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Old 01-22-2008, 08:19 PM   #1 (permalink)
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Tbi engine problem

I installed an 87' factory tbi on an older motor and am having trouble. The motor starts and runs, but occasionally tries to stall, probably every 15 seconds or so. It also dies when you put it into gear.Idle seems fine at about 800rpm, i even turned it up to about 1200 to see if that would help, but it doesn't. I've replaced plugs, wires, cap and rotor. I also replace throttle body with another used unit and it helped, but not completely correct. fuel pressure is at 12psi. IAC seems to be working properly. I checked for vacumn leaks and tried another used MAP sensor and IAC. Nothing seems to help. I'm getting pretty desperate. Engine shows no codes and no check engine light. I retrofitted a factory harness for the wiring, any chance i missed one?
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Old 01-22-2008, 09:12 PM   #2 (permalink)
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Did you use an adaptor to fit the throttle body to a q-jet manifold? If you did, sometimes the gasket will slip at the corners where the secondaries enlarge and create a vac leak. Other times the computor has to 'relearn' . You may have also missed a ground wire somewhere.
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Old 01-22-2008, 09:50 PM   #3 (permalink)
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no adapter, i modified a stock intake onto the old heads. possible ground(but possible anything else also) I have been over wires numerous times.
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Old 01-23-2008, 10:48 AM   #4 (permalink)
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My stock setup did that and I changed the elbow on the back of the throttle body and it helped and then I changed the PCM and that did it. Just a thought.
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Old 01-23-2008, 09:10 PM   #5 (permalink)
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i tried a different used dist. and coil with no improvement. amazingly enough, i had a 4.3 computer so i thought what the hell and tried it. It idles good and stays running in gear, but still dies when in gear and steering pump under load. so that has me thinking computer, i have a buddy with several used ecm's, so thats my next move. any other suggestions are greatly appreciated
I also tried replacing the vacumn line on map sensor in case it leaked, no help
I did however get to try out my new fire extinguisher, motor backfired with a little fuel on intake and poof

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Old 01-23-2008, 09:42 PM   #6 (permalink)
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Hmmm it starts up and all but dies...

Well TBI dont like any specs off the stock computer, I'm sure you know that. The thing is that once it warms up it should run off the o2 sensor and reconfigure your tables and run for your setup.

Try letting the truck warm up for a good 15mins if you havent already. My truck is an LO5 with 1.5 rockers and a mild cam and it likes to stall easy when its not on the o2 sensor.

I'd definatly start with that o2 sensor, ya did hook one up right?
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Old 01-24-2008, 11:54 AM   #7 (permalink)
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I do have an O2 sensor, but that is the only sensor i haven' tried a different one of, the motor does idle now, but dies when you put it in gear or if you put a load on the power steering pump. it helped with the 4.3 computer, but still dies in gear with the pump under load. will be trying a new computer this weekend, and now an O2 sensor. It does seem to run better once it is warmed up though.
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Old 01-24-2008, 04:29 PM   #8 (permalink)
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Yeah sounds like a beat o2 or possible a bad ground along the way.
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Old 01-24-2008, 07:19 PM   #9 (permalink)
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I would say unless you have a buddy with free parts to swap...save your money and do a little more trouble shooting.

I don't remember seeing fuel pressures on inlet and return.
No mention of "key on" and "eng running" voltage checks.
Initial set procedures performed.
IAC function verified.

And you can pull the O2 sensor and throw it away if the chip is tuned for the motor..or close.
It only allows the ECM to fine tune the fuel.
If it doesn't run right cold then it's not right and it's not the O2.

Some of your symptoms sounds like there is no timing control.
If the timing stays the same till 2000 rpm and then jumps 20* then the ecm is not recieving the timing signal or the EST is not responding.
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Old 01-24-2008, 08:11 PM   #10 (permalink)
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Quote:
Originally Posted by Bill usn-1 View Post
I would say unless you have a buddy with free parts to swap...save your money and do a little more trouble shooting.


If it doesn't run right cold then it's not right and it's not the O2.
My thoughts exactly!

The O2 reading is not used by the ecm in open loop. (when cold)Its definately not an o2 sensor problem.

Follow the link in Billusn1's signature, read the stickys at the top of the forum page.............here..The Binder Bulletin"]http://www.binderbulletin.org/forums/forumdisplay.php?f=75"]The Binder Bulletin.............Take some time and read the fuel injection FAQ
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Old 01-25-2008, 06:07 AM   #11 (permalink)
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I'm not spending any money diagnosing, i have another tbi engine that ran fine that i've been using parts off of for trial and error. i dont know much about fuel injection so im learning as i go. i keep getting input for possible problems on almost every sensor among other things, so it's hard for me to know whats true and whats not. I will be looking into Bill usn-1"s info, you seem to have a lot of info on all the other tbi posts i've looked into. thanks for current help. Also fuel inlet pressure is 12psi, didnt check outlet, and the IAC seems to be functioning, i took it out and left the wires hooked up and put another in the throttle body so it didnt rev way up, and the plunger moved in and out with revving, does that sound like proper function? dont know another way to test

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Old 01-25-2008, 06:27 AM   #12 (permalink)
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The idle must bevery weak if the power steering pump can kill it from 800 rpm. I would be looking at air/fuel mixture and timing at idle. You mentioned a backfire through the tb, usually caused by retarded timing, lean condition, and or spark being delivered to the wrong place(cylinder) at the wrong time. The first two things that come to my mind are retarded timing or a vacum leak.

