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aaaugh 350 TBI fuel problems!!

J

jeffluecke

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I’m having fuel problems with my mom’s K5 Blazer with a 350 TBI and automatic trans. My brother has been driving the Blazer and said it has been starting really rough. Sometimes he has to crank it over 8-10 times before it will start. The first thing I did was check the spark and we had none. I think I’ve replaced most of the ignition on the truck: Pick-up coil, Module, Coil, Cap, Rotor, Wires, and Plugs. It seems like we have really good spark now, however now the truck will start for maybe 2-3 seconds and shut off. When we key the ignition without cranking, the fuel pump will come on for a couple seconds and shut-off, I think this is normal but would like confirmation. It looks like we are only getting a couple dibbles of fuel out of the injectors. Also when we checked the harness side of the fuel pump connection the test light seemed really dim. Because the filter looks original (????) my plan of action is to replace it first. The questions I have are:

1) If the filter doesn’t solve the problem what is the best way to check fuel line pressure. A friend of mine who is a mustang guy says their injection systems have a Schrader valve that he mounts a pressure gauge directly to, I couldn’t find a similar valve on my line, is there one and where would I find it??
2) I understand the fuel pump relay is on the passenger side firewall directly above the passenger side intake manifold, is this true and what is the best way to check it?
3) What is the best way to check the fuel pump without dropping the tank? I would assume checking line pressure and checking power to the pump, can I run power directly from the battery to the fuel pump to bypass any relays for trouble shooting purposes only?
4) Does anybody know where I can find comprehensive information on how this TBI system works and what components are involved? I’ve got a 78 Jeep CJ-5 with a 350 and a Quadrajet and would like to consider some sort of injection system, but obviously don’t know much about them. Also traditionally when my mom’s blazer was running it would run a little rough and maybe even surge a little when it is cold. From the research I’ve done it sounds like this could be caused by a variety of sensors and a variety of reasons. Would just like to get her truck running tip top!
5) Any suggestions on what else to check would be greatly appreciated!

Sorry for the long post and thanks in advance for your help!
 
first off, welcome to the board. There is a lot of great info (and people) here.

now:
1: Mustangs have a schrader valve, TBI's do not
2: relay is on pass side firewall above pass side valve cover
3: you HAVE to drop the tank to get to the fuel pump
4: comprehensive guide? I too am looking for this /forums/images/graemlins/blush.gif

Someone else who knows more will chime in...just wanted to get ya started. Good luck.
 
Thanks for the input, I've found a pretty good comprehensive guide at http://www.goingfaster.com/spo/tbi.html
Still not comfortable with diagnostics, would still like input on best way to verify fuel pressure, fuel pump and relay troubleshooting.
Also does anyone know how the ECM controls ignition timing. I would have to assume somewhere on the distributor. I didn't recognize any components that would do this when I was replacing the pick-up coil on the bottom of the distributor. Lastly, is there anything else I need to worry about, other than putting the distributor back in the same location with the rotor pointing the same direction when re-installing the distributor???
Thanks
 
is the ses light on. if so get codes first. definatly change fuel filter. also if once its running if you get a decent spray pattern out of the injectors try cleaning the Idle air control valve. ref. www.thirdgen.org for instructions. Do NOT use carb cleaner on IAC. TBI are usually full of crud and carbon after thousands of miles and need cleaned.
 
Pump won't prime the system (running for 2-3 seconds when key is turned to "run") if the relay has failed.

Hard starting is one of the symptoms of a failed fuel pump relay, the "backup" to the relay is the oil pressure switch, which needs to see about 5psi before it forces the pump to run. So after cranking a bit, even with a failed relay it will work. There is a test for the fuel pump relay, I've seen others post it, but can't recall the procedure.
 
To test the relay you should be able to hear it click on and off, just have someone turn the key on (don't start it) and listen for it. You should be able to hear the fuel pump also, if your close to the tank. You can run power directly to the fuel pump without hurting things. Also check your ground wire. For a fuel pressure gauge go hear CFM Tech There is also some good information there too. You might also want to try having the injectors cleaned by a shop that does it, I don't think the stuff in the bottle does much.
 
If after replacing the fuel filter you still have a problem. Check the oil pressure switch in the back of the block by the dist. If the switch is bad the truck will start. After a few seconds if the ECM sees no signal from the switch it shuts off fuel relay. Stopping engine to avoid damage.
 
Finally got the truck started again but raised more questions than answers. As I stated earlier this is mom's truck and my little brother has been driving it so I wasn't fully aware of the symptoms. Today I changed out the fuel filter and the fuel pump relay with no initial change. After replacing both I tried cranking over the engine with no hint of it trying to start. I pulled a plug wire and checked spark against the AC Bracket. I was working alone so couldn't get really close to the wire, but it sure didn't look like it was getting any spark. Next I pulled the plug out of the head and plugged it into the wire. This time I could see spark and the engine tried to fire. After a couple tries I could get the engine to fire for a couple seconds. I put the plug and wire back where they belong and tried cranking again. I could get the truck to run for a few seconds on the first 4-5 tries. I noticed with each new try the truck would run a little longer and with some manipulation of the fuel pedal I could extend the length of time it ran. Each time I tried to start the truck I could get a little longer running time out of it until after about 25 times it stayed running. I left the truck warm up and drove it around the parking lot where it was previously stranded. 50% of the time the truck wants to stall in gear, but after it is warm it will start right back up. Another thing that changes when the truck is warm and shut off is when you key the ignition the fuel pump noise is much more noticeable than when it is cold and will not start?!?!?!? Even after the truck is warm it will not idle smoothly, it wants to surge up and down noticably and is a little choppy, however it has great power when you step on the gas. A couple things I have not mentioned are that the engine light never comes on after it is running, the temperature gauge never seemed to move (I think this is an independent sensor not affected by the ECM), The exhaust has a healthy leak past the Cat, I have replaced the plugs, wires, cap, rotor, module, pick-up coil, coil, fuel filter, and fuel pump relay. The next logical step for me is to replace the coolant temp relay, however the guy at the local parts store said he had a similar problem on his S10 and it was the computer. Any help is greatly appreciated, this thing is driving me nuts!!!!! Am I just thowing more unnecessary money at this thing by replacing the coolant sensor????? /forums/images/graemlins/ears.gif
 
Got a laptop, or access to one?

