injector pulse width

[George M. Dailey]

At 09:41 AM 3/29/96, you wrote:
>
>     
>>Per Frank "Choco" Munday's book, TPFI, he states that 305/350 injectors 
>>will work reasonably well if exchanged as a complete set. This refers to 
>>the MAF type TPI systems up to '89, and exclude your '85 baby (even though 
>>it's MAF equiped). His book only covers the '86-'89 models, but I think the 
>>injector swaping rule will apply to your system also since it's a MAF type. 
>>Choco goes on to say that he can not tell the difference below 4,500rpm. 
>>Thats big in small and small in big.
>>
>>There are differences in the operating pressures. Per chilton, 44psi for 
>>5.0 & 37psi for 5.7
>     
>>22lbs/hr flow rate for the 350 per Ben Watsons chevy fuel injection book (no 
>>305 data).
>     
>>BTW guys, The '89 TPI in my '58 is running great! All bugs have been worked 
>>out and I've clocked over 600 trouble free city miles already. The R700 is 
>>comming soon.
>     
>>Dan, if you can give the symtoms, I sure one of us gurus could help.
>     
>>Good luck
>>GMD
>
>Thanx for the info.
>
>The system is infact of a TPI of a 305 '85 F-body according to the fuel rail 
>number.  However the system is now MAP sensing.  Can anyone confirm that
what I 
>have done seem right.  I have the ECU water temp sensor mounted in one of the 
>three holes in the front of the manifold, the air temp sensor is mounted in
the 
>hole on the underside at the back of the plenumb chamber, and the MAP ensor 
>vacuum line is taken of the back corner of the plenumb chamber.
>
>The cam is:     inlet   -  open 23 deg, close 61 deg  (I think)
>                exhaust -  open 68 deg, close 26 deg  (I think)
>
>The engine only seem to run evenly at a stoic of 11.5, CO=5%-7% (very rich) at 
>idle.  When you try and improve on this and actually load up the engine, the 
>engine starts to jerk around quite violently and only seem to settle down 
>slightly in the low rpm range when you give it lots of fuel.
>
>Is it possible to calculate a theoretical fuel map for my computer, either
a VE 
>value or an inject time pulse width for the rpm range that we can follow ? 
>
>If this is possible can someone please send me the formulas ?
>
>By the way, I'm using the old type HEI dizzy, and when we checked the
ignition, 
>it looked like one bank of the engine had a problem (the pulses were not all 
>level, but went up and down and up and down) but I have been told that the
wrong
>air/fuel ratio can cause this.  Anyone have any ideas ?
>
>Is it a timing problem ?  Is it a fuel problem ?
>
>Much help needed here
>
>
>Dan     dzorde at aesprodata.com.au
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Dan, If I were you, I would START by follow this GENERAL diagnostic procedure.

Start writting down things you have checked and there results. There are a
lot of things that can fail on a TPI system.

I'm almost sure that the '85 TPI used a MAP and MAF sensor. The '85 is a
stand alone system as far as electronics are concerned.

Verify that the ignition system is working properly and that each plug is
firing.

Check your fuel pressure and make sure that it is being Vacuume compensated.
There should be no fuel on the Vacuume side of the pressure regulator.


GET A SERVICE MANUAL for the system. Chilton or if possible, OEM. What type
of trouble codes are being sent? I can't give much more advice without
knowing more (a lot more) details. In general, be certian the mechanical
portion of the engine is in good shape. Look for the simple things first
like cold start valve leaks, vacuume leaks.

Good luck and be patient & persistant.

GMD