B2600i won't start

[fire239]

I have a 1991 B2600i 4x4 that i bought as a project. I just rebuilt the front end of the truck and took it for a drive. It has had a hesitation and sometimes backfire since I got it. I have only driven the truck about 25-30 miles since I bought it and pulled it into my garage for the front end tear down. On the test drive, I lost power and it was bucking and hesitating. It then went dead and wouldnt crank. I thought I was out of gas so I put some in the tank. Still no start. I can spray throttle body cleaner into the throttle body and it will run. I checked the wiring at the fuel pump and I am only getting 3-4 volts to the pump. At the fuel relay, I get no reading on my voltmeter from the wiring that I checked per Alldata. I am going to check the computer, but havent just yet. Also, the truck was running rich before all of this happened, actually since I got it. Does this sound like computer problem symptoms? Why would it run on throttle body cleaner if the computer was bad. Is there a fuel pump fuse or something that I am missing?

I rechecked the fuel pump relay harness and found that I am not getting 12v from the ignition. I get 9v from the starter lead when the truck is turned over. No voltage at any of the other leads on the harness. The fuel pump will run with direct 12v via jumper wires, but not from ignition switch.

Also, I did open the computer and saw nothing obvious, but from what I've read that doesn't really mean anything...it could still be bad.

 

[Will]

If it were running rich when it did run I would start with the fuel pressure regulator. Pull off the vacuum hose and see if gas runs out when you have the fuel pump jumped.

Do you have a gauge to put on the fuel rail? Will it run with the pump jumpered? I believe I have a book on that fuel injection system so I could possibly help you with troubleshooting sensors if needed.

We had one of these, bought new in 1992 and sold in 2005. The only thing that ever went wrong with it was the gas tank rusted out. I never even changed an alternator or starter or anything. I never had to do any work on it so I don't even remember what the engine looks like. It was an auto and we used it to pull a small travel trailer and it was really the best vehicle I can remember owning. Very comfortable drive and handles a load of gravel fine too. So I think once you get it sorted out you will like it. Mine ran out of seats when we had twins.

 

[fire239]

The fuel system did pressurize when the fuel pump had a direct 12v connection to it. I'm not sure about cranking because I unhooked the trucks battery and powered the pump with it from underneath the truck. After I did that, I disconnected the output fuel line from the fuel filter and it had pressure and gasoline in it. So, I'm back to no power to the pump. One of the leads from the fuel pump relay of course supplies power to the pump, and I get no power reading there with a volt meter. The relay did check ok with both power applied tripping the relay and resistance ohms test. I'm thinking electrical, but does the ECU somehow control the electrical input to the fuel pump relay?

 

[Will]

I don't know. The diagrams I have are for the MECS which is the system I assume is in that truck. There is a fuel pressure regulator control solenoid and a fuel pump relay both connected to the control module. It looks like they are turned on through the controller but get their power from somewhere else. If there is any power back there, or at the relay, I don't think it is the controller. I would see if it runs with the fp going and then start by locating the relay.

 

[fire239]

Tomorrow I'll try to power the fp and see if it will crank and run. From there, I'm not sure. The way it was running rough and backfiring, smelling gas (rich) etc. before it died, I'm leaning toward a bad ECU. I do know that it will crank and run with throttle body cleaner sprayed in the throttle body.

 

[Will]

I think you are a long way from calling the computer bad. I would check every ground, every cable in the engine compartment including the battery terminals and cables, every sensor with the tests like are shown in the MECS 3 and MECS 4 files I attached. Computers never fail, though good ones are often replaced. I thought I had a bad computer on my 4.0, replaced it with another used one and the truck did the same thing it was doing. I don't think it's the computer. But that's for you to say.

 

[fix_or_repair_daily]

My dad had a 91 b2600 and when we got it, it was very hard to start. Also when it did start would run very rich and rough. I tried everything I could think of to fix it, but couldn't. We took it to someone and it was the ECM. I read several places online that they were very failure prone.
My $.02
Josh

 

[fire239]

Yea, from all I can find out the 90-93 or so ECU are VERY prone to failure. It is due to them being manufactured in those years with defective capacitors. The ones that were used would get hot and leak fluid onto the board. This is sometimes obvious by looking at the board and sometimes not so obvious. The rate of failure is also dependent on the heat and humidity where you live. I live in the deep south so I have plenty of both. I think I will try a different ECU and go from there.

Thanks

 

[Will]

My truck spent the good years in Iowa where 90 is hot and the humidity is what's kicking your butt.

 

[locknar]

not sure if the B2600 is wired different than the B2200, but the fuel pump relay was behind drivers side kickboard, it was labelled a b c d and by jumpering two together you could run the fuel pump independently. If it is there I can go look up the pin outputs for testing

 

[fire239]

The relay is behind the drivers side kickpanel. If there is something there I can try, I would be glad to hear it. I did jumper the fuel pump test connector in the engine compartment that is beside the fuel filter, but this failed to energize the pump.

 

[locknar]

You can test the ECU before replacing it, with a digital volt-ohmmeter, by checking the voltages on terminal located just below the steering column.

But for the fuel pump--The ECU turns on the fuel pump relay based on inputs from the ignition switch and the coil,
After the engine starts the ECU runs the fuel pump from the Relay ground.

To Test
1) check voltage D to ground, turn ignition on, should measure 12volts
2) ignition off, jumper B to D on the relay behind the kickpanel
ignition on, fuel should start running,
3) ignition on- measure 12 volts on A t D only
if not -check ignition + power feed
4) Allow engine to idle-- measure 12 volts on AB, and D if B does not read
replace fuel pump control unit
if no voltage A D, check coil and its power

if these test then it could be the ECU not sending the ground signal to the relay.

 

[fire239]

Thanks for the info. I'll look at this tomorrow.....

 

[coachtdc]

b2600i hesitation hard starting

Did you find out what the problem was,I have a 93 that I had the ecm rebuilt on it ran better for about 10 minutes and now I'm back to the same old

 

[locknar]

there is an ignition module underneath the distributor that wears/fails overtime. When it fails you will get intermittent spark, which once the ignition cuts out the ECM shuts off the fuel pump. Typically you will start to get short runs out of it, and revving the engine higher helps, you will have no idle.
To test remove it and measure across the two terminals with an ohm meter, should read be 900-1200ohms if not replace.