87 Chevy truck help

[hoser]

Hi
I have a 87 Chevy truck, 1/2 ton short bed, 2WD 305 engine, automatic trans, Silverado package, this is the first year EFI in a truck? the truck has been in the family since new.

I have had problems with the way it runs for the past few years nobody can figure it out, the last few times the codes were read it said to replace the ECU, now when you plug into the test harness it says it cant communicate with the computer and cant take any readings.

The problem is intermittent, sometimes when you start it up it runs perfect sometimes it runs rough and it feels like its starving for gas, I just changed the oil with 3k miles on it and their is no hint of gas smell you usually smell in used oil, the plugs are white like new, when it runs bad it idles smooth and accelerates ok at moderate throttle pressure if you accelerate hard it stumbles and acts like it is running out of fuel.

At idle when its running bad the injectors are noisey, the first time I heard the noise I had to pop the hood and pull the air filter to see what the noise was because it was a new noise its almost like they were pulsing abnormally, when the engine is running good they are quiet.

I have narrowed it down some, when it is 65 degrees out or colder the truck runs perfect and normal, above 70 and it runs bad, if parked in the garage over night and taken out into 80 degree heat it runs ok until you shut it off and restart, its almost as if the interior gets any heat build up it runs bad more than affected by the outside temps.

I have beat on computer with a wood dowel this had no affect, I have removed the computer taken it out of the metal box, wiggled anything and everything I could see to wiggle looking for a bad connection, I looked over 100% of both sides of the boards looking for something with corrosion or discolored like it over heated, I seen nothing, I removed the "chip" and reinstalled, this did not help anything, I have unplugged and plugged in every wire connection I could find on the truck, I have wiggled, pulled and pushed on all the harness I can find, this didnt help or hurt anything.

I assume something in the harness or computer is bad?

Help, suggestions?

Thanks in advance.

[Captkaos]

1987 is the fisrt year for TBI.
Does it have any codes right now?  Jumper the last 2 terminals on the top right of the ALDL and switch the key to run position and count the flashes.  It always starts and ends with 12.  Let us know what you find.

Have you replace the ECM?  Beating on it can't help it it can damage it.  Taking it apart isn't  recommended either. 

Can you drive it?  What test harness are you plugging in. the GM scanner?

[VileZambonie]

check your fuel pressure- pinch off the flexible return hose from the TBI and road test - see if it gets better.

[hoser]

1987 is the fisrt year for TBI.
Does it have any codes right now?  Jumper the last 2 terminals on the top right of the ALDL and switch the key to run position and count the flashes.  It always starts and ends with 12.  Let us know what you find.

Have you replace the ECM?  Beating on it can't help it it can damage it.  Taking it apart isn't  recommended either. 

Can you drive it?  What test harness are you plugging in. the GM scanner?

Like I said above I cant read the codes, a computer scanner thingie cant communicate with the computer, I read the codes in the past when the check engine light came on (back when you can read them) and it said to replace the ECM this is why I took it apart and beat on it, I got nothing to lose, FYI it still runs...
it runs crappy the warmer it gets outside, at 50 degrees it ran better than it did new.

I have a 90 Suburban with a 350, think it would hurt to swap computers between the two and do a process of elimination thing?

[hoser]

check your fuel pressure- pinch off the flexible return hose from the TBI and road test - see if it gets better.

I will try this tomorrow, I dont recall seeing a flex line before where would I look?


Thanks guys, keep the ideas rolling the next step is to buy a megasquirt and use their harness, abandon the GM harness.

[Blazin]

I might be wrong but I recall somewhere in that time frame there was a recall for the distributors. The seal in the distributor to keep oil out from under the rotor area would fail and cause intermittent problems.
Can't hurt to check and see if you have oily residue under there.

[VileZambonie]

There is a flexible hose just follow it from the TBI towards the bellhousing.

Does the SES light come on when you turn the key on during the bulb check?

[Captkaos]

The flex line is on the drivers side rear of the oil filter, it is braided steel.

[hoser]

Hi again guys..

I took the computer off my 90 Suburban (350) and installed it in my 87 Truck (305) it started right up and ran great on the road test the only thing I noticed different was the idle was way high after installing the Suburban computer, I turned the idle down after getting back from the road test.

More testing to do, when I was working on the truck it was in my shop all night (70 degrees) so now its setting out in full sun with the windows UP and its about 90 degrees out, once it heats up good inside I will take it for another test spin to see if this cures the problem, read above, remember gut feelings were it was a temperature thing, later tonight I will install the old computer into the Suburban and see if it will start.

Does the SES light come on when you turn the key on during the bulb check?

I assume the SES light is the check engine light ? Yeah it works, the bulb is good, it was ON most of the time with the old computer, with the computer off the Suburban installed it works per design, turn on key and the light is on (bulb check) then goes off after the engine is running. This is another clue the old computer is bad?

On a side note maybe its related or unrelated? The "you left the key in dummy" tone alarm is ON all the time you have the door open keys in or not, I had let my son use my truck a few weeks back and noticed this after he got done with it, I doubt it had anything to do with him I think he is just unlucky lol.

Has anybody seen this before, what is it trying to tell me?

Thanks again...

[VileZambonie]

Well does your interior light work? If so does it stay on while you hear the chime module? If not check the key ignition cylinder contact. You'll need to remove the wheel and just pull it out.

SES = Service Engine Soon same as check engine light. If it works during the bulb check you can retreive DTC's by jumping the A&B terminals in your data link connector by counting the flashes of the SES light.

There is no idle adjustment on your truck you shouldn't have messed with the idle stop screw. Set the TPS to .55v and disconnect the battery for a minute then retry it and see what your idle speed ends up at.

[hoser]

Well does your interior light work? If so does it stay on while you hear the chime module? If not check the key ignition cylinder contact. You'll need to remove the wheel and just pull it out.

SES = Service Engine Soon same as check engine light. If it works during the bulb check you can retreive DTC's by jumping the A&B terminals in your data link connector by counting the flashes of the SES light.

There is no idle adjustment on your truck you shouldn't have messed with the idle stop screw. Set the TPS to .55v and disconnect the battery for a minute then retry it and see what your idle speed ends up at.

Hi thanks for the info.

How do I Set the TPS to .55v ?

[Captkaos]

The adjustment is in the 2 bolts that hold the TPS to the Throttle body.  Loosen them enough to move the sensor and then backprobe the A and B terminal with the ingnition on, but not running.  Move it to where you get .55V.  If you have scanner software you can just plug it in and do the same thing.