? Bad ECM? Sticky injectors?
Oh yeah, I'm also starting to get up to 8 degrees retard when I start driving the car. This has never happened until my mpg issues started.

Is it a mechanical or software issue? At this point I'm all the way back to running a stock AUJP bin with only the injector constant changed.

Help

 

Sounds mechanical. Stuck injector??? Did you pull the spark plugs and look at them? Bad O2 sensor?

 

BLM will bottom or almost bottom at idle and lite cruising just substituting 24# inj for the stock 22#.

U sure you dont have something else wrong?

Drastic changes dont occur overnite unless there is an outright failure.

do some investigating and report back.

later
Jeremy

 

My first impression is bad gas. It would have to be really bad though. Thinking out loud here. High detonation combined with a mix that tells the ecm it is rich.... fuel isn't burning off like it is suppose to... Pinging = lower octane... = faster burn time... less stable fuel...

The richer the mix the slower the burn the less timing you need but you are getting detonation... maybe from too much timing. Second impression is something very wrong with the timing hardware. Chain skipped a tooth? Ignition module?

Just some thoughts.

 

I pulled all the plugs. They were all gapped correctly, no damage to the insulators, no abnormal wear or coloring to any of them.

I changed my 22# for 24# 3 years ago, changed the prom, and have had no ill effects until recently. Reprogramming another chip to 22# injectors, even though I have 24# in there helped. I programmed another chip at 21#, again even though I have 24#, and the situtation really didn't change much. Although I have now seen BLM's at 114. Strange. Still plenty of retard though. I saw 15 degrees today.

4 tanks of gas have been run through my car since this started. 3 different stations and all premium. Prolly not bad gas. I just reverified my base timing at 6 degrees BTDC (2 different timing lights). I'll check into the ignition module and hopefully find a problem there. I do have the engine slated to come out over the winter for some beautification and to replace main seal leaks so hopefully I don't need to shut it down early to check the timing chain.
I'm just trying to get this problem fixed before I pull. I'm debating on going 383 but I don't want to start with a less than perfect slate.

Thanks so far guys. Any more suggestions would be appreciated. I'll report back probably Sat.

 

How about a vaccum leak? That would make it run in a VE cell with more fuel than needed.

More thinking out loud...
bad throttle body gasket, or intake manifold gasket, bad transmission kickdown diaphram (vac leak), Fuel pump is going nuts and putting out too much pressure, return line is plugged up or kinked, fuel pressure regulator???

Just some ideas

 

Okay. Have had time to do some extensive research and this is what I have so far:

MAP
IAT
O2
FPR
fuel pump
TPS
changed plugs for grins
balancer not slipped
timing chain
compression (all between 170 and 189) is this high?
CTS
EGR
vacuum hoses
exhaust back pressure from both downpipes
EGR solenoid
coil
pickup coil
distributor cap and rotor
base timing 6 deg. even tried 0 deg for grins, no change

ALL checked out good. Unbelievable isn't it.
Is there any way of testing my ECM? I've had no problems with erasing and programming my EEproms with PP2 so I believe my flash proms are fine.
Maybe test my Memcal? Injector drivers?

This is starting to look more like a general engine/TPI forum thread. I'm hoping it's a prom issue since starting to throw parts at the car would get expensive.

Help O great wizards!

 

you need to reverify fuel pressure. is sounds like you may have had a chunk of crud/rust plug the fuel filter. will the engine free rev up without being in gear, is it only pinging /detonating in gear under load. it is more than likely a bad regulator diaphram now that i think about it(failed to full pressure). i belive 36-40 at idle 45-50 wot.

 

I've run into this kind of thing before on my 700R4 in that the cable has been pulled a notch or two outward from stomping it.
Put a bit more tension on it to see if the increased load will bring the BLMs back inline. The vac line to your regulator having a leak would cause higher pressure so check that line real good.
Both of those can happen without really touching anything.
I would be chasing the 8* retard you are seeing. Probably a good loss of MPG there.

 

The regulator [I]barely[I] failed it's test. Helm's indicates 41psi static and I had 39-40.5 depending on which time that I tested it you want to look at. Pump's good as are the lines and the filter. I've ordered an afpr. Maybe my base numbers for the fuel pressure system were screwed enough to skew the ECM numbers.
BTW the fuel pressure, WOT or not, would not get above 40psi. However it does go well above when I do the pinchoff test on the return line.