The fact that it runs better when its warm re-enforces the lean condition. It also illistrates that the O2 sensor is probably working and ecm is trying to correct a lean condition. good luck.
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Old 01-25-2008, 08:36 PM   #13 (permalink)
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What cam do you have in it? stock or a computer cam
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Old 01-26-2008, 07:27 AM   #14 (permalink)
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cam is a non computer RVcam, motor when originally built had a holley pro-jection tbi on it, was never intended for stock tbi. as far as timing, i've been tinkering with that from the beginning, it only backfires when i'm trying to find the sweet spot. to this point it hasn't idled good enough to put a light on it. the exhaust burns your eyes, so dont think its lean, checked all wires numerous times and also checked for vacuum leaks numerous times. i did pull the buggy out of the garage last night and drove it. it ran like shit at first, sputtering and no power, but after about five minutes it started running great, and when i stopped it was idliing at about 2100 rpm(Probably because i had turned the idle way up to keep it running)Do you think the computer finally figured out how to make it run correct?
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Old 01-26-2008, 09:09 AM   #15 (permalink)
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can anyone tell me the key on and engine running voltage checks, i cant seem to pull up these off the binder bulletin for some reason
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Old 01-26-2008, 09:58 AM   #16 (permalink)
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it sure sounds like a vacuum leak
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Old 01-26-2008, 10:05 AM   #17 (permalink)
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You need to go back and read the wiring FAQ along with some of the others.
The wiring diagrams are posted.
Sheet 1 list all the voltage checks in the outer columns.

If you own a lap top then you really should read the data logging FAQ so you actually know what your motor is doing.

You can guess all day long and lots of people will give you there best guess of what happened to them..but each problem is different.

9 out of 10 problems I deal with are from installation errors and not the system itself.
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Old 01-26-2008, 10:21 AM   #18 (permalink)
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Quote:
Originally Posted by Bill usn-1 View Post
You need to go back and read the wiring FAQ along with some of the others.
The wiring diagrams are posted.
Sheet 1 list all the voltage checks in the outer columns.

If you own a lap top then you really should read the data logging FAQ so you actually know what your motor is doing.

You can guess all day long and lots of people will give you there best guess of what happened to them..but each problem is different.

9 out of 10 problems I deal with are from installation errors and not the system itself.
Bill,

Ive been reading a little of your info on these swaps, and I may have to convince myself to reinstall the stock tb back onto my 87 chevy dd pickup. I could spend a week reading all this info... thanks for your documentation of it. It looks like you have a huge amount of time invested in it.

rarely do we get a chance to dig through that kind of stuff for free.

Thanks for the documentation and your willingness to help.
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Old 01-26-2008, 10:24 AM   #19 (permalink)
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I wasnt saying that the o2 sensor being broken will solve it when its cold. Only once it warms up. My truck runs the exact same way. Stock chip and a cam and rockers and the tables are "off" to say the least. Once the o2 sensor kicks in it runs like it has a chip burnt to my specs.
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Old 01-26-2008, 10:26 AM   #20 (permalink)
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tbi thoughts

my 4.3 was acting op the same way, I solved it by going frim a 15 pound fuel pump to a 45 pound, looking after some tbi setups from gm needed the larger volume of fuel. Good luck

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Old 01-26-2008, 01:00 PM   #21 (permalink)
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Quote:
Originally Posted by Grumpy_old_fart View Post
Bill,

Ive been reading a little of your info on these swaps, and I may have to convince myself to reinstall the stock tb back onto my 87 chevy dd pickup. I could spend a week reading all this info... thanks for your documentation of it. It looks like you have a huge amount of time invested in it.

rarely do we get a chance to dig through that kind of stuff for free.

Thanks for the documentation and your willingness to help.
Thanks,
I just try to give back to the community when I can. I am by no means a self proclaimed GURU or Expert. I simply did a lot of research and "search" then documented all I could find...in layman terms.

I'm simply a DIY'r.
I don't own a chevy and really I'm an old ford guy...but the TBI system is very hacked and simple to adapt to almost any motor.
I run it on my V8's, 4cyl minicooper with DIS, and soon to be on my 2 cyl air cooled Fiat.

The system works...if it doesn't..you really messed up!!

Winaldl software and a laptop, a multimeter along with a little knowledge will go a long way in sorting out the system.
BTW...it's all free. as long as you have a laptop and a $6 cable made from parts at radioshack.
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Old 01-26-2008, 01:41 PM   #22 (permalink)
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Did you check the IAC passages on the the throttle body? On those chevy TBIs, that passage will get clogged up with carbon and soot from the egr, and really kill the idle quality.
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Old 01-27-2008, 07:48 PM   #23 (permalink)
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Motor bugs are gone, thanks to Bill usn info, very informative, i learned a lot. I really appreciate the info with out getting flamed, seems like thats what always happens anymore. I followed your initial setup procedures. I also had the 12v constant hooked to a 12v ign, bad mistake, ecm has to relearn everytime. also just driving the rig for a few minutes made it run a lot better, i guess because it didn't have time to calibrate before? thanks again

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Old 01-27-2008, 08:54 PM   #24 (permalink)
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Glad the information helped.
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