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Engine rebuild and harness swap. Does not stay running and runs rough

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Old 07-07-2012, 05:38 PM
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Car: 1989 Pontiac GTA/2007 TrailblazerSS
Engine: 350 L98/LS2
Transmission: 700-R4/4L70E
Axle/Gears: 3.27/4.10
Engine rebuild and harness swap. Does not stay running and runs rough

Last year i removed my 350 and replaced most of the gaskets and seals. i did not dig too far as to remove the heads or cam/crank and pistons. just the basic gaskets.

i also removed my old wiring harness because it had been so hacked that i had starting/power issues and i just installed a new/used one. which looked to be pretty decent.

i'm trying to time the engine now and it won't stay running unless i open the throttle a little bit. and then it seems to run rough and pop through the intake.

i'm pretty positive i have the distributor in correctly, and i disconnected that timing connector. pretty positive i have all the sensors plugged in, and triple checked my plug wires.

no engine light is on, but it does work..

any ideas?
Old 07-08-2012, 01:35 AM
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Car: 1989 Pontiac GTA/2007 TrailblazerSS
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Re: Engine rebuild and harness swap. Does not stay running and runs rough

cmon, anyone?

i gotta get this thing going, and it's been fighting and fighting me.
Old 07-08-2012, 08:11 AM
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Re: Engine rebuild and harness swap. Does not stay running and runs rough

Is this a TPI setup? If so, the lack of idle could be your TPS. Do a search on this site. There is an excellent step by step on how to adjust it.
Old 07-08-2012, 11:55 AM
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Re: Engine rebuild and harness swap. Does not stay running and runs rough

Yep this is tpi. Would a bad tps cause it to run rough as well? And pop through the intake?
Old 07-08-2012, 12:18 PM
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Re: Engine rebuild and harness swap. Does not stay running and runs rough

Originally Posted by blackbeauty89
Yep this is tpi. Would a bad tps cause it to run rough as well? And pop through the intake?

Not likely. I'm just trying to address one issue at a time. What is your fuel pressure? It should be around 42-43 at the rail.
Old 07-08-2012, 02:28 PM
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Re: Engine rebuild and harness swap. Does not stay running and runs rough

I tried something today. Unplugged my MAF to see if that made a difference, and it fired up and idled. Probably around 350-400 rpm still with intake popping. But I plug the MAF back in and it starts then dies right away. The MAF is also new

I don't have a pressure tester but it seems ok. Once I give it a bit of gas it stays running, but not well
Old 07-08-2012, 03:24 PM
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Car: 1988 IROC-Z Camaro, 1981 Trans Am
Engine: 350 TPI, 301 N/A
Transmission: 700r4, 350thm
Re: Engine rebuild and harness swap. Does not stay running and runs rough

When you unplugged the maf youre putting it in "limp-home" mode, causing it to run richer and on pre-set values stored in the computer, not by what the engine sensors are telling the comp. If you can get it to run long enough like that, i would try to time it like that (if possible, im not 100% sure but i think you can), then plug the maf back in and see what it does then go from there.

Still would help to know the fuel pressure.

How is the IAC? New? If not that may need to be adjusted causing your problem. But a popping thru the intake is usually a sign of wrong timing
Old 07-08-2012, 04:58 PM
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Re: Engine rebuild and harness swap. Does not stay running and runs rough

Well I just rechecked the timing and I don't even see the mark when it lights up. Had a buddy help me yesterday and guess he really messed it up
Old 07-09-2012, 08:36 PM
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Re: Engine rebuild and harness swap. Does not stay running and runs rough

now the timing is very close to 6 and it still runs like ****..

http://www.youtube.com/watch?v=DT4ik...eature=mh_lolz
Old 07-09-2012, 08:47 PM
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Car: 1988 IROC-Z Camaro, 1981 Trans Am
Engine: 350 TPI, 301 N/A
Transmission: 700r4, 350thm
Re: Engine rebuild and harness swap. Does not stay running and runs rough

Lol that does run like poopy.

