9 1/2 miles per gallon

[DaveFromColorado]

I gotta figure out what the hell is wrong with my Z-34.

 

Currently, it's only noticable issues are that it's runnin' way too rich on acceleration (black smoke out the talepipe) and that the trans never goes into converter lockup (it used to, however, I think I may have f'd up a wire on there myself - haven't looked yet)

 

The car has never been a real champ with the gas milage (as many of you know what the front end looks like) but 9 1/2 miles per gallon, I may as well be drivin' a full-sized 1-Ton dualy pickup.

 

I haven't even started lookin' at poss. wrong things with it yet, I will be doing that probably this commin' up weeked. I can hear a vacuum leak under the upper plenum (fuel pressure regulator vacuum line maybe?) I replaced that line because it was cracked when I changed my intake manifold gaskets (perhaps I did a lil' somethin' wrong on there) and I've fixed all the other vacuum lines I can get at from the top.

 

if anyone has any ideas as to where to look just to help me out, it'd be surely appreciated.

 

Thanks in Advance!

 

--Dave.

[DaveFromColorado]

Oh yeah ... it's a 92 Lumina Z34 (LQ1) with the 4T60-E trans.

 

(altho I'm sure y'all could've guessed that)

 

--Dave.

[slick]

Stock ECU chip, right? Have you tried pulling any codes yet?

 

Theres soo many things that can cause bad gas mileage. Here's a decent list of stuff to check.

 

Faulty O2 Sensor

Bad Catalytic Convertor

Faulty MAP sensor

Vacuum Lines

Intake Gaskets

Dirty Air Filter

Fuel Filter

Leaky Injectors

Leaky Gas Tank(hey, it's a maybe LOL)

 

I'd just start with the basics. I know your damn good with cars, and I bet it won't take you long to figure out whats wrong.

[DaveFromColorado]

Stock Computer, with the BHAK chip. I put the upgraded chip in because it was the only one at the junkyard and I smoked my orignial chip tryin' to resolder it so I could put in my live programmer.

 

I'm thinkin' vacuum leak to the regulator, but not 100% sure.

 

 

I get an intermitant O2 code, too rich - this may be a symptom of the problem

No Catalytic Converter

Map sensor checks out (per the scan tool)

All my other vacuum lines I can get to are not leaking

New Air Filter

I'll try replacing the Filter (I always forget about the fuel filter)

Injectors hold pressure in the rail

Checked the gas tank - no leaks (hey, it's a good thought, so I had to check it)

 

I'll be pullin' the upper intake probably tomorrow so I can check that one line to the pressure regulator - I'll also replace my fuel filter, plugs, and oil/oil filter at the same time.

 

Here's an other strange thing, I reported a couple months ago that I would get a stumble at 4k RPM's no matter what gear I'm in, almost as if I'm hitting a rev limitor or some type of fuel cutoff, and I still get that all the time, unless I'm really hard on the car and fire it up cold and take 'er out and rip on her before she's warmed up.

 

--Dave.

[slick]

Here's an other strange thing, I reported a couple months ago that I would get a stumble at 4k RPM's no matter what gear I'm in, almost as if I'm hitting a rev limitor or some type of fuel cutoff, and I still get that all the time, unless I'm really hard on the car and fire it up cold and take 'er out and rip on her before she's warmed up.

 

I've had the same problem in the past. Everything else checked out in the car except for something electrical. The ICM was bad.

[Canada]

Random O2 rich code.....well, thats pretty much verifing that the car IS running rich...although the O2 sensor could still be faulty.

 

You said you had a scan tool (or back probe the purple wire with a DVOM).......look at the voltages. It should vary inbetween 0.100 volts and 0.950 volts or so and move around at a pretty decent rate, when warm.

 

If the voltage coming off the wire seems to be 'stuck' at one end, or a little slow.......you should replace the O2 sensor.....I think a new AC Delco unit is like $75.

 

I have solved a lot of poor fuel economy codes by looking at the O2 sensors voltage output, and if funky...replacing the O2 sensor. My Grand Prix was stuck at 0.845 volts for some reason....I was also getting poor fuel economy, although I never looked at any of the DTCs.

 

 

 

 

 

 

 

I've got to ask.......the injectors are the correct ones for the engine, correct?

[DaveFromColorado]

I've got a spare ICM at my parents house, not sure if it's good, but I'll swap it and see what happens -

 

I'll watch my O2 sensor today to see how quickly it responds, that's a good thought. I may just end up replacing it.

