tbi problems

gbbronco · Jul 5, 2011

I have a yj with a tbi 5.7 and under acceleration it is busting up and shuts off. With the transfer cases in low and under gradual acceleration it runs good. where should I start trying to fix this problem.

gbbronco · Jul 5, 2011

I am running a airtex fuel pump that runs a 12 psi and maxes out at 17. Is this to much pressure. Also could it be the pickup on ths distributor. Moving under hard pressure

doctordick · Jul 5, 2011

Has this setup been running and now acting up or is this a new setup? Stock cam? Fuel pressure 17lbs while running,... too high check for pinched/plugged return line. Will flood when starting if this is the problem. Check for vacuum leaks. Injector plugs switched, red on the right (passenger) side. Swap in another MAP sensor if you have one. Hope this helps, if not, PM me, I can give you pinout voltages if you don't have an OBDII reader.

RBaker · Jul 5, 2011

This setup has been in my jeep for only a couple months. Its a new rig it runs pretty good under load but bust up in high range. What should my fuel pressure be under load.

doctordick · Jul 5, 2011

from 9 to 13 psi. Do you mean it won't pull in high gear range or won't pull at high RPMs?

RBaker · Jul 5, 2011

It will pull in high range but you have to pedal it and spoon feed it until it picks up. Once the rpm gets up it does ok. With the cases in high at a full stop if you go full pedal it will bust up and shut down. With them in low it picks up and takes off.

doctordick · Jul 6, 2011

Sounds like a fuel issue, that said you need to check a couple of basics first. Are both injectors firing? Timing should be 0 degrees with the test connector disconnected ( one pin inline connector, tan wire with black tracer). Check manifold vacuum wih a gauge, should be around 18-20 inches at idle. Check fuel pressure with a gauge as close to the throttle body as you can get. Should be 9-13 psi but a little higher doesn't hurt. If it's above 14, you may have a restricted return line or bad regulator in the throttle body. Below 9 lbs, check filter and pump (good voltage/ground at the pump?) Restrict the inlet line between the gauge and throttle body and run pump. If pressure is below 9 lbs, problem is on the tank side of the gauge, if it is 9 lbs, or above, the regulator in the throttle body is bad. If all checks good, you may want to rebuild your throttle body, there are screens on the injectors that can plug up and o-rings which can leak off pressure. A good kit with a regulator diaphragm is about $30 and it's a very simple job, much easier than a carburetor. Are you sure you have the right injectors? 4.3, 5.0 and 5.7 engines all use the same throttle body, but the injectors have different flow rates . I have not been able to come up with a reliable way to identify them, so i'm assuming this is the throttle body for your engine. TPS check is easy, ign on, not running, check voltage on the dark blue wire. Should read .7v at idle, rotate throttle and voltage should smoothly rise. Map sensor should read about 1.1 volts at warm idle on the light green wire. That all sounds like a lot to do, but probably will only take around an hour and you'll most likely find your problem. If not, post or PM :dblthumb:

MUD MAN · Jul 6, 2011

I'm glad you posted this! I just got done converting my SBC over to a tbi and I'm having the exact same problem. This is some very good info for me but I work on a tow boat so I'm not going to be able to work on mine until the end of the month. If you don't mind would you please post what your findings are so it gives me an idea where to start when I get home. Thanks in advance and I sure do appreciate all the info!

doctordick · Jul 6, 2011

One more simple thing I forgot. Drain or siphon out about a quart of fuel into a clear glass container. Let it sit for a few hours to see if there's water in it. This worthless ass ethanol fuel has a ton of water in it and if your rig sits without running for long periods water will accumulate in the tank. After ruining $200 worth of injectors, I always use Sta-bil. The pintels (the little plunger in the injector) were actually rusted because the water in the fuel had settled in the bottom of the throttle body. Your fuel pump is below the bottom of the tank, right? Airtex pumps blow but they don't suck worth a damn.

MUD MAN · Jul 6, 2011

Also mine will start and idle fine but after a few minutes it just stalls but you can instantly hit the key and it fires right back up?

RBaker · Jul 6, 2011

Yes my fuel pump is below the fuel cell and mounted about a foot from the tank. I am on my second tbi unit but both were used. Tpi sensor is good it is brand new and has been checked. I will work on the motor over the next couple of nights and post what I find.

