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People who have done TBI swaps ?

Mudbug1979

Mudbug1979

1/2 ton status
Joined
Aug 4, 2002
Posts
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Location
Monroe,North Carolina
I did a TBI swap about 2 months ago and it ran fine for awhile and here lately it wants to surge only if is in gear. When the truck is in park or neutral it idles fine, I have to idle it up to about a grand in park to keep it from dying in gear. I've checked all of the gaskets for leaks and hoses and I have pulled the IAC out and cleaned it. I have a buddy that has the same system on a caprice and it doesn't seem like mine is putting out as fuel as his is. I'm stumped any help would be greatly apperciated.
 
Do you have a VSS in your system? I wonder if thats not giving you problems... Also, did you use a new fuel pump when you installed the system?

-Dan
 
Yeah I installed a new feul pump and the install was done correctly. I used a Painless Wiring harness and all of the TBI donor parts were factory GM. I installed a new O2 sensor but I did not use a VSS sensor because my Th350 did not come with one. When I installed the harness painless said that my egr valve would not work unless the vss was hooked up. Any Ideas? /forums/images/graemlins/ears.gif
 
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Yeah I installed a new feul pump and the install was done correctly.

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I was talking about the TBI install as a whole.

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I installed a new O2 sensor but I did not use a VSS sensor because my Th350 did not come with one

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Then no, it was not done correctly. I'd suggest browsing www.jagsthatrun.com and www.thirdgen.org forums, learning why VSS is needed.
 
The VSS only helps the egr work and from what I had read the system would run without it, the egr valve would just not function. I was talking about the whole install was done correctly also..
 
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The VSS only helps the egr work and from what I had read the system would run without it, the egr valve would just not function. I was talking about the whole install was done correctly also..

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You've been deceived. Was it painless that told you EGR is all that needs VSS? I'm not gonna go through the whole VSS thing again, it's been covered on any board that has people that know what they are talking about, including this one. /forums/images/graemlins/rolleyes.gif
 
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The VSS only helps the egr work and from what I had read the system would run without it, the egr valve would just not function. I was talking about the whole install was done correctly also..

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Ask BlazzinOR (or whatever his user name is now) what he thought about VSS before he installed it on his 400sbc TPI. He had problems. He added VSS and a proper P/N switch and we had holy wars about it before that. /forums/images/graemlins/thumb.gif

GM didn't put the VSS & switch in there to amuse themselves. The drivability is changed by having one. You think fuel requirements in 4th gear at 3000rpm are the same as 1st gear at 3000rpm? I think this guy needs drug out: /forums/images/graemlins/deal.gif

SECONDLY, Painless harnesses are ganged up on fewer fuses than factory. This makes them harder to troubleshoot electrical problems, and doesn't allow for proper voltage to everything, again affecting drivability.

PAINLESS IS JUNK /forums/images/graemlins/angryfire.gif /forums/images/graemlins/angryfire.gif /forums/images/graemlins/angryfire.gif
DON'T USE IT ON YOUR TRUCK
-Matthew
 
FWIW, and not trying to start anything, I have done four TBI swaps, all using the GM harness, all were put into manual trans vehicles. No VSS, no problems. First thing I'd do is check for codes. /forums/images/graemlins/wink.gif
 
I have done a few TBI swaps.

OK, here is what "Chevrolet TPI & TBI Engine Swapping" says:

Regarding the P/N switch:
Some wiring harnesses ground the Park/Neutral wire so that the ECM always thinks the vehicle is in Neutral or Park. The reason is to prevent the SES (service engine soon) or Check engine light from being turned on due to lack of a VSS signal. The service manual states: The ECM uses the P/N signal as one of the inputs to control: Idle Air control; VSS diagnostics; EGR. If the P/N wire is grounded in drive, the EGR would be inoperative , resulting in possible detonation.
Without the P/N switch conected (grounded) the engine will run ok but engine speed may drop excessively when shifting into gear.