Go get winaldl, and build the 160 baud cable, and you can make sure the CTS is working right, along with most everything else.

Throwing money at it is obviously not working for you, same as most other people that try that approach.
 
I do have a laptop but am not familiar with the winald or buidling the baud cable. Can someone fill me in a little more on where I would get the software with some instructions and where/how I get the cable. Sounds great for me to be able to trouble shoot via laptop.
Any one else had similar problems with their TBI???
Please keep it coming!
 
You got typical Idle air control valve being stuck symptoms. Try this, take off aircleaner and crank engine while looking at the injectors. I ususally stand in the driver side and watch. You are looking for the spray from the injectors. If you have spray pattern then follow next step. Hold gas pedal to floor sending the ecm into flood mode and see if it will start, it will be flooded so expect bunch of smoke. If it runs I bet you money its the IAC. You would be wise to take the tbi off and clean it really well and all its passages. You can clean the IAC but I recommend a new one. Make sure to clean out the passages where the pvc goes and the IAC pintel rests in the tbi. also get a new tbi to manifold gasket.
 
After reading all of this, I am suspecting either the IAC valve or the oil pressure switch.
 
Thanks you guys again for your help, I'm not thinking the oil pressure switch because after a while the truck started. I'm not that familiar with the IAC switch so I don't know. I think I will pull the TBI off and give it a good cleaning. I read in another post not to clean it with carb cleaner?????? I can't think of a reason this would matter, can I get a little feed back on this. Also have many of you had experience with the winaldl software that was posted earlier. I'm thinking of trying that out, but it would be the first time I've ever done anything like that. Looks like the cable is a little tricky to build!, I've got some EE buddies looking at it to help me build. How easy is this software to use and will it be obvious once it is hooked up to tell whick sensors need replaced??
Thanks again for all the help.
 
the reason not use carb cleaner on the IAC is that the carb cleaner eats away the windings in the IAC motor. You can pull the IAC out of the TBI and then your free to nuke it with carb cleaner. The IAC can be cleaned also but you have to use fuel injection cleaner. I just opted for a new one from autozone for around 45 dollars. Mine took a dump after i cleaned the tbi with the parts cleaner at work.
 
I've run winaldl. Not a lot of time now to go into it, but the 160 baud cable will work for you, for now, and you can get winaldl *probably* from winaldl.com (no time to check though)

There is much better software out there for free (used to be called tunerpro) but it's more in-depth, does more things, and requires the 8192 cable IIRC.
 
[ QUOTE ]
the reason not use carb cleaner on the IAC is that the carb cleaner eats away the windings in the IAC motor. You can pull the IAC out of the TBI and then your free to nuke it with carb cleaner. The IAC can be cleaned also but you have to use fuel injection cleaner. I just opted for a new one from autozone for around 45 dollars. Mine took a dump after i cleaned the tbi with the parts cleaner at work.

[/ QUOTE ]

What kind of symptoms did your truck have when your IAC went bad??? Also does anyone have advice on which is the best software available to tune my TBI with my laptop and do you recommend building your own cable or purchasing one somewhere? This fuel injection stuff is getting a little less intimidating!
 
You can't tune with just the software. You have to get into doing your own chip burning.

www.thirdgen.org in what I believe is the tech article section, has one on burning proms, by "traxxion". Pretty informative.

Do a lot of reading on that board in the forums relating to the ECM if it interests you. "Mangus" is the username of the guy that made tunerpro (and whatever its replacement now is) which for free, is probably the best program out there that does almost everything.

Haven't built the 8192 cable yet, but I did build the 160 cable. The parts at radio shack cost about $3 if you have an old serial cable laying around, about $10 if you have to buy one, so I hear.

I did nothing fancy like the ones you see online, I cut the wires, and spliced in the resistors/transistors as required, taped it all up so no worries of grounding it out, and soldered parts of a paperclip on the wire leads that go into the ALDL connector to make them stiff enough to last more than a couple of "data gathering sessions".

Doesn't need to be beefy, you won't use it THAT often, and you can't drive like crazy with a laptop sitting on the other seat anyways. /forums/images/graemlins/smile.gif
 
This has my interest as well.
My problem was several over Labor Day weekend I rolled pretty hard. When all was okay to fire up, my buggy was running like crap and died within 5 minutes.
It took 4 hrs to get it running agian. In that time we switched distributers, ESC, coils, and computers with a known running truck in the group. My parts always started his truck and my buggy never started.

When it finnaly did fire up agian it was after we hooked an on board welder up to it to charge the battery for several minutes. It fired right up, no codes nothing.

I have a Howell stand alone TBI harness and chip. Howell seems to think that the battery was low on voltage and was not supplying enough to get the computer to work properly. They say that the computer needs to see 12 volts min. to work. I am completly lost.

We did not switch IAC or anything concerning the fuel side of the program.

We did test power at every device in the system and all had power 11.2 to 11.5 volts.

Any takers???
Thanks
 
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