I have recently bought a c4 corvette
1990 c4 corvette
L98
160k miles

the previous owner had put on: (to my knowledge)
Aftermarket Throttle body (BBK power plus)
Aftermarket fuel pressure regulator
aftermarket exhaust
push to start button
Various electrical bypasses/rewiring
seems to have cut into the injector harness to do some rewiring
also seems to have shoved a fuse into a two prong sensor to complete the circuit which resides under the coolant tank.

The issue: Recently when I start the car it has a serious issue staying at a steady idle, when I bought it I was able to drive and over and hour home, and the next day it ran just fine (I adjusted timing slightly to make it a steadier idle).

I really want to keep the TPI system, and try to be as pure as possible for the car, so I was wondering if anyone had a good checklist to go down for parts to either check or are cheap enough to replace (sub 10$) that could be the culprit. I don’t know if it’s the ECM struggling to keep up with new parts, or if it’s a miscommunication somewhere.

I also have parts to carburete it, but I really want to get power out of a TPI system, but it just seems like the power ceiling would be a lot lower than I am hoping.

If any other information is required, please just let me know and I can respond to the best of my ability

 

I'd be more worried about the cutting up of the harness than anything else. I can't emphasize enough how you should pick up a Factory Service Manual (FSM). I'd also be wondering why they changed to an aftermarket fuel pressure regulator; is it adjustable?

I think there are a lot of factors and unfortunately, there's no clear starting point other than "un-cluster f**k" what the PO did.

 

not adjustable from what I see, I really think the PO was just throwing stuff at it to see if it works, trying to revamp the car, told me he was working on the HVAC, put a crappy car play and the push to start in

 

You might want to verify your timing and do a minimum idle adjustment. Should be 6 degrees BTDC with the set timing connector unplugged (single tan wire near brake booster)

 

 

For some reason it is not showing the page from manual, maybe it will show up on your screen.

 

do you have a digital copy of this manual? Or is it a per user kinda thing

 

I scanned every page of my manual and it’s stored on my phone.

 

Would you mind sharing it? I plan on getting a Chilton repair manual soon, but for the time being I am outta luck for good diagrams of the car

 

Id skip the Chiltons are get the General Motors manual. Readily available even Amazon.

I feel your pain on PO hacked wiring. C4 wiring is complicated enough in stock form. I try usually try to get everything back to stock and if I cant I either label it or put instructions in the glove box. Helps me or the next guy somewhere down the line.

 

To your knowledge, does the GM manual have wiring diagrams for the L98? I’m really just looking for diagrams of where stuff lives so I don’t have to bother the internet with stupid questions I couldn’t answer myself.

 

I would also suggest checking the fuel pressure at the fuel rail and, if possible, hooking to a laptop with tunerpro (or equivalent) to monitor sensor values (TPS, coolant temp, IAC, O2, etc). Reading sensor values is critical for diagnosing issues with these cars.

Where are you located? City/state?

 

Aberdeen MD, I am going to be honest I think the PO disconnected and removed the coolant temp sensor, I am troubleshooting tonight to see what is throwing issues, and bringing in a new battery since it doesn’t want to stay alive (goodbye courtesy light fuse)

 

The CTS provides information to computer to allow proper fuel flow for cold start (open loop) into closed loop. You saying that the po messed with the wiring to the extend you have said I really have concerns. As already stated, get both books of the GM FSM. One book provides all the electrical diagrams to you can use to compare to what was changed by the po..

 

me and my brothers running theory (since I was able to drive it home) is that open loop is miserable for the car due to missing sensors, so I’m going and essentially going to baby the throttle till it gets there to see if the engine runs smooth in closed loop.

 

My manual is for 1986
You will want one for your year

 

I second the suggestion to hook up TunerproRT or some sort of scanner to look at the running data coming out of the ECM. That alone will tell you A LOT.

I'm assuming the PO hasn't messed with the ECM? Might be worth it to open the access cover on the ECM and see if the factory PROM is in there.

For example, If the PO screwed around with the fuel pressure and the PROM chip is factory, then the fueling is going to be screwed up.