ZStones11

Just curious if anyone could point me in the right direction. I have a 91 z28 automatic with a 305, decided to do small changes to it and my mpg went from 24 highway.. To about 16.
The changes I made were:
Had the heads machined down 20 thousandths
Replaced the stock valve springs with 120 pound ones
Put on a set of headman shorty headers and y-pipe (I did opt to keep the egr crap)
Gasket matched the heads
Replaced valve seals and gaskets on the heads and tpi intake
And finally replaced the coil, cap/rotor, plugs, and wires

After all this my tach now reads higher than it truly should be, never happened before.

Just curious if anyone has any info or can help in anyway, TIA

AlkyIROC

Intake manifold leak?
Incorrect ignition timing?

OrangeBird

iTrader: (1)

I would be looking at what happened to the torque converter's lockup command , due to the modifications described . It may be a direct "cause and effect" such as accidentally disconnecting wiring that did not get put back right . Or it may be something to do with the ECM not tolerating the changes , staying in open loop , and never sending the lockup signal ?

Nothing you've done could affect gear ratio , and the higher RPMs at any given road speed make it an almost certainty that the lockup is not functioning .

(provided , that is , if the engine's RPMs are actually higher , VS the tach reading higher than the actual RPMs of the engine)

Ozz1967

iTrader: (4)

On the surface, those changes shouldn't have that great of an effect on mileage. I'd look for vacuum leaks and ensure that your heads have been re-torqued on correctly. After that, what OrangeBird and AlkyIroc said. All good info there.

Ron U.S.M.C.

I would say that when dealing with exact RPM readings and setting the timing exactly, a Timing Gun like this comes in very handy.

ZStones11

When we timed the engine the tach was reading about 1500 when the gun was reading about 800, which was my normal warm idle area before deciding to do some add ons..

And I have been looking into the lock up, and have been trial and error testing with it. I can get it to where it shifts like it did before this, but at highway speeds it still won't lock up..

What are my options if it's something with my ECM not accepting the upgrades?

OrangeBird

iTrader: (1)

On the ALDL connector , one of the pins connects to the ECM's lockup power and can be a great way to determine if in fact the ECM is or is not signaling lockup .

ZStones11

I'll definitely give that a shot, and my check engine light came on this morning for the first time and as soon as I put in it drive instead of overdrive it went off instantly.. What is the paperclip trick?

ZStones11

Alright, a little update:
I found a thread talking more about problems with the tcc and looked further into that, and made a jumper on the aldl. Going down the highway it would lock it in and do what it should. I also took off the accel coil and put the previous one back on, to see if it could have some sort of effect.. But I'm not sure if it changed anything. The tach was reading a little more realistic numbers compared to before but still said I was running 3200 at 80 when it used to be 2200-2500.. I feel like I'm making some progress but I'm completely at a loss for what to do. Should I replace my tcc and then continue down the checklist of possible problems?

Thank you guys for the help so far!

OrangeBird

iTrader: (1)

Ok , so , if a jumper on the ALDL caused the TCC to properly lock up , that tells you that all is fine with the TCC solenoid & clutch and that it is a problem of the ECM not sending the lockup signal (or the signal not getting there) . Jumping the TCC solenoid has proven the solenoid and clutch are good . Now you need to find out why there is no signal from the ECM . The paperclip thing is where you use any handy piece of jumper wire to jump pins A & B of the ALDL and with key on engine off the check engine light will flash the stored codes in the ECM . It will start by blinking code 12 , one short flash followed by two short flashes , three times in a row , and then it will blink out any stored codes . You may see three short flashes followed by four short flashes , this would be trouble code 34 and so on . Any codes found could be another step in troubleshooting why it's not locking up the converter . Remember , the ECM needs all of it's conditions proper before it will command lockup . Anything missing like for instance the VSS or even the 4th gear pressure switch (in the transmission's valve body) will cause no lockup . It's gotta know how fast it's going and that it's actually in 4th gear before it locks up . Also , there is a switch on the brake pedal , normally closed when the pedal is not being stepped ion , that opens the TCC circuit when you apply the brakes , even something as simple as this switch being out of adjustment can kill the TCC functioning . Do you have a wiring diagram of the entire TCC circuit ? If not , the site "AustinThirdgen" has all the wiring diagrams which will be helpful to your troubleshooting as well .

I will attempt to add a link to the wiring of your ECM . If this link works , you will see the circuit of the TCC solenoid and it's connection to the brake switch . Notice also the "4th gear clutch switch" as its called that connects to the ECM , this is the switch I mentioned above . Note also that the TCC solenoid is provided with +12V whenever the key is on and the brake pedal isn't being pushed , and it's the ECM's responsibility to ground the negative going lead to complete the circuit .


Ok , so , my direct link didn't work ... If you search around at www.austinthirdgen.org you will find the wiring diagrams hosted on that site .

ZStones11

Ohh, I used to have the actual thing you plug in to read those and a book with it, but I left it in my rs when I sold it but I'll definitely get on that tonight or tomorrow early and get back to you when I more than likely get stumped on what the error codes are telling me, once again thank you so much for the help!

ZStones11

Alright the codes that came up were 42, and 45
42- fault at electronic spark timing circuit
And
45- o2 sensor rich
Where can I go from here?
Sorry for asking so much.. Just completely at a loss for what to do

OrangeBird

iTrader: (1)

Oops , sorry , hadn't noticed your responses till now .

Anyway , the code 45 , O2 rich , is to be expected if doing work that changes the flow of air/fuel through the engine . You have added headers and now must tune the ECM to accomodate that change . Our ECM's will not "self learn" to that degree , major changes require major programming changes to take advantage of the increased airflow . You may want to look into things like "ECM tuning" and "prom burning" as it sounds like that could be in your future . The code 42 EST is usually either a wiring failure or an ICM or ECM failure .

Just curious , have you established for certain if the lockup is working or not ?

ZStones11

The o2 code came up when I ran the car open headers for a day to get myself to work.. After that it didn't come on.

The lockup did engage when using the jumper and sometimes even after taking it out.. But now I'm on to different problems.. -.-
Are proms easy to do?

ZStones11

So now I found out that my vats has decided to crap out on me.. Ontop of all of this stuff..

But on a side note, could a vacuum leak anywhere cause my tach to be off.. And at the same time effect my lockup from not working properly? Or should I just work on getting it to start and slowly solve problem after problem :/

ex-x-fire

Is the engine getting up to operating temp?