Gmc 7000 no one can fix

As some of you may know, I live on a small dairy that pasteurizes our own milk and delivers it on a home delivery route. Dad does all our delivery, with a gmc 7000 that we built and put a former schwans refrigeration unit on. The engine is stock the way it came from where we bought it. It is a 1989 with a fuel injected 366. It is running rich and runs horribly. We assumed temp sensor and changed it to no avail. Being as we needed it to deliver we took it to the local big truck repair shop. They changed many things including the temp sensor map sensor and other sensors. He determined it needed a fuel regulator which he could not find. We brought it back home and sent the throttle body off to be rebuilt in florida. 1100 dollars later between the two places and it still runs so bad it can't be driven. We need to deliver milk yesterday, what could be wrong? For the money we have thrown at it dad is angry since. A it isn't fixed and B for what we spent we could of bought a used engine and stuck it in there. I can ask him details to help diagnose better. I'm great with diesel engines, gas not so much.
Thanks!

What trouble codes is it throwing?

(If you threw that sort of money at it without knowing, I just don't know what to say.)

Those early fuel injections systems where not that good. Also there are getting to be a lot of the parts not available for them. Plus there are few guys that really know how to work on them.

You can find a regular/carburetor manifold for a GM 366 very easily. Then you can put a carburetor on the motor. You can at least keep it running.

I would be looking for a diesel truck to replace that 366 gas motor. The total operating cost is much less on a diesel in a heavy duty truck.

That's about what happened to my GMC pick up. It is an 87 with throttle body. It didn't through any codes, just run so rich it would flood out. I changed sensors, and screwed with it until I went and bought a intake, carburetor, and distributor for it. Now it runs good.

Yes, while those systems are a bit quirky, they normally DO run quite a bit better than what the OP is dealing with, and, likely the problem is simple.

If a "shop" has been working on it without knowing what is irritating the 'puter, that is NOT a good thing.

Yes I agree with the carb idea we already thought about going that route and wanted to buy a diesel but were putting it off till the money was there for an upgrade. And we don't have a code reader, the shop that worked on it did. I don't know what code it could be throwing.

Guy was on the right track with the regulator; change the oil....it's full of fuel.

What codes are you getting?

Allan

Bought a new 1989 Chevy C-70. Run good for the first ten years, then the trouble started. Local dealer I bought it from told me they didn't work on big truck. Topeka Chevy didn't either. Bought 300 dollars worth of repair manuals and my friend fixed it. Gounding was the problem. Computer had shut clean down. I guess I should sell them manuals, don't have the truck anymore.

I don't have a code reader so I don't know the code. I think it may be on the receipt from work done at shop. I should upload a picture tomorrow it has a list of everything he diagnosed and changed. Allan, how does fuel get in oil? And the voltage regulator you think? Is there a way to test it? I also have been having a hard time getting to get someone to work on it. At least I didn't buy it new I guess!
Thanks
Zach

Those are actually pretty simple systems. I am kind of with Allen here. Sounds like the fuel pressure regulator shot craps. If the throttle body has been done that eliminates the injectors leaving fuel pressure regulator. Pull the vacuum line off of the fuel pressure regulator and if it is wet and full of fuel there's your problem. There should be no fuel in that line. When the diaphragm goes in the regulator the manifold vacuum just sucks fuel through the vacuum line and they run super rich if you can even keep them running. And yes do change the oil. I bet if you pull the dip stick it shows over full due to fuel in the oil.

Greg

Maybe sounding dumb here... Where exactly is the fuel regulator located? I was under the impression that the regulator would of been changed when the throttle body was redone? Maybe I don't know what I'm talking about. Dad pulled it and reinstalled it, I'll have to look under the hood in the morning and read your message again to get a good idea of where those lines are.

Doesn't a 1989 have the regulator in the throttle body? If it cost 1100 bucks to rebuild it I'd of thought they would of put one in or somebody got a screwin.

Not voltage regulator, Fuel Pressure regulator. It literally controls the fuel pressure in the fuel injection system to assure the correct mixture. It is a diaphragm with fuel on one side, and vacuum (from the engine intake) on the other. A pinhole in this diaphragm will leak fuel directly into the intake. It is a common issue. Jim

I have friend who had an early GM TBI pickup that was giving him fits he swapped out the entire fuel system from a wrecked one I had to no avail, he then changed out the distributor and that cured the problem, his was worn out. This was several years ago, and I have slept since then, but it seems like running rich and stalling were his symptoms.

Does an old dog like that have a egr valve on the intake manifold, one of them stuck open and it will run rotten if at all.

I may have miss led you here. Here is where it is located.

It is in the throttle body. I did the one in my 92 C70 with a 366 a year ago. The whole throttle body kit was only $100 or so and took an afternoon to do. It is just a bigger version of the one in a Pickup, with a governor on it.

Check out Item 12.

Trying again.

