North West Corvette Guru

[Dave Burns]

Hi, new member but long time owner here looking for a recommendation. My 89 C4 has been off the road since pre Covid, it was pushed in to the garage with a failed fuel pump and for one reason or another sat there until this year.
I fitted a new fuel pump and it fired straight up no problem, but its not at all happy at tick over and gets worse as it gets hotter. I have replaced plugs leads distributor cap rotor arm coil TPS and ICV none of which have really made a difference.
I have used the paper clip on the diagnostic port and am not getting any fault codes, so I'm running out of things to swap.
So my question is, can anyone recommend anywhere in the North West who really knows these cars.

 

[Steven Smith]

Have you put some fresh fuel in it ?

 

[Dave Burns]

Yes forgot to mention that drained old fuel and filled with E5

 

[Steven Smith]

Have you cleaned out the throttle body and checked the voltage at the TPS sensor?

 

[teamzr1]

With the gas sitting that long, did you also change the fuel filter and
using a fuel gauge pressure tool to connect to the fuel rail, I think back then it should be 43 PSI
Maybe the fuel injectors are clogged up, and you need to use a good gas/injector cleaner

Best is to connect an OBD-I scanner and see what is not working well

 

[Dave Burns]

Have you cleaned out the throttle body and checked the voltage at the TPS sensor?

Yes and yes

 

[Dave Burns]

With the gas sitting that long, did you also change the fuel filter and
using a fuel gauge pressure tool to connect to the fuel rail, I think back then it should be 43 PSI
Maybe the fuel injectors are clogged up, and you need to use a good gas/injector cleaner

Best is to connect an OBD-I scanner and see what is not working well

Done the filter and run fuel injection cleaner through the tank

 

[Blackzed]

Do these have ignition modules?
My old 86 Trans Am had one go bad and it ran very rough.

 

[teamzr1]

Yes, the 1989 C4 has EST and ESC

Attached below the OP should save this PDF as it has all the GM engineering design specs, option codes, and more

Interesting, this has a GM screwup in that all the specs for the ZR-1 show as a 1989 model
when it did not go into production until another year of 1990

 

[Mr. Cricket]

Parts USA are the go to guys for 'newer' Corvettes and I think that may include C4's. Supporting vendor that gives a tidy discount for club members. Rates reduced from £90 to £60 and 10% on parts



Parts U S A

​

www.partsusa.co.uk
13 The Gate Centre, Bredbury Park Way, Stockport SK6 2SN · ~19.8 mi
0161 872 7744

Edit, just spoke with Chris at Parts USA and yes they work on C4's. All NW members use them and have nothing but good to say about them

 

[Dave Burns]

Parts USA are the go to guys for 'newer' Corvettes and I think that may include C4's. Supporting vendor that gives a tidy discount for club members. Rates reduced from £90 to £60 and 10% on parts



Parts U S A

​

www.partsusa.co.uk
13 The Gate Centre, Bredbury Park Way, Stockport SK6 2SN · ~19.8 mi
0161 872 7744

Edit, just spoke with Chris at Parts USA and yes they work on C4's. All NW members use them and have nothing but good to say about them

Tried them they were not keen on looking at a C4 bit to old for their software

 

[FelixP]

Check the coolant temp sensor on the front of the intake. If it's failed or the wiring is dodgy it'll think it's freezing cold and run too rich. Unplug the MAF, does it change the running condition? Could be worth swapping the MAF relays.

Are they the original fuel injectors? If so they're probably due replacement. You can get new Bosch III from Fuel Injector connection. Try unplugging the injectors and checking the resistance on them. They should all be similar.

It'll be something simple, be methodical and work through one thing at a time once you've proven it.