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Old January 14th, 2013, 02:29 PM   #1
dochereford
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Default 1993 5.7 TBI timing issues

I have a new install into a CJ5.
Idle is good but give it gas under load and it runs like its missing. I can rev it and it sounds great.

Setting the timing, I unplug the brn/blk wire by the dist to disconnect PCM control. the problem is, is that there is no difference; plugged in or not. This tells me that the PCM is not effecting timing for some reason.

I'm going to try and manually advance the time until it knocks and see if my symptoms change.

Any other ideas? I could ring out that wire and make sure there is no breaks. other than that, Im at a loss.

tom
79 CJ5
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Old January 14th, 2013, 02:34 PM   #2
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More info:
No EGR, blocked off
All other sensors good or replaced. (didn't test knock sensor)
No data plug - I haven't wired on into the harness yet.
No vacuum leaks whatsoever.
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Old January 14th, 2013, 04:03 PM   #3
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Motor needs to be over 160* and the computer needs to know it is. So check temp switch.

If you built the harness it could be anything.
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Old January 14th, 2013, 04:28 PM   #4
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Thanks Dave. Motor is operating at temp.
Harness isn't totally custom. Just enough to splice with cj.

I guess I'm wondering if someone has the knowledge of the timing signals the PCM expects so I can troubleshoot it more effectively. I feel I'm almost there but this last 5% of the job is driving me crazy. I'm almost ready to convert to carb. (ouch, I realize what that entails.)
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Old January 14th, 2013, 06:39 PM   #5
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Why is it timing? Sounds like a fuel issue or one injector is fualty. What pump are you using and is there a return line?
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Old January 15th, 2013, 05:54 AM   #6
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check fuel pressure!
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Old January 15th, 2013, 07:30 AM   #7
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Quote:
Originally Posted by dochereford View Post
Thanks Dave. Motor is operating at temp.
Harness isn't totally custom. Just enough to splice with cj.

I guess I'm wondering if someone has the knowledge of the timing signals the PCM expects so I can troubleshoot it more effectively. I feel I'm almost there but this last 5% of the job is driving me crazy. I'm almost ready to convert to carb. (ouch, I realize what that entails.)
I just put tbi on mine and had the same type of problems. Under load it would fall on its face at wot and back fire. Put a inline fuel pressure gauge and had 11psi. I found a small leak at the regular so I put a kit in it and ended up at 13 psi.

The other thing was base timing is supposed to be 0* with the wire unpluged but my 350 won't run there it likes 11*. I pulled my hair out over this chasing timing untill I figured out the harmic balancer was bad and the timing mark was moving.
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Old January 15th, 2013, 11:30 AM   #8
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Fuel pressure is at 9psi. No leaks. New Carter electric fuel pump. The spec is 9-15 I believe. Yes I have a return line and the TB has been rebuilt. The injectors have a very nice spray pattern.

Little Dave, did kicking that pressure up solved your problem or was it the timing?
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Old January 15th, 2013, 05:12 PM   #9
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Quote:
Originally Posted by dochereford View Post
Fuel pressure is at 9psi. No leaks. New Carter electric fuel pump. The spec is 9-15 I believe. Yes I have a return line and the TB has been rebuilt. The injectors have a very nice spray pattern.

Little Dave, did kicking that pressure up solved your problem or was it the timing?
Both it ran a lot better but still wasn't right. Then I started with the timing. 9 psi is on the low side unless your motor is stock.

My plugs are still white very little brown on them so I ordered a adjustable regulator and going to try a few more psi and see how she runs.


Little light reading
http://www.cfm-tech.com/gm_tbi_fuel_pressure.htm

Last edited by Little Dave; January 15th, 2013 at 06:22 PM. Reason: Typo
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Old January 18th, 2013, 11:33 AM   #10
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Motor is stock.
My plugs are fouling.
One thing to note and I'm investigating this further today: Idles fine. Under load, it runs very rough. Turned my lights on and my battery went dead. huh?
Okay, if my distributor isn't putting out enough amps, wouldn't that cause my issues? That never occured to me. I have been plagued with my new battery going down but I thought I just had a current leak somewhere and I'd been putting it off....concentrating on my "timing" issue...
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Old January 18th, 2013, 12:16 PM   #11
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not an expert but being low on voltage can affect spark/coil and computer causing trouble with your injectors. it sounds silly but check your plug wires just to be safe 5 and 7 often get put in the wrong spot and will idle ok. hope it helps, it has helped me in the past
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Old January 18th, 2013, 01:44 PM   #12
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Quote:
Originally Posted by rumis1jd View Post
not an expert but being low on voltage can affect spark/coil and computer causing trouble with your injectors. it sounds silly but check your plug wires just to be safe 5 and 7 often get put in the wrong spot and will idle ok. hope it helps, it has helped me in the past
Correct the computer needs a good 12v to do it's job. Make sure the alternator is wired correctly and the ignition system/computer get the proper voltage.
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Old April 5th, 2013, 09:42 PM   #13
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Update: turns out ECU was bad. Sent it out to be checked because I was tired of chasing my tail. Waiting for the mailman now. I keep ya posted.
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