Sn8k09

Finally got some time to work on my crank no start 90 Z28. (got me this 90 z28 that sat for 14 years, so it had multiple issues)

initially: engine starts shortly by jumping starter and shooting starting fluid

no crank- disabled Vats
fuel not running - replaced pump
has spark
fuel pump primes and at 43 psi at schrader valve
replaced fuel injectors - still crank but no start
replaced distributor only because i got a great deal on one - still no start
ecm send signal to injectors - tested via noid light- however it seems interminent

read up on the purpose of the TPS sensor and tested it:

using voltmeter:

key on:
Top wire:12v
Middle:7v minimum and up to 9v
lower: 7v

disconnect wires from Tps and tested the connection with out it

Top Wire 12v
middle: 3.5v
lower: 7v


the middle 7v reading cannot be adjusted at all

checked resistance on tps and it starts at 800 and increases gradually..with the lever

i am leaning towards bad TPS

aliceempire

iTrader: (14)

I don't think I've ran into a TPs that stopped an engine from running. You have fuel, right? You have spark still? Check the plugs. What do they look like? Gassy? Clean? Black? Etc? That'll help tell you if you are lean or rich or possibly out of time. Use this to check/adjust the tps. https://www.thirdgen.org/tpimod2/

ASE doc

I'm confused. The TPS is a 5 volt sensor. It gets 5 volt reference from the ECM, an ECM ground, and has a signal circuit back to the ECM that should vary from about .6v or so closed throttle to 4.5v or so at WOT. Closed throttle voltage can be as high as 1 volt on the '90 models without causing trouble. There is no 12 volt feed to the TPS.

One thing that strikes me is you say you bypassed the VATS. Did you actually install a VATS bypass, so that the ECM receives the fuel enable signal? If not, there is no injector pulse from the ECM.

Sn8k09

Vats bypass: resistor underneath steering wheel,
previous owner had replaced steering wheel and it would not crank over because the new key that came with the new steering wheel was not matching on the resistance that the ecm was looking for.

After I installed the resistor it started to crank but no start

I have injector pulse as I tested with a noid light. I have spark as I can start it shortly with starting fluid

So something is killing the initial injector pulse right? Or so I think


Tps test:
Key on:
Dvom, red lead on red battery and black lead on top tps wire: 12v

Red lead on battery black on middle tps wire: 7 To 9v

Red lead on battery and black on bottom tps connection: 7v

Am I testing it wrong?

Unhooked tps and tested the actual connector without the sensor , tested same way and results:
12v top
3.5v middle
7v bottom

My latest idea from searching the boards is that if ecm is being sent high voltage from tps that it's (flooded) then it shuts the injector reference...

Maybe?

Regardless I think the tps is bad and one is on it's way

RED85TPI

The middle wire on the TPS should read .54v (throttle closed) and around 4v (WOT). The voltage should increase evenly when opening the throttle. Just put your ground from your voltmeter on a grounded bolt and your hot on the middle pin (with the TPS connected of course).

bigal55

iTrader: (1)

Yes, you are testing it wrong. As Red said, put your black (com) lead from the meter to a good ground or use the battery negative terminal. Use the red lead as your test probe. When ever voltage tests are made, they are ALWAYS referenced to ground. That is why your TPS readings don't make sense. If you subtract the 7 volts from your batteries 12 volts, you would have 5 volts to ground as ASEdoc has said. By the same reasoning, you have ground (12 volt reading) and your signal back to the ECM is 12 - 3.5 = 8.5 volts. TPS is bad. Re-check those numbers again with your com lead to ground and probe with the red lead. I'm pretty sure you will see the TPS is bad. HTH!

ASE doc

The only way the TPS could cause no injector pulse is if the ECM is seeing 80%+ throttle. It would go into "clear flood" and shut down injectors. Make sure you have no more than 1 volt on the signal wire of the TPS. I assume you have wiring diagrams so you can be sure of where to test.

A scan tool is great to have at this point since it will actually let you see what the ECM is seeing, such as throttle % and what it's commanding, such as commanded injector pulsewidth. Winaldl is a free download. So is Tunerpro, though they do ask for a donation(it's worth it). The cable you need is available on the Moates website and other sources online. Check it out. There are people on this forum who use it on their thirdgens. There are also older scan tools that support the OBDI GMs that you can buy pretty cheap.

ASE doc

I assume you have power to the injectors with key on. If not, check the two INJ fuses in the underdash fuse panel.

Sn8k09

After new tps, still no start. So I checked my timing and it was way off, found tdc and bang... Starts like a charm.

Only ran it for about 5 min because it's in my garage and previous owner cut the muffler pipe right before the exhaust. So the fumes are no Bueno ,,

As work and time permits, will adjust timing with timing light and will re check tps as its throwing a code 22