2.8 MPFI AUTOMATIC 150,XXX miles

hey guys i've been taking care of my 2.8 as much as i can since i've had it but the car just seems to get worse the more things i fix.


the idle seems unsmooth but doesnt change rpm more than 50 rpms and has a slight sputter to it.

after the engine warms up its runs just fine but idle is kinda shitty

a cold start take off makes engine hesitate very badly...
also there is a slight misfire everyonce in awhile

HORRIBLE GAS MILEAGE 10 MPG CITY & HWY


service done to car:

new timing chain
new water pump
new pvc
new fuel filter
new belts
new wheel bearings
new alternator
new battery
new MAF
rebuilt transmission
spark plugs
wires
distributor cap
rotor
vaccum lines
egr gasket
intake manifold gaskets
USED FWD injectors
USED ICM
USED coil(91 camaro 3.1)
USED TPS
USED IAT
cleaned IAC(not sure if good)
sea foam ran through engine

 

check your timing, and sounds like a vacumn leak. spray wd40 around where you think you might have one(throttle body area, with engine running) and if your idle changes, youve found your leak. my cat was clogged and it choked the engine really bad, and the car would seem to have to force itself to run. g/k.

 

my timing was also done but i forgot to add that..

it was at 8degrees but i put it to 12degrees because i read somewhere that an older 2.8 would run better with the timing advanced alittle bit(small power increase from this)

 

a valve adjustment should take car of the tap unless its a bad lifter.and if it hasent been done yet u are deff overdue for a new timming chain.

my niebors car has just over 100k on it and the timming chain has so much slack in it u can rotate the crank 1/4 inch in either direction before it will start to turn the cam.
if urs has enough slack it will deff lose power and gas milage,along with idle ruff

 

the guy i got the car from said the heads were rebuilt at 100k.

the car sat for 8 years after the tranny & rear-end burned up... i've had the car running for almost a year now after repairing everything.

would a bad timing chain cause my mileage to be 10mpg?

what about the injectors?

 

Over time the injectors will clog up and spray an erratic pattern, not spray excessively.
Yes a bad chain will cause a problem because in essence you are "retarding" the cam timing by a few degrees.
The heads being rebuilt wouln't help a bad chain or bad lifter(s).
You could try having the injectors tested/cleaned because they are going to have to come off anyways to get to the route of your problem.
.
Are you getting any codes?

 

there are no codes of any kind... im pretty sure all the sensors are working correctly.


when the car warms up this happens about once every 5 miles while im driving regularly...

 

bump... any ideas?

the timing chain is my last resort due to the amount of work to change it...

 

whistling noise is definitly a vac leak. time to break out the carb cleaner to find it.

 

a

 

https://www.thirdgen.org/service-eng...ht-error-codes

54. Low voltage at fuel pump OR Low voltage at Fuel pump relay OR Output failure at quad driver module

 

im still having my idle problem and horrible mileage even after replacing almost everthing besides the engine.

could this be cause by my CTS(coolant sensor)? my fan turns on when it gets hot.. so does that mean its working?

 

im desperate to get this thing to run right!!! please help

 

As far as I know there is a seperate fan switch for the later 2.8 models.

The clt temp sensor would make a huge difference in gas mileage if it has failed. It will be adding warmup enrichment even when the engine is warm, making it run like crap. In addition, it would never go into closed loop.


To verify that your car is going into closed loop, short the ALDL diagnostic pins while the car is running. DO NOT SHORT THEM BEFOR YOU START THE CAR. shorting them while starting puts a surge through the ECM and it can be damaged. When you short the pins, watch the check engine light. It will be blinking. Do this with a cold engine, as it will be easier to see the difference when it occurs.

At first, the engine light should blink rapidly. This means the car is in open loop. (no oxygen sensor correction)
As the car warms, (about 160 degrees) the light should start to blink slowly. This means that the ECM is now in closed loop, and is using the oxygen sensor input.

Give it a go. If it never goes into closed loop, you found your problem.

 

Does this apply to 350's too?? If it does what terminals do you short?? Arn't these the far right terminals?? Can't you do this with a paperclip? How do you? Thanks

 

Yes, it does apply. I have never done it on a car with the later (not 160 baud) ECM's, but it should be the same.


You need to short the two terminals you use to flash the codes... only do it with the engine running. A paperclip should be fine.

 

These terminals are on the far right. Correct?

 

Yes. The two rightmost on the top row. Terminals A and B on this page

http://winaldl.joby.se/aldlcable.htm

 

i just tested it and the car went from open loop(fast blink) to closed loop(slow blink) within 5 minutes of driving...

the sensor itself looks pretty old and shitty but i suppose its working?

is there any other sensor that could cause my problem? when i replaced my TPS with a used one..

i didnt have the correct multi meter to adjust it so i just adjusted it tilll the check engine like disappeared.. i've drove the car with a very mis adjusted TPS and it runs pretty crappy