Idling sucks!

[yellowGT]

For starters, I have a 89 sq body dually with a 5.7 tbi. I have asked in the pre-88 side and im not getting answers. So heres my problem...Truck will turn on but the rpms will jump up and down for a good while then it seems to calm down to a stable rate. I have done the timing including disconnecting the wire, changed the IAC, the temp sensor, maf sensor, etc. One thing I havent done is a fuel pressure test but not sure if I should even do that. I noticed that when I turn the key the fuel pump never stops. There's no tank switch so I dont even think the passenger side tank is functional. I read that the regulator might be bad, the fuel pump is out or even a rubber hose. What do you guys suggest the next step should be. Perhaps SELL IT? maybe even convert to carb.

[ChevLoRay]

Somebody has this....but, I'm thinking that someone will mention fuel pump pressure. Also, and I don't know if this is a possibility, but it seems that in the past topics there was mention made of the pressure regulator spring in the TBI.

Is the SES light on? Have you tried installing the jumper to activate the Check light and count the flashes for the codes it may be holding?

[ChevyTech]

A 1989 TBI does not have a MAF – maybe you meant MAP.

First I would check for codes. If nothing else this would tell you if the ECM is capable of blinking out a code. Being the fuel pump keeps running I am concerned that someone has altered the wiring or the ECM has failed.

Next I would test the TPS voltage. The TPS voltage affects control of the IAC.

If I did not find any problems with the first two tests, then I would test the fuel pressure with it running.

It would also be a good idea to check if the distributor shaft can wiggle sideways. The housing getting worn out is a common failure on these distributors.

[yellowGT]

the light doesn't turn on. i have jumpedthe upper right slots and it does start flashing but how do i know what codes its blinking out?

i guess ill have to check voltage tomorrow or something.

[ChevyTech]

Here are some web sites with the basics on retrieving codes, on OBD1 systems, 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/

Good explanation
http://www.syty.org/old/d&e.html

[yellowGT]

got it now...when it gives you a code it will flash to tell you the first digit then pause and show you the second digit with fast flashes. Right? So like a code 54 it will flash 5 slow time pause and 4 quick ones.


Its the first time pulling codes like this so I just wanna make sure im doing it right.

[yellowGT]

update: The check engine light turned on last time I checked but it wont anymore unless I turn the truck on. The light blinks at a fast rate without pauses. When the turns on it will have somewhat of a choppy idle so after feathering the gas to a steady level it sounds good. Then all the sudden it shuts off. I had my brother turn it on while I took a look at the injectors do their job. Suddenly they stop shooting gas so the truck shuts off.

[ChevyTech]

If the light is blinking quickly with the truck running make sure you have removed the jumper from the ALDL connector.

If the jumper is out of the ALDL and it keeps blinking quickly there is it a good chance that the ECM has failed.

If it does not want to blink out codes this also sounds like the ECM has failed. Check all fuses and check the grounds.

The instrument panel grounds at a screw next to the ALDL connector.

The ECM and engine sensors ground at the front of the intake manifold under the front intake bolts/studs or by the thermostat.

There is a ground wire between the back of the passenger side cylinder head and the fire wall.

Also check the ground between the battery and the fender.

So many people are so bad at testing grounds I usually suggest putting a jumper cable between the engine and other spot and see if it makes a difference.

[yellowGT]

You might be right because like I mentioned before it starts but it shuts off completely. Weird thing is that once the truck shuts off it will not turn back on unless you turn key to off position and then back on. I will check grounds tomorrow. Add some good grounds if I have to.

[ChevyTech]

Originally Posted by yellowGT

Weird thing is that once the truck shuts off it will not turn back on unless you turn key to off position and then back on.

The ignition switch on the lower steering column could be failing and cutting power to some circuits while still feeding other circuits. This is a problem that happens to these trucks.

You can use a test light to probe the terminals at the ignition switch and wiggle the key, to see if it makes, then breaks, connection.

Turning the key off, which cuts power to some ECM circuits, could be resetting the ECM.

[yellowGT]

are you talking about the switch down about half way down the column? where the rod hooks up to?