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Automotive Computers

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Merlin
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Automotive Computers

Postby Merlin » Mon Apr 24, 2006 7:25 am

Do we have anyone on the board that knows anything about swapping later model engines and computers to an earlier model vehicle? A guy took my 1991 good running wrecked S-10 2.8L and put it all in a 1982 S-10 with a blown 2.8L engine. (including 1991 throttle body) We can't get it to run. The fuel pump puts gas up to the throttle body and the plugs has very good fire, but it won't hit a lick. I don't see any gas coming out of the injectors to the throat of the throttle body. (am I supposed to?) If anyone is interested in answering this post, please put it into the simplest language that a fence post can understand. I know where the switch key and steering wheel is, but I am learning all the time and willing to learn more. The Chevy dealership wanted over $700.00 to fix the blinkers in my Silverado, so I guess they all could retire on good pensions if I let them fix this. Thanks.

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Jack fowler
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Postby Jack fowler » Mon Apr 24, 2006 10:13 am

Merlin,

I should be able to help you with this one.

First, you said you switched the ’91 engine to the ’82 truck. Did you change the electronics’ and the fuel tank/fuel pump from the ’91 to the ’82? The ’82 was a carburetor engine with different fuel/electronics set up.

I would think the easy way out would be putting the carburetor application on the ’91 engine. (Same engine).

All the service manuals back then were paper. Now they are in the web, but it only goes back to ’93 or ’94. I have a ’91 book I gave to my dad, but he’s four hrs. away. I’ll need it to tell you what circuits to “trouble shoot”.

To make the ’82 truck fuel injected you need all wiring harnesses, electronics’and fuel applications off the ’91.

I’ll try to get back with you tonight, (If I can).

Jack

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Postby Merlin » Mon Apr 24, 2006 11:10 am

Thanks Jack. Yep, he put the computer, gas tank, and wiring harness in the 1982. The 82 also had a throttle body but it was set up different than the 91. He said thats why he had to change the throttle body from the 91 to the 82. He even cut nice holes in the firewall to accommodate the computer. I have the Chilton's repair manual from 81 thru 94, but I can't make heads or tails of what they are talking about. If someone told me I had to have fire here, or there, and told me where to look for whatever needed testing for fire, I could probably do that. I don't understand why there is such good fire at the plugs and it don't seem to have fire at the injectors. (If it is needed) I have poured gas directly into the throttle body and it "almost" starts. But no cigar. Thanks again Jack.

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Postby Jack fowler » Mon Apr 24, 2006 12:19 pm

Merlin,

I thought the 2.8’s in ’82 were carbureted. The ignition module in the distributor tells the PCM the engine is turning and the PCM paluse grounds the fuel injectors. (No referance,no run)

Before you replace it, let me check back in some of my reference material to show you how do some checks. If you poured fuel down the throttle body it should have started. Make sure the distributor is on #1 top dead center.


I’ll be back later.

Jack
Last edited by Jack fowler on Mon Apr 24, 2006 3:44 pm, edited 2 times in total.

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Postby Jack fowler » Mon Apr 24, 2006 3:05 pm

Merlin,

With someone looking at the injectors,turn the ignition key from off to on and see if you get a two second fuel burst out of the injectors and let me know. The reasoning is we are going to see if the PCM(computer) is doing its job.
I'll be back.

Jack

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Postby Merlin » Mon Apr 24, 2006 4:28 pm

We have done that, oh, about 20 times so far, and no gas burst at all from the injectors. Let me tell you the latest. A few minutes ago I was talking to a friend on the phone (he lives off) and he told me something about the injectors needing a "pulse" firing. There is a 3 prong female plug hanging loose without anything in it, about 10 inches away from the injectors, and one of the holes pulses (by test light) as the engine is cranked. It is a different kind of plug than any injector connection I see though. There are 2 plugs on top of my injectors with 2 wires each. Only 1 wire is red (if that means anything). The distributer wasn't removed, and I've checked the firing order a few times. There is very good fire to the plugs also. Thanks Jack for fooling with this mess.
Oh, I finished overhauling my Cub Saturday and fired it up last night. Runs but now I have to tune it up.

