84 corvette with 87 tpi installed injector problem
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4th Gear
Joined: Jun 2017
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From: foster kentucky
84 corvette with 87 tpi installed injector problem
ok ive got a buddys corvette im working on its an 84 crossfire fi that a teenager had swapped over to an 87 tpi set up and my buddy bought it and it has had running problems from the beginning i checked it out today and it has new plugs wires cap and rotor button and has good fire so i dig deeper and the injectors are getting the pulse from the computer (ground) but the constant hot is dead on all cylinders on the drivers side but before i checked for ground and hot i ohmed the injectors and 2 were bad #1 ohmed at 15 #3 at 1 #5 at 16 and 7 at 10 so i know that 2 and 7 are junk but still dont know why there is no constant hot only on the drivers side i have checked fuses and cant find none bad and no obvious wiring issues so needless to say im in the middle of a mess that someone else has created and ready to pull my hair out any help would greatly be appreciated
Race Director
Joined: Apr 2002
Posts: 10,036
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From: Anaheim CA
The injector power is supplied by fuses INJ1 and INJ2. I don't know which one is which. This wiring diagram might help:
I have heard that some browsers don't support image tags with PDF files, so here's a direct link if you can't see the diagram:
http://www.misterpeachy.com/VettePic...24_Diagram.pdf
I have heard that some browsers don't support image tags with PDF files, so here's a direct link if you can't see the diagram:
http://www.misterpeachy.com/VettePic...24_Diagram.pdf
Thread Starter
4th Gear
Joined: Jun 2017
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From: foster kentucky
i thought about that too but its not a pressure problem its a current problem but thanks for the input
Zen Vet Master Level VII
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From: Southlake, TX
Take off the TPI and put the TBI back on. You are trying to mate two completely different systems. I'm sure it has been done, but this is not a system swap for the faint of heart. It will be difficult to figure out as the system is a bit Frankenstein.
Simply, the ECM on the TBI is set up to have two injectors theoretically pulsing four times each (four cylinders ) to cover each half of the engine. The TPI is set up for eight individual pulses from eight different injectors for each of the eight cylinders. Creating a work around would confuse the crap out of me, so I can't help.
Hit up BUCANNER on the C3 forum. He is a TBI guru and may have information on where to point you on a TBI to TPI swap.
Or find a TBI set up, bolt it on and be driving in 90 minutes:
http://www.ebay.com/itm/Corvette-Cro...pVXhz2&vxp=mtr
Last edited by billschroeder5842; Jun 29, 2017 at 03:06 PM.
Safety Car
Joined: Sep 2004
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From: Mission Viejo CA
If you want a car that you can drive, here is the tough love....
Take off the TPI and put the TBI back on. You are trying to mate two completely different systems.
Simply, the ECM on the TBI is set up to have two injectors theoretically pulsing four times each (four cylinders ) to cover each half of the engine. The TPI is set up for eight individual pulses from eight different injectors for each of the eight cylinders.
Take off the TPI and put the TBI back on. You are trying to mate two completely different systems.
Simply, the ECM on the TBI is set up to have two injectors theoretically pulsing four times each (four cylinders ) to cover each half of the engine. The TPI is set up for eight individual pulses from eight different injectors for each of the eight cylinders.
Yes, there are differences, but I'll bet this swap has been done before. The '84 uses a MAP (Manifold Absolute Pressure) sensor, while the '87 has a MAS (Mass Airflow Sensor) in the throttle body. That's the challenge! It's not clear whether the OP is using the '84 or the 87 ECM.
Zen Vet Master Level VII
Joined: Mar 2016
Posts: 5,218
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From: Southlake, TX
Yes, you are correct; I was speaking more figurative than technical. Both injectors feed the open plenum and the collective mix gets pulled down each of the runners to the cylinders. My mind (and typing fingers) were being more visual as the way the TBI is positioned, the flow naturally becomes dedicated to four (half) the engine, but theoretically every runner has access to the whole mixture.
Now, you have me competently on the electrical. I can't see how the ecm supports the individual injector fire,
Smarter men and I have done this I'm sure.
Race Director
Joined: Apr 2002
Posts: 10,036
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From: Anaheim CA
If you look closely at the diagram I posted earlier, you will see that all 8 injectors are connected together. They all fire at the same time and (obviously) some intake valves will be closed when that happens. It all averages out in the end...
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Zen Vet Master Level VII
Joined: Mar 2016
Posts: 5,218
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From: Southlake, TX
Safety Car
Joined: Sep 2004
Posts: 3,953
Likes: 550
From: Mission Viejo CA
Thread Starter
4th Gear
Joined: Jun 2017
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From: foster kentucky
I'm a confirmed CFI guy, but I think this information may not be quite accurate. In the '84, the two injectors feed into the plenum from which all eight cylinder feed, rather that each injector feeding half of the engine. Both the '84 CFI and the '87 TPI ECM's have only two injector driver circuits. The '87 injectors are gang driven, with four injectors on each driver circuit. So in the '87, the injectors sometimes fire into a port with the intake valve closed, and sometimes fire income to a port with the intake valve open! (No big deal.)
Yes, there are differences, but I'll bet this swap has been done before. The '84 uses a MAP (Manifold Absolute Pressure) sensor, while the '87 has a MAS (Mass Airflow Sensor) in the throttle body. That's the challenge! It's not clear whether the OP is using the '84 or the 87 ECM.
Yes, there are differences, but I'll bet this swap has been done before. The '84 uses a MAP (Manifold Absolute Pressure) sensor, while the '87 has a MAS (Mass Airflow Sensor) in the throttle body. That's the challenge! It's not clear whether the OP is using the '84 or the 87 ECM.