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tbi troubles

J

jdp

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Location
lynnwood, Washington
hey guys, so i have a 1988 suburban that shaving some issues. so when i start it i have to pump the gas to get it to start, it runs super super rough when its cold and when i am actually driving it sputters and kinda falls on its face when you give it gas and it just seems guttless. but when it warms all the way up it doesnt do it AS much and when i ran my code reader it told me it is running too lean

so in the last month the this is what has been replaced
throttle body
injectors
egr valve
pcv valve
02 sensor
throttle position sensor
fuel filter
all cracked rubber vacuum lines
and ecm unit

what else could it be, kinda lost right now with this
 
Sounds like an ignition problem to me. Replace the cap, rotor and plugs and it should clean up the roughness. That's what I would have done first.


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well i have only had it for a week and ive done the ecm, fuel filter, and 02. the previous owner did the rest just searchin for a fix.
but the plugs and wires are aslo new. i will pull the cap and check it out though.
what would make the code 44 show up though, it says its running lean( left oxygen sensor) could the ignition do that?
 
Not sure on the code, hopefully fordum or another tbi whiz can chime in on that. Have you checked the fuel pressure?


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no i have not been able to do that, i dont have a gauge right now to do so. i did wach the injectors spray though and it looks like they are putting the right amount of fuel in. could i tired fuel pump cause that?
 
A tired pump or a clogged fuel filter could can cause some issues. Check into that filter.


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well the filter is brand new and is put in the right direction, i checked that the moment i got it home. it seems to me that it is something to do with a sensor of somekind that is not telling it to richen the air fuel mixture when it is cold because when it is warm it does not happen as offten but it does lack power.
i could try a temp sensor, but really i cant think of what it could be. im thinking a tired pump or a sensor tripping
 
Really feels like fuel problems to me. Since the filter and injectors have been changed, I suspect the fuel pump or fuel regulator.
You need to try to figure out a way to measure the pressure before you start throwing more parts at it.

The temperature sending unit for the computer might cause a problem, but I'm still thinking fuel pressure.

The fuel pressure regulator is on the back right side where the fuel lines hook up. Its a bypass type regulator, not a restriction type.
If the diaphragm fails, or the spring breaks, it will let too much gas go back to the tank and the injectors will not get enough pressure.

You could try pinching off the return line, rubber part, and see if it runs better. Don't run it long with the line pinched off, and you should be able to pinch it off gradually and see the engine pick up.
 
so if i slowly pinch off the line then it will get more fuel right? so if the regulator is bad will it idle up or just run smoother? how would i be able to test that while driving? cuz it really sputters when actually taking off and not too bad when its in park not under load
 
Thats the problem. It could be done while driving, and probably has been, but it would be rather dangerous.
You would have to lay across the engine somehow while someone drove.

I don't suggest it.
Of course I'm one to talk. I once tied myself up under my jeep and let a friend drive it around a parking lot to find a rattle.

Be smart, learn from my idiocy.

You could try restricting the flow with something like a pair of vice grips and then try it. Just guess at the amount.

But, the best way is to pull the regulator and check it out. It does not seem to be hard.
I would give you suggestions or instructions on how to do it, but I have never even seen one.

I run Fords.

If I keep hanging out here, sooner or later I'm going to have to actually work on one of these darn things.


Hang in here, and someone will chime in and give better instructions. It seems to be pretty simple, lots of folks just take it off and figure it out.
 
haha man that sounds like something me and my buddies would do. give me a 12 pack and i can think of some pretty creative ways to fix things ha
yea it cant be too hard, i just dont know how to test it once its out. thanks alot for the info though im going to work on it in the morning before work and see what happens.

it was kinda funny though cuz i bought this rig for 400 bucks to strip and scrap cuz i was told it was dead and wouldnt run but its super straight. got it home poured some gas in the throttle body and it started right up, a little tinkering and its almost a solid runner ha now i dont know if i want to sell it or drive it
 
Drive it for sure. If the body is good, then you got a good piece of equipment.
Its not a Ford, but its not bad.
Check out some of the absolute pieces of junk that folks here have paid good money for and done wonders with. Sounds like you are ahead of the game.

