'85 S-10 bad. Fuel pump?

[MarkM66]

I was driving my old '85 S10 (2.5 tbi) to work the other day and the CEL came on, it started to run really rough, and had almost no power.

After awhile the light went off, and it seemed to run fine. But it kept doing this every couple of minutes. It also did this the whole way home.

I'm getting a 44 on the CEL (O2 lean) . OBD1 doesn't tell much.

It'll idle fine, I can't find any vacuum leaks. I pulled the plugs and they're okay. There's no Cat Conv. on it.

My next step was checking the fuel pump. Voltage seems okay, a little under 12 v. key on, little under 14 v. running.

Check pressure. 7psi key on, 8.5-9 psi running. Spec calls for 9-13 psi.

Week fuel pump? Change it?

Anything else I should check before swapping it?

I also checked the fp regulator by blocking the return line. Pressure stayed consistent.

 

[spasm3]

i assume you have changed the fuel filter.

 

[MarkM66]

Filter is not that old.

Fuel pressure was taken before the filter.

 

[beaker60]

Does it have an EGR valve,,that is how the engine will act if it's stuck open,,,even the slightest,,and definately like the other post,,check the fuel filter,,but if your getting 9psi,,with it running,,it sounds like the pump is OK,,now do not qoute me on that,,I've seen pumps do some wierd things.Let me know what you find

 

[spasm3]

i would check it after the filter or just put on another. It might not be the problem, but you would hate to spend a bunch of time and money to discover its a bad filter from the get go.

 

[MarkM66]

Originally Posted By: beaker60
Does it have an EGR valve,,that is how the engine will act if it's stuck open,,,even the slightest,,and definately like the other post,,check the fuel filter,,but if your getting 9psi,,with it running,,it sounds like the pump is OK,,now do not qoute me on that,,I've seen pumps do some wierd things.Let me know what you find


It does have an EGR valve. I'll look into that and get back.

 

[dishdude]

Fuel pump won't turn on a CEL, and usually work properly or competely die. Sounds like something is leaning out the mixture to the point the engine is stalling. MAP sensor?

 

[Merkava_4]

How many oxygen sensors does it have? I'm guessing just one if it doesn't have a catalytic converter...

 

[wander2039]

Try the o2 sensor first. You might want to have a re-sert kit available if it's your only ride. Get a good one aka not a bosch. I think that was the trouble I had with mine all those years. I had to replace the MAP sensor more than a few times and the computer twice.. the egr was always blocked off so that wasn't a issue. All I can say is good luck. I should of pulled the 2.5 and put a 305 in and called it done.

 

[MarkM66]

Originally Posted By: dishdude
Fuel pump won't turn on a CEL, and usually work properly or competely die. Sounds like something is leaning out the mixture to the point the engine is stalling. MAP sensor?


Yeah, but if there's not enough fuel pressure or volume, it could make a lean condition which the O2 sensor would read.

 

[MarkM66]

Originally Posted By: Merkava_4
How many oxygen sensors does it have? I'm guessing just one if it doesn't have a catalytic converter...


Just one, right in the ex. manifold. No cat.

 

[MarkM66]

I put a small inline fuel gauge on it yesterday and went for a drive.

It still runs bad, but after it got warmed up, the pressure only read about 7 psi running.

So if the gauge is correct, that psi reading isn't good.

I think I'll swap the pump. I cut a hole in the bed years ago when I replaced it before, so it's a simple swap. I'm surprised the truck has lasted me this long.

 

[MarkM66]

Originally Posted By: Eric Smith
Try the o2 sensor first. You might want to have a re-sert kit available if it's your only ride. Get a good one aka not a bosch. I think that was the trouble I had with mine all those years. I had to replace the MAP sensor more than a few times and the computer twice.. the egr was always blocked off so that wasn't a issue. All I can say is good luck. I should of pulled the 2.5 and put a 305 in and called it done.


Thanks. What year was yours?

I'll keep this in mind if it doesn't turn out to be a fuel delivery problem.

That sensor is just hanging on the back of the air filter housing, it doesn't seem like it would have much of a function or be that accurate, but I guess it can.

Did you have any issue with blocking the EGR? Did you just make a plate and plug the vacuum outlet on the tb? I keep reading that blocking it can cause pinging.

 

[wander2039]

Mine was a 88. My mom got it for me back in 97 or 98 as punishment for not keeping cars out of the junkyard.. man what a punishment that 2.5/auto couldn't even get out of it's own way. Put it through alot though. Did keep it until 02 or 03 and put 50k. Got it with 100k fresh from a utility company. By far the worst vehicle I've owned even though I put it through alot. Don't remember ever getting good mileage.. a good V8 or V6 would of been an improvement.

Anyways never had a problem blocking the EGR. I did hook it back up for a while but ran the same so I plugged it back up. The MAP sensor should be on the front of the filter housing.. I think anyways been a few years.

 

[mechtech2]

Fuel pump or filter are the first things to check.
If there is crud, a new filter can plug fast.
But the EGR can also cause all sorts of problems, like mentioned.

 

[MarkM66]

I 'think' I have it figured out.

I bought a new Bosch pump for it and installed it. PSI went to almost 12 psi, I thought great. Took it for a drive, went fine for awhile then started running really bad again, got home and psi was down to 6.

Turned it off, waited, turned it back on, 12 psi, so I left it keyed on. And gradually the pressure started to drop.

Listening to the pump/tank, there seemed to be alot of fuel flying around. So with the pump powered, I slowly lifted the sending unit, and there is a piece of rubber hose the connects the pump to the hard line on the sending unit, well fuel was shooting out the side. There was a hole it it.

I replaced that with a new piece of hose. But then the same thing happened

. Pressure started to drop. I looked in there again, and fuel is shooting out of the top of the pump. There a screw hole on top of the pump that fuel is shooting out of now

.

So I'm going to take the pump back to see if there's suppose to be a screw for that hole, or if something popped off there.

 

[MarkM66]

I returned the pump, and explained the issue with the threaded hole. They looked at another one, and it to had that threaded hole.

I'm not sure what it's there for, but fuel definitely came out of it.

I got a more factory fit fuel pump. Going to install that once the snow/rain stops.

 

[mechtech2]

Good diagnosis and good work.

 

[MarkM66]

Thanks.

I got it running, seems to be back to normal.

I guess it didn't really need a new pump, just that hose, but it has one now.