Without a definite answer for the fuel pressure i would say that would be a good thing to verify, if it checks out ok you will be able to cross that off your check list without worrying about it anymore.

Did you ever plug the est back in?

Have you ohmed your injectors? Tested any other sensors? Hows the IAC valve?

Does it get better or worse under throttle?
Old 07-09-2012, 09:07 PM
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Re: Engine rebuild and harness swap. Does not stay running and runs rough

I did not test injectors or other sensors. I did plug the est back in and it didn't really make a difference.

Once I get it to run and move the throttle a bit it seems to hesitate and then jump to 3 grand. Sometimes I have to keep my foot in the throttle 1/4 to keep it at idle
Old 07-10-2012, 09:56 AM
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Car: 1988 IROC-Z Camaro, 1981 Trans Am
Engine: 350 TPI, 301 N/A
Transmission: 700r4, 350thm
Re: Engine rebuild and harness swap. Does not stay running and runs rough

Id do:

f.p test
ohm injectors
test / adjust tps, iac valve (clean), test knock sensor

I just remembered you said you did a rebuild, have you checked compression of all 8 cyl?
Old 07-10-2012, 10:08 AM
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Axle/Gears: 3.27/4.10
Re: Engine rebuild and harness swap. Does not stay running and runs rough

I didn't do a complete rebuild. Just replaced most of the gaskets and seals except for head gaskets and anything inside.

I also might try and use my old plug wires and see if that helps.
Old 07-10-2012, 08:34 PM
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Re: Engine rebuild and harness swap. Does not stay running and runs rough

Ok pretty sure I have it timed correctly.

Still pops and hardly runs. And the exhaust smell is TERRIBLE. I can't stay in the garage more than a few minutes before my eyes start burning.

I changed my new plug wires to my old ones, timed it to 6*, unplugged the batt to reset the PCM, and checked for codes after hooking the batt back up. No codes showed up before or after I ran it, but after I plugged the batt back in and turned the car to run, I heard what sounded like a relay or something clicking on and off very rapidly. Couldn't quite tell where it was, but it was loudest near the intake plenum, maybe near the EGR.

I'll get another video up of what is going on when I'm in the car making it run
Old 07-10-2012, 08:46 PM
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Re: Engine rebuild and harness swap. Does not stay running and runs rough

are you sure you adjusted the valves correctly, looks like it has factory multi tech's those are junk.
Old 07-10-2012, 08:49 PM
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Re: Engine rebuild and harness swap. Does not stay running and runs rough

never touched the valves.
Old 07-10-2012, 08:57 PM
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Re: Engine rebuild and harness swap. Does not stay running and runs rough

sorry, I misread, Thought you pulled the heads. I would leave the est connected so you will have timing advance. Ohm your injectors if they are multitech's chuck them and call southbayfuel injectors and get there bosch 3's. sounded like a lean miss of timing issue. firing order correct 1,8,4,3,6,5,7,2 in a clock wise rotation ?
Old 07-10-2012, 09:03 PM
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Re: Engine rebuild and harness swap. Does not stay running and runs rough

yep the firing order is correct. checked a lot lol.
Old 07-10-2012, 09:17 PM
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Re: Engine rebuild and harness swap. Does not stay running and runs rough

here's the vid

http://www.youtube.com/watch?v=2a0iB...ature=youtu.be

so like i was saying in the vid, i had to keep my foot 1/4 in the gas, it would idle for a bit then rev up real quick
Old 07-10-2012, 10:17 PM
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Engine: 350 TPI, 301 N/A
Transmission: 700r4, 350thm
Re: Engine rebuild and harness swap. Does not stay running and runs rough

Thats really weird. I have never seen anything like that before to be honest. I could kinda see the injectors as being the problem tho, and it would make sense.