I checked my TV cable and it is adjusted properly. And yes, I have lost 8 mpg which prompted me to start the pita troubleshooting.

I'll get back to you guys once the new regulator is in.

 

Maybe your knock sensor has a problem, or something along those lines. If it's retarding a lot, and for no good reason, it would kill economy.

 

Possible. Cold is when it retards a lot. Slight throttle pressure and it starts to retard. Hot it'll only retard when I give a respectable amount of throttle. Kind of backwards don't you think?

The new regulator should be here Tues.

 

something doesn't jive.

If your BLM's are down around 108, then the ECM/code is reducing injector pulsewidth because the nbo2 is saying that the exhaust is rich.

if you did nothing but change the injector constant to 26lb (from your previous known good 24lb), then that should reduce your injector pulsewidth which should in turn raise your BLM's. However you indicated it did the opposite (barely)

Then you set the injector constant to 22lb, which should _increase_ the injector pulsewidth, thus pushing your BLM's lower, however you indicated the opposite happened again (barely).

kind of contradicting.

my prediction:
the O2 sensor is toast, feeding bad data to the ECM and artifically shoving your BLM's down resulting in an overly rich condition and bad MPG. The over-rich condition is probably keeping the exhaust artifically cooler than normal, which is making the O2 sensor condition worse.

the explanation doesn't explain the retarded timing, though. I can't think of anything valid that does, other than a simply defective knock sensor, but they don't usually fail that way. if we assumed the knock was real, then we'd be lead to a conclusion of a lean condition, which doesn't seem likely given the ~20% fuel boost of running at 108 BLM; unless we assume there is a massive vacuum leak.

The fuel pressure you mention is slighty low, but that should RAISE the BLM's, not lower them; so you're looking at another more significant failure than being a pound or two off on the fuel pressure in my opinion.

did you solve this one yet? what came of it?

EDIT: stricken section is incorrect. correct replacements follow:

With the BLM's down at 108, the ECM is pulling 20% of the fuel out, resulting in a 20% leaner mix. This could cause your pinging/detonation and thus the timing retard (the knock sensor is picking up the ping/knock due to lean mixture).

 

Uh nit-pick time , seems like you had it right in other parts of your post, but these two things are askew. When at 108, your PWs are smaller, thus less fuel, not more. So, if he's artificially at 108 (like if the O2 is stuck high, which it's not) then he'd be running actually lean, and that could lead to knock.

And if it's normal, and running at 108, then he's neither rich nor lean in the final output.

If the BLMs want to go further than 108, but can't due to sw limit, then he's still rich until INT catches up.


Viprklr - did the idle MAP change significantly from before to now? If it did, maybe something valve train related (so long as you're sure the timing is set correctly, and that the O2 sensor is working). Have you tried a new O2 sensor?

You still have EGR, and it seems you've checked it, but could it be stuck full on or something?

How about the charcoal canister? Is it loaded with raw fuel perhaps?

Does your check engine light work? Maybe you're in limp home mode (although it's obvious when it's in limp mode usually, and I don't think Limp mode has BLM/INT closed loop working, and probably can't communicate, but I've never tried).

Is it showing low BLMs at high RPMs and high loads too?

 

Absolutely correct, I have updated my post to prevent this from going into the archives as wrong. I was actually wrestling with trying to make the timing retard and the BLM issue make sense by one cause in my head, but I haven't been thinking about tuning / diy stuff in months...rusty. sigh.

 

the charcoal canister can fail and send black gravelly stuff from the inside into the canister solenoid and cause it to stick open. this is an internal vacuum leak but a leak none the less.

 

Have you tried replacing your ecm? Maybe backprobing the O2 pin to see what voltage it is actually putting out? Put a timing light on it to see if it is timing right? My thoughts.

 

I have not checked actual voltage output from the O2 sensor as of yet. I will definitely give that a shot though.

I've lost spreadsheet capabilities with my laptop so I can't say for sure if my MAP changed. Although it is reading atmospheric. It appears as if it's correct.

I checked the EGR. It is moving smoothly up and down.

