hey guys im having trouble tracking this one down
91 z28
ho-305tpi (100,000k)
ads chip
she runs nice and strong when cold but once shes warm it looses power like it turned into a 4cyl.....no backfiring or missing,still idles smooth,revs up good in park.
i replaced the tps and fuel filter first with no change,a couple days later put a new msd coil and a new coil pickup in the dizzy,adjusted timing to specs and the car ran beautiful for 2 days now its loosing power again when warm.....no codes!!
i need help man this thing is going for paint in a week or so and it would kill me to have her all nice and shiney and running like ****

 

Next time it's doing that get out and take a peak at your catalytic converter. If it's glowing red then you have a clogged cat.

 

i checked that today,it looked normal

 

I see you added an ADS chip. Switch it out for the original chip and see if that straightens out the problem. The ignition may be getting advanced to far causing problems after the car is at temp.

 

k i will try that......i pulled the cat and checked the timing today and it advanced to 12-btd....so you just may be on to something there!!!!

 

just pulled chip,disconnected bat,reconnect and it still ran the same.....i noticed that the motor feels fairly hot on my face when im under the hood,temp gauge seems to be working if i let it idle she warms upto 120 the one of the two fans kick in,when driving she seems to hold steady

 

Have you done a fuel pressure check? Also, you might want to check the air filter and pcv valve to make sure both are in good condition. So let me see if I'm understanding you correctly. When the car starts acting like a 4 banger, you can stop, put it in park, rev it up, and it's got plenty of power again? If so, you may want to check the egr valve operation and air pump if it's still installed.

 

i have not done a fuel pressure test yet(would that change with engine temp?) i have checked both aircleaners and airway.
yes thats exactly whats its doing after a few min of running.....idle is always steady at 1000rpm in parm and 5-600rpm in gear although in park it feels just a lil rough but not missing.
and thanks for taking the time to help out...

 

The reason I was curious is because the diaphram in the fuel pressure regulator sometimes gets weak. When under load and hot, it collapses. Without a code it's what I would check first. With a code, I'd guess a maf sensor code would be tripping, but those usually cause issues at start up when cold too.

 

ok thx....i will have it tested this week.

 

When you pulled the chip, what did you put back in? the stock one?
Drop your timing down to 8* an see how it runs, with the stock chip.

 

yes put original chip back in,the ads biggie backs on it,i will try again tomorrow......
so far i have replaced
picup coil
coil
tps
cts
o2 sensor
cat delete
fuel filter

i am just waiting to hear from a friend if he has a fuel pressure testor.....and if thats not it i will try the egr delete....beyond that im lost.

i am still trying to figure out why it ran great for 2 days after new picup coil and coil but as soon as i punched it that morning it ran like **** afterwork,checked timing and it had advanced to 12 btd?????????????

 

wait a minute. Your timing jumped from what to what??????

 

Lets try something. With the ignition on, but the engine off, connect a test light to the "F" terminal on the ALDL connector and see if it lights up. Terminal "F" is gonna be the top left hand side of the ALDL connector. If it lights up, press the brake pedal and see if the light goes out. If it doesn't go out, then either you have a problem with the brake switch. Either it needs adjustment or it's faulty and causing the TCC system to malfunction. That might explain the ignition retarding.

 

ok i will have to grab a test light

when i put the new coil and picup coil in i dropped the dizzy back in its place,she fired right up and ran really good,so i took it to my buddys and we set the timing to 6dg btd and it ran awesome for a couple days then i hammerd it in a parking lot and she started acting up....rechecked timing and it had moved to 12dg btd

 

i also tried the egr test tonight by plugging the vac line...took it for a rip (hit a deer,no damage)still the same so i went to check the vac on the hose and there was no vacuum on egr hose.....is this normal?

 

No, that isn't normal. Warmed up the egr solenoid should be allowing th eflow of vacuum to the egr valve. When it's cold, it is grounded by the ecm, which stops the flow of vacuum to the egr valve.

 

In your manual there is a test procedure for the egr valve and solenoid. Follow the test procedure and lets see what happens. Ignore my earlier post about the tcc earlier. We seem to be headed in the right direction. You're still gonna need a test light though, and a vacuum gauge to verify vacuum pressure on the engine side and egr side.

 

ok i have no manuel for my car yet(even though i tell my friends its the first thing to get)but i will do a cross referance on google.....

 

tested egr seems ok.....while i had the plenum off i cleaned up throttle body and did the coolant delete on it,it takes a lil longer to warm up and the car runs great for a lil longer so its def a temp issue

 

Hey for poops and giggles do a compression test on all cylinders.

 

i also noticed the water in my intake was green(antifreeze) but the water in my rad is light brown,ican see the water moving in there so the pump is working and thermostat is good,there is also a slight gurgle noise when i shut her off when shes warm....i just read up it could be as simple as a rad cap or as bad as a headgasket....no water in oil,no oil film in rad and no steam in exhaust

 

With the recent development with the coolant, this should probably be done to rule out a bad head gasket. As an added bonus, we'll also know the compression of each cylinder. Make sure to write down your findings. We'll get back to the original problem, as soon as we're sure this isn't part of the problem.

 

thx guys......i will have it done wed or thur

 

*update*
so fri night after some beers with buddys and they were leaving 30ft strips of rubber in theyre chev truck i decided to rip it up in the zed.....well i after the towns biggest roaster and 150ft of posi(no b.s.)rubber she decided to run beautiful...better than ever and still is.
although i now need some rear tires
thanks for the help in trying to solve this guys it was very much appreciated!!!!!!

 

I know this hasnt been said yet but make sure your distributor is tight... I've had some pi$$ed off newby moments b/c I left it just a tad loose...

 

So what fixed the problem? Putting the car in time out for couple of days.