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Re: [T3] 72 square, rough idle, #1 missing?

On 7 Mar 2002, at 19:29, Drake Lawson wrote:

> Found a document on-line for the vacuum connections
> http://home.pacbell.net/lordling/hoses_t3.jpg 

These diagrams are from the Henry Elfrink book which is probably the best 
ever written on our FI. Unfortunately these have long been out of print, but 
they occasionally turn up used. I don't have any extras at this time.   

Yes, this is the correct one for your 72.   

> And did a quickie Photoshop edit of what I have in my car
> http://home.pacbell.net/lordling/drakes_hoses_t3.jpg Or should I say the way
> it used to be, now the vac advance on the dist is connected directly to the
> port on the throttle body. And the small port on the decel valve is connected
> to nothing. I left the large hoses in place until I can get some caps to cap
> off the two ports on the air cleaner they are currently connected to. 

Okay, that's fine now.  

> >Quick follow-up: On the vacuum canister arm inside the dist, there is a 4
> >digit number. What is it on the dist that you have. 

> #265 

Okay, that's the 68-71 MT vac can. It will work fine.  

> >Just to clarify, all the 72 came with a vacuum advance/retard (2 hoses.) If
> >yours doesn't, then it is either not a 72, or it was changed by someone in the
> >past. Does your chassis number have a 2 in the 3rd digit?

> Yes VIN #362XXXXXXX 

Okay, it's really a 72.  ;-)  (mistakes happen, and often get us confused 

> >What's your engine number? It's stamped in the right half of the case just
> >along the centerline, just ahead of the breather. 

> Not sure at the moment, have to check it later. At any rate this is a rebuilt
> longblock I just purchased and installed. 

Did you buy it with this intake air distributor and dist? If so, they just gave 
you something close, but not quite "72," but I think it will be fine.  

> I made a mistake in my earlier post, when I stated where the hoses on the
> decel valve were connected. I must have been thinking about them being
> connected in teh only places that would make sense and work, rather than
> where they are connected on my car :). 

Right, it's doing nothing now, plus you're really better off without it.  

> The only interior ports on my throttle body are currently being used, so I
> dont really know where the decel valve would have connected. It is not
> connected now though. I know that the thing is connected incorrectly in my
> car. One of the large ports goes to the air cleaner, and the other large port
> goes to the air cleaner....that cant/wont do anything. 

You probably don't have a "72" intake air distributor on there, but that's not 
really a problem. Unless you need those extra ports, you don't need the 
different IAD.  

> I have one port near the butterfly, and thats what the vacuum adv is now
> connected to...directly 

Unless you've already done it, you should follow the hoses on your diagrams 
to see if there are some extra ports there which you haven't seen, just so 
you can block them off.  

> They are all tight now, I removed all the pins from the connectors and
> squeezed them all a little. Now they feel like they should. 


> After switching the vac advance so that it was connected to directly to the
> throttle body, and squeezing the connectors on the FI connections. I fired
> it up, then took it for a drive just to make sure everything was at least the
> same or better than it was. The car still lopes at idle, though it seems to
> run fine (much better than it did) while driving. 

How much does it lope? If it is going up and down several hundred RPM (to 
maybe 1400) then this is just a simple matter of your idle speed being set 
too high. The ECU cuts off the gas if it senses that the RPMs are above 
some threshold while the throttle is on idle; this is to reduce emissions while 
coasting to a stop.  

> Actually at idle it sounds something like my old bug, with a old, tired, low
> compression 1600 DP, a 110 cam, and a weber progressive. 

> I am not entirely sure what the problem is, is it runing too rich and loading
> up at idle? there are those extra resistors that someone put in line with the
> head temp sensor. But if those are removed then the idle will drop to a point
> where it barely runs. Shes going on a 400 mile round trip this weekend, maybe
> the gods will favor me and everythign will be fine when I get back :) 

I don't know what to make of the extra resistor. I'd like to suggest that you 
jumper around it, at least temporarily, to see if you can find what the REAL 
problem was that prompted someone to put it in there. If the idle drops, you'll 
have to raise it back up. See how it drives with the resistor jumped, perhaps 
it will clear up if it gets driven a bit. (I'm grasping at straws here....)  

This temp sensor is a neg temp coeff device, so adding resistance makes 
the ECU think the engine is colder than it really is. It should respond by 
richening the mixture. The only thing that I have seen on a 72 that made the 
mixture too lean, was a pressure sensor where the bellows must have leaked 
over 20 years and slowly leaned out the engine. You could try to find another 
PS to substitute.  

Have you checked the fuel pressure? It should be a constant 30 psi.  

Two things to check:  

1) Put a clean hose on your pressure sensor and suck on it. Make sure it 
holds vacuum pretty well. If the diaphram in it is torn, it won't control 

2) Check the charging system regulating voltage. It should be 14.1-14.4V, 
measured at the battery, at medium RPM, after warming up the engine on a 
short drive. If the voltage is low, the FI will run rich. If yours is below 13.5V, 
replace the voltage regulator with a genuine Bosch. This is a common "FI" 

Jim Adney
Madison, WI 53711-3054

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