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Postby Jack fowler » Mon Apr 24, 2006 8:21 pm

Merlin,

You got me with the three prong female connector. It’s been awhile since I worked on an early Chevy throttle body. The only thing I could think it is; the primary coil connector that connects to the ignition module at the distributor. One terminal is 12 volts, the two center terminals connects to the ignition module and one terminal goes to the instrument panel tachometer. If that’s not connected you have found your problem

Ok… with the diagram attached http://img.photobucket.com/albums/v688/ ... oject1.jpg [/url] (I hope it’s plain enough to see) this is what I want you to do, to diagnosis your no start. (Ignition on) First check the ignition 15 amp. fuse I have circled.(Next)Remove the connector off the fuel injectors and use your test light and see if you have 12 volts at the red wires. Next check the (Computer) ECM/Ignition fuse and sees if it is open. If it is not remove the ECM (Computer) connector and see if you have 12 volts at terminal A6 circuit 435 grey wire.

If all that checks out next, disconnect the distributor 4-way connector, Ignition on, momentarily touch harness connector terminal ckt. 430 with a test light to 12 volts. See if the injectors pause. The injectors should pause every time you touch the terminal. If the injectors pause you have a faulty ignition module or a bad connection from the ECM to the ignition module.

If everything checks out to this part you need a special tool called an injector test light. Really this is the first test you should do, but if you don’t have the injector test light I was going around it thinking you will find the problem before you need it.

How the systems works is; the ECM (pulse) grounds circuit 467 and 468 (terminals D16 and 14) to complete the path of current (12 volts circuit 448) to make the injector(s) work. The ground on the ECM can only take so much current (10 mega ohms of resistance). If you use your test light to check and see if the ground (circuit 467 and 468) of the ECM is pulsing you might destroy the ECM. The ECM’s are protected by quad drivers and the GM ECM is very resistant to punishment but you know how Murphy’s Law goes.

If the attachment is not clear enough I can send it directly.

I hope this helps. Don’t worry about bothering me, that’s what friends are for.

Jack
Last edited by Jack fowler on Wed Apr 26, 2006 8:25 pm, edited 1 time in total.

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Postby Merlin » Mon Apr 24, 2006 8:55 pm

I may be able to follow that Jack, but let me ask you something. As of a few minutes ago I have access to a complete manifold with a carburetor that will fit this engine with all the hoses, linkage, and anything else I need off it. Would it be just as easy to change it to a carburetor? The bed is still off and I could remove the fuel pump, extend the hose further down in the tank and install an in line electric fuel pump. I appreciate your expertise.

Merlin

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Postby Jack fowler » Tue Apr 25, 2006 8:20 pm

Merlin,

Sorry I didn’t get back sooner…It has been a day…

You can convert to a carburetor. The only issue I can think of, if you have an automatic transmission, the torque converter is applied (for lock up) by the ECM. If the torque converter does not lock up in fourth gear you could have an overheating condition. If the vehicle you’re removing the parts from has the electronics you can use them as well.

Make sure you get the distributor, all linkage and the transmission line pressure throttle valve cable if you have an automatic transmission. You’ll be ok with the in-line fuel pump. Try to get it as close to the fuel tank as you can. Vent the fuel tank either through the fuel return line from the old set up (with some sort of filter) or try to find a vented fuel cap. The reason for that is if the old evap. system canister purge valve would close somehow, the fuel tank would collapse from vacuum.

Try to go over your system one more time. I feel the ECM is not powering up via the ignition on (B+) or ignition off (B+) 12 volts. If you turn your ignition switch to the on position on that era GM system the fuel pump should run for two seconds and the fuel injectors should pulse for two seconds.

