1988 gmc sierra hard starting, running rich

[mragoalie]

I have a 1988 gmc sierra with a 5.0 v8. it has a terrible time starting when cold with me having to crank it for around 2 to 3 seconds or longer. once it gets started it runs fine altough it is definetly running rich jusging by the fumeds coming out the tailpipes. i recently replaced the map sensor, this did nothing after i returned the new sensor i checked the old one again by disconnecting it while thhe engine was running and the idle didnt even think about changing. ive check all spark plugs and noticed that the right bank is black with some being coated in wet fuel and the left bank is white. sometimes i can get some decent mileage but other times i somewhere around 9, city driving. any help is appreciated.

[speedygonzales]

More than likely the FPR is leaking which causes rich running and also allows the fuel to drain back toward the tank after shut off.

Next time you try it for the first time, do this:
Turn KOEO for a few seconds then turn the key off and repeat this for about 5 or six times. After the last time go ahead and crank it like normal and see if it starts up quickly.

Do not continue to run it this way as you may have crankcase dilution. Smell the dipstick for gasoline smell.

[mragoalie]

i chhecked the dipstick for a gas smell and i found a fairly strong oil gas mixture smell. what does fpr stand for?

[mragoalie]

just tried to start it like you said and still had the same hard start.

[speedygonzales]

FPR is fuel pressure regulator. Get the oil changed right away. Then you have to pull the TB (throttle body) and get it redone with new FPR and at least have the injectors cleaned.

Incidentally, the ignition may now be a problem for you since it's been running rich for so long. The plugs at least some of them could be fouled. The age of the distributor cap and rotor will not help either.

A routine check of oil level (and smell) will preclude crankshaft problems in the future.

[mragoalie]

alright thanks alot for the help i could not figure it out. ill try that.

[mountie]

Also, check your oxygen sensor. It is the only sensor that adjusts idle at start up, and it takes a long moment for it to react. ( A good running '88 truck will have a slightly high idle at start up, then as the sensor "senses" , ..it 'kicks in', and your idle drops to the correct rpm)....

New vehicles have multiple sensors, so your idle is "corrected" immediately at start up. Our older models don't have that, so if it is not operating correctly, you will have the wrong idle.

CHECK ALL OF YOUR GROUND WIRES ON, AND AROUND YOUR ENGINE, AND CLEAN THEM, including your computer chip 'tangs'.. Older trucks have dirty ground connections, and any poor ground connections will FOOL YOUR COMPUTER, no matter what part you replace!!!!

[BigBlocksRule]

Don't forget the intake coolant temp sensor. If it goes out, the engine thinks it's cold and pours fuel into it. Easy test - unplug it and plug in a new one and lay it on the manifold, no need to install it.

[mragoalie]

one more thing it runs extremely shaky when completely warmed up and stop lights but when cold it runs with almost no shake.

[mragoalie]

ok i just measured tha voltage on the tps and im getting around 0.2 v at idle and when i ste[p on the gas it goes up to around 0.4/0.5v

[ChevyTech]

Originally Posted by mragoalie

ok i just measured tha voltage on the tps and im getting around 0.2 v at idle and when i ste[p on the gas it goes up to around 0.4/0.5v

This is not within the specification.
Double check your test.
Minimum is .5 volt on most applications.
It should go over 4.00 volts at wide open throttle.

Below .2 volt at idle is where it usually will set a trouble code for the TPS.

I agree with BigBlocksRule that you should test the coolant sensor.

The computer uses the coolant temp to determine how much fuel to inject and how fast the idle speed should be.

It is common for these sensors to fail.

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

If you see any coolant leaking out the terminals replace it.

If the terminals in the connector are corroded replace the “pigtail”.

On the TBI trucks the sensor screws into the intake manifold, on the front passenger side, by the thermostat housing.
On the Vortec big block it's on the front of the intake ahead of 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. or 45 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.