Please Help Me!

[HotRod73]

I've got a 90' Silverado, 350 motor... here is the deal... just bought it from a new ford dealership it was traded in to them and i got it for $500 its a short step side... i just replaced the fuel pump because it was bad... it now runs.. but it runs rich... there is no catylitic converter there is pipe there and goes back to muffler... i didnt know if this would be why, but it smells and its bugging me... i changed the air filter and plugs but this is all ive done... the plugs looked like the truck has been running rich for while...also it smokes... i cant tell if blue or white but honestly looks grey... it does it when i first start it up (figured valve stem seals) but sometime will continue to do it... sometimes will do it when i give it a lot of gas... sometimes it wont do it at all! im lost on both these problems!! any ideas guys???

[ChevyTech]

Check to see if a trouble code or codes are in memory of the computer.

Here are some web sites with the basics on retrieving codes without a scan tool or code reader.

Poor drawing of ALDL but ok instruction + codes
http://www.cfm-tech.com/gm_tbi_trouble_codes.htm

OBDI terminal identification
http://robertpowersmotorsports.frees.../ALDL_plug.jpg

OBDI illustration and instructions
http://www.troublecodes.net/GM/

1985 – 1990 trouble codes instructions
http://www.iroczone.com/specs/TroubleCodes.htm


If it has a code or codes let me know what codes, if no codes are stored the next thing I would do is test the coolant temp sensor that the computer uses.
The coolant temp sensor is one of the criteria used by the ECM to determine how much fuel to inject.

To test the coolant sensor, unplug the wire connector and test the resistance across the two terminals of the SENSOR with an ohm meter.

The sensor screws into the intake manifold, on the front passenger side, by the thermostat housing.

Coolant sensor approximate resistance specifications:
177 ohms @ 212 deg. F. or 100 deg. C.
241 ohms @ 194 deg. F. or 90 deg. C.
332 ohms @ 176 deg. F. or 80 deg. C.
467 ohms @ 158 deg. F. or 70 deg. C.
667 ohms @ 140 deg. F. or 60 deg. C.
973 ohms @ 122 deg. F. or 50 deg. C.
1188 ohms @ 113 deg. F. or45 deg. C.
1459 ohms @ 104 deg. F. or 40 deg. C.
1802 ohms @ 95 deg. F. or 35 deg. C.
2238 ohms @ 86 deg. F. or 30 deg. C.
2796 ohms @ 77 deg. F. or 25 deg. C.
3520 ohms @ 68 deg. F. or 20 deg. C.
4450 ohms @ 59 deg. F. or 15 deg. C.
5670 ohms @ 50 deg. F. or 10 deg. C.
7280 ohms @ 41 deg. F. or 5 deg. C.
9420 ohms @ 32 deg. F. or 0 deg. C.
12300 ohms @ 23 deg. F. or -5 deg. C.
16180 ohms @ 14 deg. F. or -10 deg. C.
21450 ohms @ 5 deg. F. or -15 deg. C.
28680 ohms @ -4 deg. F. or -20 deg. C.
52700 ohms @ -22 deg. F. or -30 deg. C.
100700 ohms @ -40 deg. F. or - 40 deg. C.

[HotRod73]

Awesome! I will check this out. Any idea why I may be smoking? Think it could be rings? It does it off and on... When i start it, it smokes thats why i figured valve seals... but sometimes it will keep doing it at idle and sometimes when i give it gas, and sometimes it wont do it at all... I'll check the codes and see if It comes up with anything...

[ChevyTech]

The early TBI trucks did not have “positive” valve seals on the exhaust valves, they only had them on the intake valves. All the valves had o-rings at the top.

In the dealership we installed the “positive” type seals on all the valves to repair smoke at start-up concerns.

It is very important that the correct technique is used when installing valve seals or it may end up burning more oil then before you touched it.

[HotRod73]

i got a code 43 but my check engine light is messing up...it flashes few times then goes dim and stops... it was trying to show another code... also i do know code 43 said something about not recieving signal from knock sensor?? well there is a big sensor that screws in the block on the rear passenger side that has the wires cut from it,... is that the knock sensor??

[ChevyTech]

Originally Posted by HotRod73

...well there is a big sensor that screws in the block on the rear passenger side that has the wires cut from it,... is that the knock sensor??

Yes, that is the knock sensor.
With that wire cut it should set a code 43 as soon as the coolant temp reaches aprox 189 degrees F., which is when it runs the self test of the electronic spark timing and knock sensor circuit using that knock sensor.

[HotRod73]

so that is the knock sensor?
also... why is my check engine light flashing at first then starts to dim out and then stops? its trying to show me another code

[HotRod73]

why would somoene cut that sensor any ideas?

