OK so back in fall i was snooping around on craigslist and found this 1992 firebird that had an old school engine swap. Long story short I own the car now and I am slowly learning some biting issues about it.

Its got an old school 350ci, 4blt main, 4bbl holley 650cfm, totally NOT the original engine, 700r4, unknown rear end, but I know its not a positrack.

Firstly the speedo, does not engage, the sensor plug and two wires look intact and run continuously from the tranny to the firewall, I am also under the impression that the entire gauge cluster runs on one fuse so I can rule that out because my tach, fuel and volt meter work.

Secondly, the dimwits that built this car ran the stock temperature sender totally wrong, they had the yellow gauge wire right but they cut the black ecm wire and ran it as a ground on the alternator mount. I purchased an old school sender, ran it in the head, ran my gauge wire, now I can get the gauge to jump but it does not read. Not sure how long it would take exactly for the engine to overheat and die but I have idled and driven it quite a bit in continuous stints, so I'm pretty confident its not overheating.

Thirdly, have any of you done an old school swap into a semi modern beast like this? What did you run into? Any tips?

Feedback greatly appreciated, thanks guys.

 

Are you sure its even a 350? Quite simple to swap manifolds on a TBI and call it a 350, then hack up the wiring like hes done. Very likely since its got the original 700R4 and open axle

Speedo could be simple or it could need extra parts. Need to know if it was a V6, TBI or TPI car originally

As long as that shade tree electrician stayed out of the dash harness you should be ok. Those are a bear to repair

The yel and blk wires ran to the CTS, not the gauge sender. Since the ECM isnt being used this sensor can go along with both wires. You want the dk GRN wire from the C100 to the single wire sender in the drivers cyl head

 

The suffix tells me my engine is a 1975 350 block. I know the car was a 305, being 1991 i suppose it could have been either throttle body or tpi. Are there ways to identify this, like dash accessories or something?

So correct me if I'm wrong, CTS meaning coolant temp sensor? Why would my old school build need one of those? They had it ran into the thermo housing, with black ran as a ground. I assumed this was the gauge sender. I don't suppose you could elaborate a bit on the dark green wire? I don't have any schematics in front of me this minute.

Thanks for the feedback, greatly appreciated.

 

Check the 8th digit of the vin

Vin e means TBI
Vin t, f, 8 are v6 and TPI. You'll need to add a buffer box on the speedo

The two wire CTS went to the ECM

The c100 is the bulkhead connector near the brake booster. Pull the loom back and find the dk grn wire, there's only one from the connector

Buy a gauge sender, a simple femal spade terminal will clip on. Hook it to the dk grn wire from the c100

 

So what you're telling me is the gauges in 3rd gens are compatible with the old single wire drivers side head sender? That's great news.

My vin tells me she was TBI, what's usually the issue when the relationship between gauge and tail-housing end?

 

3rd gens used single wire senders for coolant and oil pressure

TBI cars used an older ECM which couldn't decipher raw VSS signal, so they used an external buffer box. This box took the raw feed and converted it to usable signal before sending it to the speedo, ECM and cruise module. Your interest in this comes from it not being computer controlled at all, so as long as it's got power and hooked up the speedo should operate properly regardless of what engine is up front

V6/TPI ECMs could decode the VSS internally, so to operate the speedo, a buffer box must be added when dumping the computer

Austinthirdgen has a diagram of the buffer box

 

I understand. But where would the green wire have gone? I'll go double check but when I first got it there wasn't a loose green wire tucked away anywhere and they had a plug in the head where the sender was suppose to go...

Hmm. So as far as the speedo goes, is there a way to troubleshoot which part of the linkage between gauge and tranny has gone bad?

 

The green sender wire came from the C100 near the booster. Trace it back there and move on

Get a meter and ohm out the speedo circuit

 

Sorry to be such a goober but what resistance/reading is considered good for this circuit?