Rob 97 Z28

iTrader: (3)

Trying to get the '91 running top notch while I wait on my trans for the new engine...Car starts good when its been sitting all night. Fires right up in the morning, once its warmed up she runs rich.It idles at a normal RPM, slightly drops for a short amount of time then picks up a bit more...like its going into closed loop, realizes its idling to low for the amount of fuel its recieving then goes back to an open loop like idle. Real rich, just dumping fuel. Drained the oil twice in the last 10 days, theres more fuel in the oil than in the fuel tank. Been trouble shooting the car like cRaZy! Heres what I know...

Plugs are new but already carboned up
Ignition system, fuel injectors was all replaced before I bought the car
looking under the top half of the upper plenum looks like the FPR etc was also replaced

Car was throwing a code 35 but SES would shut itself off. It has it stored but I can't get it to turn (SES) light back on by itself. Supposedly the ECM is okay, it flashes 12 but I am questioning its legitamacy. Been reading through my GM tech manual for trouble shoot. I know the IAC and TPS play a huge role with the fuel system. Code 35 has inadventently lead me to check the IAC & TPS wiring itself. I had checked the ground for the TPS, its got continuity, check the TPS siginal wire, which should be between .29-.98. I got 4.9 volts?!?! Which tells me that the ECM THINKS the car is at WOT when its @ idle! Heres my questions

1- TPS voltage changes once the car is in closed loop correct?

2- Is it possible that there IS a fault with the ECM that it can't detect itself? Explaining why the SES light illuminates then turns itself off, and wont stay on when it brings itself out of closed loop then back to a low idle closed loop?

3- Is there any way I can trick the ECM into thinking the TPS signal is normal ( .29-.98 volts) ?

Continuing on, MAP sensor shares a common circuit with the TPS. CKT 474. The ground for the MAP has been "patched up" right behind the pigtail. Which helps narrow this down but means I'll have to find a way to rewire it. Check the voltage at the MAP and like the TPS its got 5.0 volts sending a low manifold vaccum signal (WOT) to the ECM...proceeding to scrach my head some more...


Taking my multimeter and watching for changes in TPS voltage I took the MAP sensor ground and grounded to see if the TPS dropped from 4.9 volts down to .29-.98 ...No luck...

Maverick H1L

iTrader: (8)

Are you sure you're probing the right wire on the TPS for the signal? It should be the light blue one for the signal. You're aiming for about .55 VDC on the adjustment.

Same for the MAP. You're looking for the light green wire as the signal.

I'm not trying to make you sound like an idiot, I'm just making sure before we go any further.

Anyways, do you have fuel in the FPR vacuum line, and is the line hooked up to manifold vacuum instead of ported?

And, can you possibly tell if the injectors are GM, and if they are, can you read the part number(s)? It could be that your injectors are too big. You're not throwing code 45, are you?

Six_Shooter

iTrader: (2)

Closed or open loop has NO effect on TPS or MAP voltage. OK, to satisfy the nit-pickers and hair splitters.... MAP voltage can be effected by going into closed loop, but ONLY as a result of a change in the way the engine itself runs, there is no direct electrical change as a result of the ECM entering or exiting closed loop.

If the TPS signal is indeed at 4.5V, the car should not start. It should be in a mode called "Clear Flood Mode", where the injectors are very nearly shut off, while cranking.

I also have to question whether you are probing the signal wire or the 5V refernce wire. The reference wire should be grey, where as the TPS signal wire is, as stated blue, Map is also as stated, green.

Brett1957

Ok, I am having the same prob. How do u get the ECM out of "clear flood mode"??? I've read 20 threads about this and it all points to this prob, but no one can tell me how to fix the problem?

Maverick H1L

iTrader: (8)

You need to make sure the TPS signal wire isn't carrying 5V to the ECM by disconnecting it from the sensor and probing the blue wire with a voltmeter. If the blue wire does have 4-5V, then it's shorted to the gray wire somewhere in the harness.