From what I can tell, its not a complicated device. A diaphragm and a spring with some kind of valve seat.
The more pressure on the diaphragm, the more it opens the valve, I suspect.
 
yea i deffenitly got a hell of a deal on this one, it only has 120,000 miles and just had the 700r4 rebuilt too. cant beat the price of 400 bucks ha

yea soo basically the spring gets tired and lets too much fuel return, therefore resulting in loss of pressure. i guess you could say it works kinda like a radiator cap in a way, in theory
 
120k miles,,, I'd check the fuel pressure. Sounds like the way mine drove when the pump was on it's way out, this was on two different vehicles.

Idled fine, just wouldn't go right, replaced the pump, woke it right up.

Actually it's one of the first things I check now when there is a fuel injection issue, as I had installed a new pump in the Burb not more than a year ago, and had a fuel delivery problem not long after a 2000 mile road trip, dropped the tank again and found the little 3" short piece of hose from the pick-up tube to the pump had a small slit in it. Not sure how it got there, but it was enough to let pump pressure out that and not get it to the engine.

Also In both vehicles I had fuel pump issues with, it was always giving me the lean condition code from the O2 sensor.
 
i guess you could say it works kinda like a radiator cap in a way, in theory
Click to expand...

Not a bad analogy.
If you have not done so, check on the adjustment methods for the TV cable on an 700R4. If its adjusted wrong, it will burn up the tranny in a short period of time.
If you are going to keep it, and work on it yourself, you need to buy the membership. But be warned, you will get ideas here that have little relationship with sanity.

I mean, I had my brand new Ford cut in half, shortened to short wheelbase specs, swapped out the transfer case, added a hydraulic pump and tank to run a massive hydraulic PTO winch and put an 8 inch channel iron bumper on it.
I thought I had done a lot.

These guys make me look like an amateur.
Of course, I had started out with a 3/4 ton, I didn't need to put bigger axles on it. These guys jump from a 1/2 ton to a full ton.
 
Time to start back at the beginning... If the previous owner was working on it, double check everything. New parts doesn't mean they are installed properly, adjusted properly, or functioning properly. Second, is this truck completely stock? Recheck every spark plug wire, cap, rotor, etc... Check all the sensor connections, Unplug them and plu them back in. Double check for vacuum leaks, especially at the throttle body base gasket. He put a new throttle body on? Doesn't sound right, because I've only ever seen one as a complete new unit, and they cost more from gm than the truck is worth... If he swapped a used complete throttle body who knows what you have... You say you have to give it gas at startup to get it started, you are actually only giving it more air, the computer controls the fuel by telling the injectors to pulse. You only open the throttle blades an allow more air into the throttle body as well as moving the throttle position sensor. Is you idle air control working, gummed up, and/or set properly? It would seem to me the computer is reading lean, so it's dumping too much fuel and causing you problems, you may actually be running rich. Does it smoke? If so what color is it? Is your CTS (coolant temperature sensor) plugged in? It's the one on te intake manifold near the thermostat housing, not the coolant temperature sensor on the drivers side head. If it's not working it can cause them to dump fuel an not run right. Lot more possibilities, but that shoul get you started. I never trust work done by previous owners!!!
 
TexasSilhouette said:
Classic low fuel pressure symptom.
Click to expand...

Maybe, but the only way to know for sure is to put a guage on it and verify for sure. They've already put a ton of money and parts chasing this, I'd hate to see him waste anymore. Autozone will loan you a test kit for free if you leave a deposit. I once had a brand new spark plug come loose from it's holder under the exhaust manifold that got burnt and would randomly short, it would sometimes not start, run great then terrible, and throw random sensor fault codes that I chased for 2 weeks! I was convinced my wires were good. Then one night it was acting up and I popped the hood and in the dark I could see it arcing... New plug wire and problem solved. Just saying that it doesn't hurt to do the free stuff before he puts any more $$$ into it.
 
That's why I said for him to check the fuel pressure, just sounds like low pressure to me as well, and well, if you have, or can get a pressure gauge or kit loaned/borrowed, it's a free test. I already have a gauge kit due to many fuel pressure problems causing issues on previous vehicles, family or friends vehicles. So it's usually the first place I start when checking for issues that you'd seemingly think to be pressure related.
 
I agree, it's a shame gm didn't put an easy access schraeder valve on thes TBI systems... It'd make checking fuel pressure so much easier!
 
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