MUD MAN · Jul 6, 2011

Thanks man :dblthumb:

What part number is your fuel pump?

stump jumper · Jul 9, 2011

man I got the same setup. And had that problem 2 diffrent times. first time it was the darn airtec pump(they suuuuuuuck). The second time it was water in the gas. I have been running the tbi for about five years. Dont get a holley pump either it lasted about 6 months for me and is currently bad. If you guys know of a good fuel pump let me know cause I have went through about five airtechs over the years thanks to the good ole lifetime warranty at orielys and a holley. I would like to buy one that would last longer than a year or so.

doctordick · Jul 10, 2011

After running external pumps for years, I chopped up my fuel cell and installed an OEM in-tank pump. No more problems. Waaay cheaper, quieter and way more reliable.

stump jumper · Jul 10, 2011

Thanks that may be what I do next.

doctordick · Jul 10, 2011

While you're at it, go ahead and permanently install a fuel pressure gauge in the hard line as close to the throttle body as you can. Summit has a 15 lb gauge for about 18 bucks and I think you can get them from O'reilly. You'll be glad you did!!

COLT · Jul 22, 2011

I am having the same problem with mine busting up really bad when I pin it to the floor. if I spoon feed it slowly it will take RPM but that is the only way to get it. I have also noticed that it takes at least 5-6 seconds of turning the motor over before it starts. Could this be some sort of drain back issue I am having with the regulator inside the throttle body? I pulled my fuel filter today and it had all kind of mess inside. I replaced it with another and It ran a lot better but still not 100%, and I still had the starting issues of having to crank the engine for an extended amount of time before it would run. When it is at idle it runs perfect. I only have the busting up issues when I gun it. I will get an OBD2 tester tomorrow and see what I can come up with, but would still love some pointers on the drain back issue while starting. Thanks! COLT

BTW This is a new rig and my first time dealing with TBI chevy style. I have a lot of experience with the FAST ez efi but that is about it.

TOYTOACRAWLERS · Jul 22, 2011

if all u are needing is 13 psi then get a holley blue pump for racing or a mallory comp pump for a carb set up i hve been running a holle blue pump on my street car for 13 years and it has never failed me they are more reliable than the efi stlye pumpsjust my opinion

doctordick · Jul 22, 2011

Colt, you didn't say what kind of pump you're running, but if you're running off the original relay and wiring, the pump should run for about 2 seconds when you turn the key on. If the pump is producing adequate pressure, that should be enough time to pressurize the system. Draining back is not really an issue because fuel is retained in the throttle body, it just needs to be pressurized. Check out the rest of this thread for some troubleshooting tips. If there was a lot of gunk in your filter, your pump may be damaged and not producing enough pressure. Be sure to check your MAP sensor, and look for vacuum leaks. Either one can cause similar symptoms

TOYTOACRAWLERS said:
if all u are needing is 13 psi then get a holley blue pump for racing or a mallory comp pump for a carb set up i hve been running a holle blue pump on my street car for 13 years and it has never failed me they are more reliable than the efi stlye pumpsjust my opinion

I've thought about it but never tried running a Holley blue pump, I'm just not sure if the pulsation of such a high volume pump would cause a problem :dunno:

Stock intank pump is the best I've found.

COLT · Jul 22, 2011

doctordick said:
Colt, you didn't say what kind of pump you're running, but if you're running off the original relay and wiring, the pump should run for about 2 seconds when you turn the key on. If the pump is producing adequate pressure, that should be enough time to pressurize the system. Draining back is not really an issue because fuel is retained in the throttle body, it just needs to be pressurized. Check out the rest of this thread for some troubleshooting tips. If there was a lot of gunk in your filter, your pump may be damaged and not producing enough pressure. Be sure to check your MAP sensor, and look for vacuum leaks. Either one can cause similar symptoms
I've thought about it but never tried running a Holley blue pump, I'm just not sure if the pulsation of such a high volume pump would cause a problem Stock intank pump is the best I've found.

Will check on the map tomorrow. I am running the stock in tank pump. Not sure how the guy before me had it wired though. Thanks! COLT