[ChevyTech]

Originally Posted by HotRod73

why would somoene cut that sensor any ideas?

It may have bigger problems that cause the system to retard the timing so far that the engine has no power.

Cutting the wire causes it to fail the self test so it runs in a back-up mode which will make it run ok, but not as good as if everything worked correctly.

[ChevyTech]

Originally Posted by HotRod73

...
also... why is my check engine light flashing at first then starts to dim out and then stops? its trying to show me another code

Sounds like a loose ground connection or a failing ECM.

[HotRod73]

it does code 12 just fine then halfway though code 43 it starts to barely blink and its dim then it just goes to where you cant see it at all its blank no light or anything...
another question... if the knock sensor is cut... that means the timing is not all the way right correct? would that make my engine run rich? just curious... should i try and connect the knock sensor back up? i know no history on this vehicle i can just clearly see the sensor is cut the engine is very clean so its easy to see wires, casting numbers, etc... and it stuck out thats why i noticed it...

[ChevyTech]

…that means the timing is not all the way right correct?

Yes

would that make my engine run rich? just curious...

If it is running with the timing retarded it will run like it has less power – the driver will accelerate harder – so yes it may seem to be running somewhat richer, but my guess is there are probably a few other things that are not quite right.

should i try and connect the knock sensor back up?

Yes

[ChevyTech]

it does code 12 just fine then halfway though code 43 it starts to barely blink and its dim then it just goes to where you cant see it at all its blank no light or anything...

Fix the cut wire and any other obvious problems but if it still seems rich you should consider that the ECM is very likely bad.

If you can get an ECM at the U-pull-It, for a good price, I would get one. Would should swap the “Prom” (chip) to keep the same Prom with the truck and the ECM numbers should match. Be careful of electro static discharge when swapping proms.

[HotRod73]

its got power i just step on the gas and the tires will start spinnin and no they are not bald their new tires lol ill try and plug it back up and see what happens... i wish i knew why it was smoking...

[HotRod73]

well it starts up and runs fine so i never considered the ecm.. this truck does have 200k miles on it but it is very clean doesnt look like its ever leaked a drop of any fluid its clean i can see all casting numbers etc without having to wipe anything off it

[HotRod73]

it may have been rebuilt at some point or someone may have just taken care of it

[HotRod73]

also whats your opinion on seafoam and what exactly does it do? someone said i should run a can through the motor

[HotRod73]

sorry i ask so much but where is the ecm located? and how do i remove the prom safely

[HotRod73]

Going to check the compression tomorrow what kinda readings would keep me in the clear of a ring job?

[ChevyTech]

well it starts up and runs fine so i never considered the ecm.

It is possible to have a bad ECM and the engine is still able to run. Most bad ECMs I have run across the vehicle still ran good enough that the complaint was a service engine soon light and not a drivability complaint.

also whats your opinion on seafoam and what exactly does it do? someone said i should run a can through the motor

I think it is a good product.
It removes carbon deposits from the engine.
I have used SEA FOAM several times with great success. I have also used GMs TOP ENGINE CLEANER at the dealership many times with good results. The GM Top Engine Cleaner smells just like SEA FOAM to me and I have wondered if they are the exact same product. I have never had any problems from using these products, but if an engine has very heavy carbon, one treatment may not get it all out. My biggest concern is that it is not poured in so fast that it liquid locks the engine.

I pour it in the hot engine at fast idle then stall the engine and let it sit ten minutes.


If using Sea Foam, use the instructions on the can – “When added thru injection or carb”.

sorry i ask so much but where is the ecm located? and how do i remove the prom safely

The ECM is behind the glove box. There are wrist straps you can wear that have aground wire attached to them so you can ground your self so there is no electrostatic “shocks”. The wrist straps are uncomfortable – they make your wrist itch.

Here is what I do:
Disconnect the negative battery cable
Remove the ECM
I get the tools I need to change the prom and the new prom and work on my lap, so once I touch the ECM case I should be “neutral” and I complete the swap before moving. I have prom pulling tools to make pulling the prom easier. The prom is just a chip but it takes a little force to remove and install it.

Going to check the compression tomorrow what kinda readings would keep me in the clear of a ring job?

Your test technique and gauge will affect the pressure somewhat, but you should get at least 140 PSI if it is in good condition. Generally I don’t worry about rings unless I see blow-by. Bad valve seals are very common on these engines.

[jgrh64]

allot of these trucks have a oil drain back problem in the valve cover area pooling oil and getting past the seals. take off covers and using a stiff wire make sue the end drain back holes are clear and there is no sludge buildup either