89 K3500 7.4L fuel system thinks full throttle when not.

[hhiibel]

My 89 K3500 tbi 454 dumps fuel like its full throttle.
Very experienced mechanic has replaced the following:
tps, temp sensor, egr valve, fuel pump, plugs, wires, cap, rotor, O2, and module. He says all these tested bad. All this solved it for about 5 days. Then it came back worse than ever. He's still trying to figure it out.

A little history, never had problems like this before. I've been parking outside with hood up in all weather in Northern Colorado for 18 months. Hood is up because of rabbits and mice.

Before repairs the problem was somewhat noticeable and only happened at highway speeds, approx. 1700rpms. Then it seemed to travel into lower speeds. Symptom was slight miss, lack of response, and slight surging. All these things were increasing in noticability. Per mechanic, the problem was the system dumping way to much fuel. After repairs, it was good for about 5 days(150 miles)then one night at highway speeds it came back more pronounced. I reacted by letting up, it got even worse and essentially degraded too full throttle gas at idle. That's the last I drove it. I don't know what the mechanic is seeing now.

The question is with a good tps what would make the fuel system dump to way much fuel? What wires s/b inspected/tested?

When all this started, I got a 24 code - speed sensor.

Also, don't know if this matters, trans was replaced about 6 months ago.

Thanks.

Howard.

[GaryL]

Have you replaced the speed sensor? When you say it is dumping too much fuel, do you mean the engine is racing to 4000 or 5000 RPMs?

[phoebeisis]

Wow, that is a problem.A question.
1)How did your mechanic figure out that the TBI was dumping too much fuel?
I don't know how much memory the ECM on a 1989 has.They didn't have to have full memory/codes until 1996, but obviously you can get codes.Ask him.
I know you said the mech is very experienced, but he is obviously baffled.It seems really unlikely that all those components failed at the same time-impossible in fact.The Throttle position sensor makes sense of course, but the rest-especially the fuel pump-don't really make sense.
If it were me,I would continue with the parts replacing-they are old,and it is worth a shot.
1)The mass air intake sensor -usually somewhere in the airbox or intake snorkle would be my next bet. You don't have an oiled filter-K&N-in there do you? They can kill MAI sometimes.Oh, not sure exactly what the proper term is for the MAI-but it tells your ecm how much air you are taking in per second,so it knows how much fuel to tell the TBI to squirt in.
2)Next bet would be the ECM-the black box.I would try to get a buddy to let you borrow his.It is strictly plug in.Maybe Auto Zone, or Pep boys can test yours and if it is bad,sell you a new one?

I would make sure the mechanic was correct on the original diagnosis.
Good luck,
Charlie

[hhiibel]

Thanks for the replies so far.

It isn't racing to high rpms. The thottle is in the idle position yet dumping full fuel capacity.

Forgot to mention the mps was also replaced. There is no mas.

In the first go around, the mechanic had another guy stop by with a tool for measuring fuel flow at the injector. That's how they determined it was dumping all that it could.

The last thing replaced in the first go around was the fuel pump. I think it had hit the skids after all the full on fuel runs.

The ECM was replaced - I call it the module.

I'm going to have the mech. reset the ECM and see if it goes away and then learns itself back to this bad behavior. I'm thinking this because it was good after the first go around and then the issue came back in spades. Maybe it came back even worse because the new pump can really pour on the gas.

I'm wondering if it all goes back to the code 24 - speed sensor.

The ECM has no playback, and the mech isn't aware of a piggy back device to get a recording.

-howard

[hhiibel]

mech just called.
put on another tps and its fixed.
I pick it up tonight.
fingers crossed.
I'll post an update in a week or so.

-howard.

[phoebeisis]

Wow,that is good news.Let us know how it goes.I can see why your mechanic was baffled.He replaced the item that was the most likely culprit-the throttle position sensor-and it cures the problem, but the problem comes back.I gues he figured-like eveyone else would-that it was extremely unlikely that a new TPI would die in a week.
Good thing he kept pushing,and took a chance on a new TPI.

I have heard more stories of parts-frequently electrical parts which don't even have many/any "moving parts" being DOA or dying waaaaay too soon.I wonder if these are more CS low buck Chinese parts? Many manu use the cheapest bidder for parts.Ask him if he knows who made the part(country, not manu)-many big parts companies contract out parts to overseas companies-usually low buck,crummy Chinese parts.

Luck,
Charlie

[unplugged]

The ECM has no playback, and the mech isn't aware of a piggy back device to get a recording.

Most mechanics won't go to the expense or the time to learn about OBDI data collection and interpretation. You can find out more about it here: obd2allinone.com

[Cableguy]

put on another tps and its fixed.

Well buying a faulty part didn't help any did it.
Good luck tonite!

[84fiero123]

Just a guess but if the injector is dumping fuel, it itself may be the problem, could be getting clogged by crap in the fuel. Problem is injectors are expensive, but they can be cleaned, most mechanics have or at least have access to a pressurized cleaning system for the injectors.

[ChevyTech]

Thse years also had major problems with Cats and distributor shafts. The magnets like to plow up, also oiling of the shaft was a problem.