Hey guys new to the site been reading a while here is i just bought a 88 formula350 178,000 for 500 its been sitting 9 years i drained tank new fuel pump and filter and full tune up new temp sensor and cleaned maf hit the key it fires up then dies if u play with throttle a little after it popps back through intake it will idle but hit gas and dies after about 20min of running idle drops to bout 650 check engine light goes off and car pures like a kitten with no problems left fan also comes on with key and can not pull any codes even tho check engine light is on till after 20 min or so it is also a one owner car a woman and does not apear then anything has been tamperd outside of stock any help would b great im stuck

 

The fan coming on with the key sounds like a bad ecm or someone required the fan. You don't state if this is efi but it would be a good idea to have your injectors serviced or replace them.

 

I was hopeing the later on the fan or maybe stuck in diagnostic mode its a 88 with 5.7 tuneport i thought the injectors but would they jus suddenly start fireing fine after about 20 min because after that is runs great no issues thanks

 

Since the check engine light is on and goes off other than normal operation light on until start sounds like a bad 1227165 ecm. Running injector cleaner to help clean the filter baskets wouldn't hurt but sounds like the ecm is the primary issue. Especially if you can't pull a code 12 if that's the case.

 

You can see the ecm grounds the green/white wire at 226f or so. If it's wired correctly the ecm would not run the primary fan until then.

 

I ran seafoam in 5 gal of fresh 91 fuel but havent ran on road tires are dry but running in garage almost empty now th check engine light stays on till after the idle smooths after about the 20 min mark and no not even a 12 code will display. Sry not up on all sensor lingo im used to the old 70s i know what the ecm is but whats 1227165 ?

 

The 165 is the ecm (electronic control module) service number it might have a superseded number like 16198259 , 88999194 or cardone 77-7165

 

Ok do u have or kno where i can get a wireing diagram of the ecu so i can check grounds and connections before 400 on a new ecu thanks

 

Wow where are you looking at a $400 ecm that's nuts
https://m.ebay.com/itm/Engine-Contro...%257Ciid%253A1
http://tpiparts.net/1227165_pinout_diagram

 

Oh wow i was looking at autozone lol

 

The grounds are behind the passengers side cylinder head. But with your symptoms sounds like a bad ecm to me. I have soaked injectors in sea foam and wasn't impressed bye the amount of varnish it can or can't remove.

 

What do you recomend for the injector cleaner

 

Chevron or stp

 

Thanks would u happen to kno what sensor is inbetween the back two plugs on the passenger side its a single wire single pin connector i just found the connector is broke

 

That's the secondary fan switch. Same as knock sensor connector.
https://m.ebay.com/itm/GM-Knock-Sens...%257Ciid%253A1

 

That wouldent b keeping the fan on would it?

 

If that connector is grounded the secondary fan will kick on.

 

Ok thanks for all your help im gonna put the ecm in in the morning just orderd it i will let you kno what happens

 

Disconnect your battery before you disconnect the ecm to avoid electrical static discharge/ voltage spike. You will need to remove the memcal. Blue covered computer chip. Tilt back the white and blue retainer catches. The memcal can only be inserted one way.

 

Thanks i forgot to mention it idles at about 1300 till that 2omin mark and its rich and oil pressure reads 60 dont get bk to normal till that 20 min mark and what is this?

 

That's a vss buffer vehicle speed sensor signal buffer for the speedometer and ecm.
The oil pressure maybe the sender itself or gauge is reading off.
The buffer mounts on a tab on the ecm holder.

 

Ok ill try the oilpressuer sending unit to but it reads norm after hot could that cause it to run the way it does looks like someone at some point has already got into the comp area cuz that was hanging loose in dash and some screws where missing on pannel

 

Ok replaced ecm now car wont start is there some sort of programming i have to do

 

Did you swap in the computer chip ?

 

Yes and last night before i took the old ecm out i tapped on it with my hand while it was running to c if it was bad and it killed the engine and wouldnot start bk up so i figured that ment it was bad now that new ecm is in it still wont start but i can get a 12 code now

 

Check the fuse next to the battery I think it's a 20amp fuse.

 

Its good

 

Start back at the basics, do you have spark. Do you have injector pulse (noid light).
Fuel pressure good.

 

It will fire and then die immediatly

 

Could it have killed a sensor like iac,tps or icm

 

You might want to pull a few plugs to see if it's flooded or dry plugs.
To clear out a flooded efi hold the gas pedal to the floor and crank. Sounds like lack of fuel injectors plugged . The ninth injector works on cold startup it might be the other eight not firing.

 

Ok im just confused because it was running until i tapped on the old ecm then when i tried to fire up it did what its doing with thus new ecm

 

Awsome it was flooded got it running but still rich only code is a 34 low voltage to maf i believe i already cleaned maf what els could it be ur help has been amazing i thank you so much the ecm would have been last thing i replaced u saved me so much time and money

 

http://www.chevythunder.com/maf_code_34.htm

 

Thank you so much getting a 33 and 34 maf must b bad looks like jus a lil more money that must b whats making her run rich thank you

 

Actually intake hose wasent tight just tightend it and no more code

 

Great progress

 

Thanks again couldent of done it without ya

 

Welcome