Those multects are junk, and if they are starting to fail it would cause it to run poorly most of the time, then they come back strong for a second and while they come back your foot has the pedal down 1/4 way, so it revs like it does. You follow what im saying? (dont think i worded it very well lol)

Have you checked for vac leaks? I suppose its possible you have a severe vac leak around the intake area. If its possible, spray carb cleaner all around the gaskets that you changed and see if it affects the rpm. If you cant do thi, use a mechanics stethoscope to check, or you can use about 1ft of heater hose to track down leaks (stetho. is better of course)

start by ohming those inj's then posting back with results. In case you dont know, they should all be above 16 and within .5 of each other. If they all pass the ohm test that still doesnt necissarily mean your inj are good, though.
Old 07-10-2012, 10:30 PM
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Re: Engine rebuild and harness swap. Does not stay running and runs rough

hope fully you didnt do one of these
Old 07-10-2012, 10:50 PM
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Re: Engine rebuild and harness swap. Does not stay running and runs rough

lol hopefully not but, it would be an easy fix!
Old 07-10-2012, 10:57 PM
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Re: Engine rebuild and harness swap. Does not stay running and runs rough

Lol! Umm I don't think I did!
Old 07-11-2012, 02:42 PM
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Re: Engine rebuild and harness swap. Does not stay running and runs rough

Lol alright, have you been able to do anything yet? FP, check for vac leaks around intake, ohm inj's?
Old 07-11-2012, 03:12 PM
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Re: Engine rebuild and harness swap. Does not stay running and runs rough

Nope haven't had a chance too. I will after work though.

Gonna check for vac leaks around intake, tps, gonna tap on the iac and see what happens first, ohm injectors, see if I can find a pressure tester
Old 07-11-2012, 07:41 PM
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Re: Engine rebuild and harness swap. Does not stay running and runs rough

Well all my injectors read about 16.5 to 16.6. So those must be good? And I used a stethoscope to listen to my injectors and I can hear em all working

Last edited by blackbeauty89; 07-11-2012 at 08:48 PM.
Old 07-12-2012, 02:35 AM
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Re: Engine rebuild and harness swap. Does not stay running and runs rough

The last set of multitec's I had ohmed them same and worked flawlessly. now on too vacuum leaks.
Old 07-12-2012, 07:20 PM
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Re: Engine rebuild and harness swap. Does not stay running and runs rough

well i sprayed some starting fluid around the intake runners and plenum, and the engine revved up pretty high. think i found the problem then!
Old 07-12-2012, 11:55 PM
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Re: Engine rebuild and harness swap. Does not stay running and runs rough

lol well, thats a good thing i suppose, im sure by now your just ready to get the thing fixed lol. Did you use a tube on the tip to better pin-point the vac leak? Do you think you know where its coming from?
Old 07-13-2012, 12:31 AM
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Re: Engine rebuild and harness swap. Does not stay running and runs rough

Well I found that 1 bolt was loose and another one was just laying on the intake manifold. Also I had the runners switched around.. Oops lol
Old 07-13-2012, 01:06 AM
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Re: Engine rebuild and harness swap. Does not stay running and runs rough

Lmao.... Hows it running now?
Old 07-13-2012, 07:15 AM
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Re: Engine rebuild and harness swap. Does not stay running and runs rough

I ordered a new gasket kit just to be safe lol. And 1 bolt is just missing. So I need to get 1 somewhere. It'll probably be done this weekend and I'll let you know lol
Old 07-13-2012, 08:14 AM
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Re: Engine rebuild and harness swap. Does not stay running and runs rough

well I was going to suggest a big vac leak but you found it. I had a 89 Formula a few years ago that had a lower manifold leak but when I put it back together I broke the hard vac lines that come out of the rear of the plenum. Well the car acted exactly the same. Thats one thing about SD, you can have a vac leak and the car will still run ok.
Old 07-15-2012, 01:50 PM
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Re: Engine rebuild and harness swap. Does not stay running and runs rough

Well my car runs great now. Takes a little bit longer to start than it used to. But once it starts it runs well
Old 07-15-2012, 01:59 PM
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Re: Engine rebuild and harness swap. Does not stay running and runs rough

Old 07-15-2012, 02:18 PM
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Re: Engine rebuild and harness swap. Does not stay running and runs rough

Glad to hear. Hopefully it'll start normal soon lol but what matters is you can drive it again!
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