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TPI Tuned Port Injection discussion and questions. LB9 and L98 tech, porting, tuning, and bolt-on aftermarket products.

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Old 05-20-2008, 08:29 PM   #1
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Join Date: Oct 2004
Location: Chico, CA
Posts: 539
Car: 89 Firebird, 92 RS
Engine: 2.8L MPFI, 355 TPI
Transmission: t-5, t-5
Axle/Gears: open 3.42, posi 3.42

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Engine problems (major) - Backpressure or internal damage?

-----------------Background----------------------
355 5sp SD TPI 1 3/4" headers, 3" exhaust though single cat, engine has about 30k miles on it

It died/lost power randomly a few weeks back at a stoplight. If I gave it gas it would die, but with some trial and error I was able to stumble the mile home.

The computer shows no codes, no codes in memory, nothing. What is happening right now is it will idle (with occasional hunting [mostly from misses, could be other reasons too]), but if you give it gas it dies.

If you press the pedal down a tiny amount, it will rev up a few hundred to a thousand rpms, any further and it dies (press it to the same location too fast and it dies too). However by working the throttle back and forth in stages it is possible to reach redline (haven't though just in case) or any other rpm. If you stop working the throttle(but keep it pressed) it will return to idle or die (only tried for small values).

There is an exhaust leak from the passenger header somewhere (wasn't there before, at least not constantly), visible at idle. There is a noise (not always, not very loud over the engine/belt noise) coming from the back passenger header/valvecover area, could be the exhauist leak, could be internal topend. It is not injector noise. The noise didn't sound very solid, so I think its the exhaust leak, but I have zero experience with engine noises other than injector clicking, so I have no idea.

I just changed the plugs cap rotor and coil cause they needed it, the store gave me the wrong wires so I have to go back for that (and its possible that some of the old wires are arcing--I swapped out the one I saw that had insulation damage, but they're all pretty old and I didn't pay too much attention to their complete condition.

The oil level was low (and high) at two different points in the past, so top end damage is quite possible, but there aren't any noises to hear (even at 3500+ rpms) other than the noise that is probably the exhaust leak--which disappears amidst the engine/exhaust roar at higher rpms, not what I would expect for internal noise. I couldn't feel any peculiar vibrations from the valve covers either.


--------------------Questions-------------------
Is it necessary (or recommended) to reset timing after changing cap and rotor?

Is there any chance different plugs (they have a different post-thread lenth, went from some bosch plug to the stock delco's) is messing with the tune?

Did my cat blow out, blocking the exhaust, and if it did, would that:
Cause a new exhaust leak (makes sense) ?
Cause a severe (total?) loss of power?
-That is somewhat reversible via throttle play (ie: press down x, lift up slightly less than x, press down x, lift up slightly less than x, etc; this seems plausible if the problem is caused by excessive backpressure, but i have no experience in the matter) ?
Burn oil (exhaust gas reversion plus PCV system or something similar) ?

Also, why isn't my computer throwing any codes?

The last thing I can think of is wiped cam. Does that fit? Would that make any noise? Is there any easy way to check (no garage or jacking area)?


Any and all help is greatly appreciated! Sorry for the essay, I wanted to be thorough (and still feel like I'm missing something). Thank you!
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Old 05-21-2008, 03:07 AM   #2
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Join Date: Oct 2004
Location: Chico, CA
Posts: 539
Car: 89 Firebird, 92 RS
Engine: 2.8L MPFI, 355 TPI
Transmission: t-5, t-5
Axle/Gears: open 3.42, posi 3.42

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Re: Engine problems (major) - Backpressure or internal damage?

bump for great justice
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Old 05-21-2008, 05:21 PM   #3
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Join Date: Oct 2004
Location: Chico, CA
Posts: 539
Car: 89 Firebird, 92 RS
Engine: 2.8L MPFI, 355 TPI
Transmission: t-5, t-5
Axle/Gears: open 3.42, posi 3.42

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Re: Engine problems (major) - Backpressure or internal damage?

not even a single idea?
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Old 05-21-2008, 11:02 PM   #4
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Join Date: Apr 2002
Location: Austin
Posts: 1,295
Car: 82 Z-28
Engine: 383 TPI
Transmission: 700R4

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Re: Engine problems (major) - Backpressure or internal damage?

Sounds like the fuel filter may be clogged.

Remove the fuel filter, pour the fuel out, wipe off the nipple with a clean rag and try blowing thru it in the normal flow direction. You should be able to blow thru it very easily, if not replace it.
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Old 07-23-2009, 05:02 PM   #5
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Join Date: Oct 2004
Location: Chico, CA
Posts: 539
Car: 89 Firebird, 92 RS
Engine: 2.8L MPFI, 355 TPI
Transmission: t-5, t-5
Axle/Gears: open 3.42, posi 3.42

Classifieds Rating: (0)
Send a message via AIM to Naft
Re: Engine problems (major) - Backpressure or internal damage?

figured i'd update for the archives: it turns out the fuel pump was going out, and the black hose replacing the float had a hole in it dumping all the pressure back into the tank.

it will now move under its own power, but it barely idles (and dies after a minute or two), and only after its warm. I couldn't get my y-pipe torqued down with the car on jackstands, so there is an exhaust leak before it atm, i think thats causing my remaining idle problems. Well, I hope. I found a lift I can use only a couple miles away, I just hope I can make it there!
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Old 07-23-2009, 05:02 PM
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