This is how the electronics work on that era (GM) vehicles….

Terms: ECM – Engine control module
ECT- Engine Coolant Temperature sensor
IAT- Intake Air Temperature sensor
TP- Throttle Position sensor
MAP- Manifold Absolute Pressure sensor
ICM- Ignition control module (inside the distributor)
PROM-Program read only memory
RAM- Random access memory
When the ignition switch is first turned ON, the fuel pump relay is energized by the module (ECM) for 2 seconds. Note: that era GM system had a fail safe with the fuel pump wired through the oil pressure sensor to make the fuel pump run as long as you had oil pressure. (I think that’s why you have fuel to the throttle body) If you turn the key to the on position and the fuel pump runs for two seconds, the ECM is working.

Starting Mode

When the key is first turned ON, the control module(ECM) turns on the fuel pump relay for two seconds, and the fuel pump builds up pressure to the throttle body. The control module (ECM) checks the Engine Coolant Temperature (ECT) sensor, the Intake Air Temperature (IAT) sensor, the Throttle Position (TP) sensor, the Manifold Absolute Pressure (MAP) sensor, and the ignition signal. The control module determines the proper air to fuel ratio for starting. This ranges from 1.5:1 at -36°C (-33°F) to 14.6:1, at 94°C (201°F) running temperature.


Run Mode

The run mode has two conditions: Open Loop and Closed Loop. When the engine is first started and engine speed is above 400 RPM, the system goes into Open Loop operation. In Open Loop, the ECM ignores the signals from the oxygen sensors and calculates (by the PROM in the ECM)the required injector pulse width based primarily on inputs from the MAF, IAT and ECT sensors . The system will stay in Open Loop until the following conditions are met:

The oxygen sensor has varying voltage output, showing that it is hot enough to operate properly.
The ECT sensor indicates above 80°C. (160° F)
A calibrated (via the PROM) time delay has elapsed after starting the engine. This delay allows all sensors to stabilize.

When these conditions are satisfied, the ECM goes into Closed Loop operation. In Closed Loop, the ECM adjusts the calculated (via the RAM) injector pulse width for injectors based on the signals from the oxygen sensor.

Hope this helps and I didn’t misspell or misused any words… it has been a long day for me….

Jack Fowler
Last edited by Jack fowler on Wed Apr 26, 2006 8:34 pm, edited 2 times in total.

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Postby Merlin » Wed Apr 26, 2006 7:28 am

Thanks Jack. I am going to try to test it per your instructions before I do anything else. It's been storming here and a friend is bringing his Cub over today to overhaul it and I have to help him, so it will probably be a few days before I can get to it again.

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Postby Dale51 » Sat Apr 29, 2006 6:28 am

The only thing that comes to mind is that a wire did not get hooked up
& it sounds like a ground wire.
You may be further ahead to take it to a good garage with a scan tool
to see what the ECM is seeing wrong.
There are a number of things that could be wrong & I think Jack will agree
electronics are very fragile & you could have made a censor go bad by hitting it or even the ECM by static electricity.
If it's been broken I did it.
If its not broken wait till I touch it.

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Postby Merlin » Sat Apr 29, 2006 8:29 am

Thanks guys. I'm back from my little jaunt but won't have time to do anything to it for the next few days, but if you think of anything, please post it because I would like to get this Jewell running.

Merlin

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Postby Merlin » Sun May 28, 2006 2:07 pm

OK, heres what is happening now. I paid a mechanic to come out and look at the truck. He spent 4 hours on it trying to find a power lead to the computer. He said it was grounded, but no hot lead to it. He also said that you couldn't just run and hot wire to it and the difference in the 82 and 91 made it where he couldn't pull and codes out of the computer. He's going to look at another 91 and get some information that he needs and come back later. If push comes to shove, he said he would put the carburetor on it but he would rather fix the computer. Me too. Thanks guys and especially Jack Fowler for all the effort you put into it.


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