Regarding the VSS:
The VSS tells the ECM how fast the vehicle is going. Most people think the VSS is only used for for the lock-up torque convertor. The VSS is also used to control the EGR valve, the charcoal canister purge valve, the electric cooling fans, idle speed, and air/fuel ratio.
It must be emphasized that the VSS is used to control the idle speed when the vehicle is moving. Without the VSS the vehicle may have stalling problems under certain conditions. The reason an engine not equipped with VSS may stall is because when the ECM has the signals that indicate the engine should be idling (foot off gas, vehicle moving less than 2 MPH), idle speed is closed loop ( which is not the same as the O2 sensor running closed loop) and the ECM will try to maintain a programmed idle speed. If the vehicle is moving, the ECM opens the IAC (idle air control) a programmed amount, regardless of engine speed, which is usually a position that will make the engine idle about 50-100 RPM above the programmed idle speed. Stalling can occur when the vehicle is in the over-run condition (foot off gas- engine speed above the programmed idle speed) because the ECM will try to lower the idle speed to the stationary programmed speed. The IAC may not be able to open rapidly enough to prevent the engine from stalling.
Raising the minimum idle speed with the adjusting screw can eliminate stalling, but the engine will not run optimally without a VSS. Some Chevrolet engines are programmed to run lean under highway mode. Without VSS the ECM will not get the signals to run the engine for best fuel economy. There are also other programs in the ECM which depend on the VSS.
 
I'm going to be doing a TBI swap on my 74 which has the sm465. Am I going to be running into any trouble since I dont have this VSS setup?
 
Ok, now with a th350 will I be able to hook the vss up, O'm looking to do this TBI and you guys have me pulling my hair out.... /forums/images/graemlins/1zhelp.gif /forums/images/graemlins/rotfl.gif
 
Waxer, do you have your system yet...I'm trying to get one right now... /forums/images/graemlins/thumb.gif
 
The "early" TBI setups "read" the vehicle speed from the speedometer cable. Using a stock '81+ speedometer with VSS is an easy fix. (since all 700R4's that I know of used VSS as well, that means almost all trucks minus 400/465 equipped got VSS from about '82) May look crummy, but it should be pretty cheap to get a later speedometer cable and retrofit the later speedometer setup/VSS setup.

Either that, or you can go with one of the JTR VSS setups.
 
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FWIW, and not trying to start anything, I have done four TBI swaps, all using the GM harness, all were put into manual trans vehicles. No VSS, no problems. First thing I'd do is check for codes. /forums/images/graemlins/wink.gif

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If you've never done it right, you can't possibly be able to say with any authority whatsoever that it's not wrong.

I've run my car (with 86-89 TPI ECM) in "Painless Mode" for kicks and I've run it properly. It's manual trans. as well.

You are wrong. However, if you feel that your authority usurps that of GM engineers, I'm sure they're accepting resumes. Now read the post beneath yours for details and quit misleading fellow CK5ers.
 
when I swapped in an NV4500 for the 700 in my '87K5 TBI, the GM parts guy sold me a manual PROM. Questions:
1. differences between AT and manual PROMs?
2. Is the PN switch fed to the ECU on my '87? (it stays in Park now all the time, &runs OK)
3. On my '77 350 pickup, I'm doing a TBI swap. What kind
of intake manifold to use? '87 &up mnifolds won't fit the
older 350s, right?
thanks.
 
ok, really really dumb question since i'm going to start building a rock buggy in a few months with a 4.3tbi and a 465. Where does a manual tranmission tbi engine get a vss signal from? I assume from earlier posts that the prom in the ecm is different too??
 
You can add the VSS to any system with a chip made to accept it, and by connecting it up to the proper pins at the ECM. You can get the VSS info from customefis.com too... he's got one for less than $85 IIRC... it will plug directly into any cable-driven speedo gear, and then the cable attaches to it. This allows you to add the VSS functionality easily to any system! /forums/images/graemlins/wink.gif

-Dan
 
[ QUOTE ]
1. differences between AT and manual PROMs?
2. Is the PN switch fed to the ECU on my '87? (it stays in Park now all the time, &runs OK)
3. On my '77 350 pickup, I'm doing a TBI swap. What kind
of intake manifold to use? '87 &up mnifolds won't fit the
older 350s, right

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1. The differences between the manual and auto versions relate to the ECM output to the TCC (pre electronic control autos), and the ECM input from the P/N (auto) vice from a switch on the clutch - AFAIK. I have not wired a TBI manual trany setup - but I could look up the differences in my wiring diagrams.

2. I'm not sure what the situation is on your 87 when you say it stays in "park". But the ECM does use the signal from the Park/neutral switch. Generally it is better to leave the P/N switch ungrounded all the time (as if it were in Drive), if it can not be hooked up so that it will only be grounded in Park/Neutral. Although some aftermarket harnesses ground the P/N signal all the time.


3. The TBI (post 87 V8) intake can be modified fairly easily (subjective term) to fit pre 87 heads. I have done it and know of several others on the site who have done it. It involves re-orienting the 4 center intake manifold holes to allow mating to the heads (same orientation as the end holes on the intake manifold). Use a drill bit/dremel tool - 8 hours or so of work, depending on your motivation/attention to detail.
 
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