Thanks for all the help I'll mess with it tomorrow morning and check back in with you then. Again thanks for all the replies!

It is in the throttle body. My bad.

Greg

I could be totally off here, but that looks like a system I had on a smaller vehicle. Does it have a fuel pump in the tank? On mine the fuel pump could not keep up the necessary pressure, and the computer would continually be overcompensating, and then undercompensating. but surely someone has already done a pressure test. Good Luck

Find out what codes it's throwing before spending any more money! If there are no codes it's the computer itself. Most of those older systems will not throw codes when the computer is bad or not functioning correctly because of grounding issues. If it's throwing multiple codes do a little research. Sometimes one sensor or bad part can make other sensors read bad.

Rick

Being the truck is a 89, it should run OBD 1 codes. I know smaller cars/trucks are different from larger, but with OBD 1 there was a way to retrieve codes WITHOUT a code reader/scanner, but I can't remember how now. You would go through a process and count blinks of the "service engine light" if I recall correctly.. OBD 2 which requires the scan tool came in in like 94 or 95 if I'm not mistaken.

Maybe someone else here can tell you how to do it without the reader?? (I'm just a pinch too young to remember how my dad used to do it on our family's early 90's Chevy cars/trucks, and all of my vehicles have either been long before OBD1 or have been new enough to have OBD2)

Brad

Jim and Greg and Allan... the TBI fuel pressure regulator is NOT connected to manifold vacuum like the port injected units are because the injectors discharge ABOVE the throttle plates, into more or less atmospheric pressure vs. the port units that discharge into manifold vacuum so no vacuum compensation is needed.

On these TBI units, if the diaphragm fails, fuel will spill on top of or through the air cleaner mounting flange.

We had 1 366 FI in the fleet back when I worked there, It used to crud up the dist cap and rotor all the time and SOME ONE WAS ALWAYS PUTTING DIESEL FUEL IN IT!!!!! Maybe check and see whats in it for fuel, just an idea. Is the exhaust free!!

Zach:

Reading OBD 1 Codes WITHOUT an OBD Reader.

https://www.youtube.com/watch?v=UIKdbTFvyUU
OBD 1 Codes without a Reader

One guy says it is the throttle body (that you just paid to fix). Another says it is the distributor. Yet another says it is the EGR.
HOLD ON!!!!!

Pulling codes might tell you something. However, the older OBD1 systems were a lot less complicated than the newer systems, and a lot less sensitive. Getting a bit of understanding about the system will help considerably. As you can see, the "shotgun approach" is expensive and ineffective. You already spent a small fortune, and it is still not working right.

The system is basically a feedback system. The main important components are the OXYGEN SENSOR, the MAP SENSOR, and the INJECTOR BODY.

The injector body (throttle body) contains the injectors, throttle position sensor, and fuel pressure regulator. If it has been rebuilt and verified, it is likely NOT the problem. That can be verified by checking the fuel pressure and observing the injectors. The fuel feed can be observed from above. It should look like a fine mist coming from each injector in a fan shaped pattern. No droplets or drips.

A bad OXYGEN SENSOR can cause the engine to run rough and rich. The system is a "feedback" system. The primary mixture control is feedback from the O2 sensor to the CPU. MAP sensor (that has been replaced) is secondary, and is more important in open loop than in closed loop operation.

A worn distributor shaft will usually result in rough running to a no start condition depending on the amount of wear. This is a condition that would come on progressively over a period of time.

All things considered, I would discount the "short answers" given by some because there is NO SHORT ANSWER. If it was the same problem each time, there would be no need for repair shops or mechanics.

Sadly, I have a few tools that might help you out. I have several older OBD1 scan tools that allow you to read sensors "live" on GM products. If you are still stuck, maybe I can send one to you. I no longer use or need them.

jimg is correct.. In that the shotgun approach is expensive and ineffective as you have now found out. The other approach of buying a carb, intake, and distributor can also be troublesome and ineffective if not done correctly, and really does not address the issue, and keep in mind that if you simply put a carb and distributor on, other systems may come into play and need dealt with such as fuel pump, or other systems that are controlled via ECM. As jimg said, these are really simple systems, but few people really understand them, thus the tendency to just start throwing sensors, egr valves, etc at them, leading to hundreds of $$ wasted, and not addressing the issue. I wish I had $1 for every time I have heard the term "it's probably just a sensor". Most times they have no basis, but since they do not know how the system actually works, they assume the unknown. But, I have seen that same approach with old carburetor based systems as well where folks would rebuild a carb, plug wires, points, etc and still not help the issue ultimately finding something like a bad vacuum hose, fuel pump, or any number of things. Find out what codes are stored, if any, and determine items that can be eliminated based on what has been already replaced, and post what you know and someone will likely be able to help. Don't get me wrong, I have made the same expensive mistake of throwing parts at them in the past, and it is very easy to start down that path.

Check all computer ground wires. Also I would take a fuel sample and look for contamination.