Charcoal canister is long gone. Sensor is still hooked up to the connector, port on TB is plugged.

CE light does work. Definitely not in limp mode.

I have low BLM's at all throttle positions besides PE.

Timing is correct, 6 BTDC.

NAPA won't let me test drive with a new ECM. Not something I want to purchase for nothing if it turns out the brain box is fine.


Sorry it's taken so long to get back but I got the new AFPR on yet now I can't get the fuel pressure above 36. I've tested the pump up to 56 psi. I just replaced the fuel filter, again, this morning. I think I got a bad regulator. Now I have to wait for a new one.
This weekend i'm doing a leakdown test on this PITA.

I really love my car

BTW - can't test drive my car for a while. Besides it being on storage now (not a big deal) I can't even drive down my road. I believe the plow people took the day off when we got 12 inches of white stuff. Summer tires and snow.......bad combination. At least I even get retard when goosing it in idle.

 

Kind of reminds me of a few posts I've seen about broken valve springs....

 

You know it's getting pretty sad when I have to say that I hope it is broken valve springs. At least this way I have a KNOWN problem to fix instead of chasing down gremlins. Diagnosing sucks.
In chasing down this problem I've broken one of my exhaust manifold to downpipe studs. Now I get to either drill it out or just get long tubes.

 

Looks like the thread just went to a non Prom issue.

Finished up the leakdown test yesterday. Could only get a stable 80 psi from the compressor so at 100 psi the numbers would actually be lower than these.

cyl 1 - compression 170, leakdown 24% crankcase leak
cyl 3 - compression 175, leakdown 34% crankcase leak & exhaust leak
cyl 5 - compression 184, leakdown 32.5% crankcase leak
cyl 7 - compression 180, leakdown 34% crankcase leak
cyl 2 - compression 185, leakdown 34.5% crankcase leak
cyl 4 - compression 178, leakdown 23% crankcase leak & exhaust leak
cyl 6 - compression 187, leakdown 34% crankcase leak & exhaust leak
cyl 8 - compression 189, leakdown 30.5% crankcase leak

I tested one of the cylinders at 92 psi to get a baseline for percentage corrections and came up with (80 psi 34% and 92 psi 20%). If I did my math right, which I doubt, I would need to subtract ~21% from each of these numbers to get a reading at 100psi. Seems wrong to me.

Every single cylinder had black, oily, and gritty residue in the combustion chamber. Looks like carbon buildup but the way I drive the this shouldn't be happening. I would pull the dowel out of each cylinder with this concoction on the end of it.

Could this buildup be causing hot spots in my combustion chamber and pre-igniting my fuel mixture causing the knock counts?
Oh yeah, I don't think I mentioned this but i've also noticed that i'm burning oil now. Blue smoke coming out the exhaust. A wet oily film throught my plenum and runners, and oil on my plugs.

 

The wet oily film in the plenum and runners is from the EGR. If you ran the leak down test without turning it over a bunch of times (until the oil pressure comes up) or didn't put oil in each cylinder before testing it, you WILL get a bunch of leakdown. The rings need oil to seal.

Not sure how you did your math to "correct" for only having 100 PSI, either.....

 

You think the oil film is from the EGR? Maybe a passage is getting clogged? Would that also explain the excessive buildup of carbon/oil/gritty looking crap in my combustion chambers?

I don't believe my method of correcting to 100 psi is correct so the numbers I posted were all done at 80psi. If I was able to get a stable and consistent 100 psi the leakdown percentages would be lower.

For the leakdown test I was turning the engine over by hand. When I did the compression test obviously I was using the key. Each compression number is without oil added to the cylinder. I didn't feel it was necessary to add oil with the compression numbers that I got.

Could what the leakdown test results and the EGR be causing my crazy BLM/mileage issues?

 

I don't think you can do a leak down test without cranking it over so the oil pressure is up. Otherwise the rings won't seal and you'll always have leak down.

It is common for the PCV to pull oil up into the intake tracts. Especially if you have good vacuum. The EGR is a source of exhaust into the cylinders, too. Especially if the motor is running rich.

Sorry - the last post should have been worded better. The PCV put the oil into the intake. The EGR puts addotional soot into the cylinders and frequently carbons up the EGR passages in the intake on our age of cars.