 

I'm a lil crunched for time, so I'm gonna be workin' on my car on saturday, so I guess I just have to put up with it's gas-hoggishness till then.

 

--Dave.

[DaveFromColorado]

Whelp, my fuel pressure gauage decided to die yesterday ... so I'll be getting a new one of those.

 

I hooked my good (snap on) scanner up to my car to see what the car was doing, and I'm gettin' code 44 - lean exhaust, the voltage on the O2 sensor is staying on the extremely low side, ranging between 60mV to 128mV and no higher - 0 crosscounts, but the computer is seeing "rich exhaust" for some reason (this is why I was confused about what code it was seeing, as I hadn't noticed the code, only what the cheap scan tool I was using at the time was telling me)

 

13 minutes of run time, and it didn't go into closed loop, stayed open the whole time, engine temp made it up to 222 degrees so I know* the car was warmed up.

 

I do however think I found my vacuum leak (or where it sounds like it's commin' from) on the EGR valve, when I replaced the intake manifold gaskets, I tried to get away with using the old EGR valve gasket - I think that just cought up to me.

 

I'll keep you guys updated.

 

--Dave.

[bartonmd]

I don't mean to state the obvious here, but you didn't unplug the O2 sensor to take these readings did you?? I only ask because, that's what it would seem like from what you are saying... there should be SOME voltage on it (when you're reading mV's, that is the meter lying to you... there's usually actually nothing) and that would make the car not go into closed loop, and think it was lean...

 

Mike

[DaveFromColorado]

nope, the O2 sensor was plugged in, double checked that too, and I was taking the readings directly from the scan tool I was using.

 

I've started workin' on the car and I ended up feelin' like crap, I decided I was gonna finish it on saturday, but I could hardly get outta bed - seems (according to the Dr. I saw yesterday) I've got a touch of the flu - I guess I'll be finishing my poor car on monday.

 

I have however found one other problem - the EGR adapter to plenum gasket was missing a chunk - so I'm guessing that's where I heard the vacuum leak commin' from - which is why I was thinkin' it was the FPR -

 

with as rich as the car had been running, I was also assuming that all the other stuff was working, and that the FPR was just stuck shut because of the lack of vacuum.

 

shouldn't take too long to finish up my car on monday, maybe an hour or an hour an a half, then I'll see how she runs - but for now, my 'stang gets to be my daily driver again.

 

--Dave.

[DiscoStudd]

Did you get the 222* reading off of the scanner (from the CTS) or from the dash gauge? I'm sure you already know this, but the car won't go into closed loop if it has a faulty CTS and it reads low . Back in the day I remember farting around with the CTS on my old Grand Am, where I was jumpering different resistors across the CTS connector. When I had the resistor that corresponded to "low temp" plugged in, the RPM's were high, and exhaust reeked of "richness" (ie, it was in open loop.)

 

Just thought I'd toss that in there ...

[DaveFromColorado]

nope, the 222 was off the scanner, not the dash

 

I am going to replace the CTS anyhow, because I kinda broke it durring disassembly this time (whoops!)

 

I'm thinkin' it was my O2 sensor tho this time - just wonderin' tho, could the fact that it's stayin' in open loop keep it from allowing the converter to go into lockup? I know it used to go into lockup, but it hasn't since these lil' problems started.

 

--Dave.

[DiscoStudd]

Yeah, I'm pretty sure the car has to be fully warmed (closed loop) in order for the TCC to engage. I'm not 100% sure on that, but it does make sense.

 

So how does the O2 sensor look? Ya never know, it might be what's causing the "open loop" problem . It's usually the simple shit like that that kills ya ...

[DaveFromColorado]

the sensor was trashed, I took it out and tested it per the way the manual tells ya to, and it didn't work - so I replaced it. now I'm havin' trouble finding anyone who has the EGR gaskets (felpro part numbers 70791, and 70793) because both those gaskets need to be replaced, once I get those two gaskets, I should be able to get the car back together ...

 

--Dave.

[1990lumina]

My friends Z24 used to smoke under acceleraion, and it got HORRIBLE mileage....hell I couldn't get my Lumina have have such bad mileage even if I bagged it the whole time....anyway, he also had a very rough idle, with pulsing ....he replaced the IAC and O2 sensors and everything is working better now....dunno if that will help or not

[DaveFromColorado]

I'll look at the IAC while I've got her apart, thanks for the pointers!

 

--Dave.