Re: 91 ZR-1 Cutting Out Under Load
 

Greg,
Let me run this by you about the O2 sensor #'s. The sensors should respond to changes in the A/F ratio as adjusted by the ECM, therefore there will be no set number in mV's that appears. Near as I can figure if the mV's are not constantly varying then the sensors are getting lazy and or going out to lunch. They react or read what has already been done by the ECM to the A/F ratio via the injector pulse width changes. In short I think they either work or don't with a lazy phase prior to quiting all together.

I still don't like the low fuel PSI readings.....using the A/C gauge set not withstanding....book says 48 - 55 PSI in the KOEO test for both 1* & 2* pumps, and a 3 - 10 lb drop with the motor at idle speed as within specs. The f/f is an easy swap & might yield something, it's also the cheapest part in the fuel system!:) I know I tested my fuel PSI when I was having injector trouble and the difference between a new filter and the one that was in the car for 8K miles was dramatic, oh yea the OEM filter was still in my car when it was delivered.....a 15 yr old f/f is not my idea of good maintenance. I do it every yr along with some other stuff.

The regulator seems to either work or not, according to the FSM. Oh, the only variable is it's vacuum source....it is good or the hose is at fault. Check to see the hose is okay and that there is no fuel in the hose. Fuel in the hose is the tell tail that the regulator is kaput.

:cheers:
Tom

Re: 91 ZR-1 Cutting Out Under Load
 

I hear ya' Tom. I wouldn't be surprised if my car still has the original OEM filter. I'll definitely change that and see what it does to my pressure.

As for O2 reading, yes they change rapidly and dramatically at idle and at cruise speed. At full throttle, they go up way high and should be somewhere around .750-.900 and stay in a certain range. That's how we tell how to adjust our adjustable fuel pressure regulators at the drag strip. On tuned port injection cars(I still have one with a Lingenfelter 383) the full throttle O2 readings should be around .760-.790. On LT-1 cars, optimal readings are around .860-.910. I just can't remember what ZR-1's are supposed to be.

Using these full throttle readings is how I discovered once on my ZR-1 that a little 5 cent clip had fallen off the right side secondary flap actuator. Without that actuator opening the secondary air flaps, the O2 senser readings on the right side went wacky.

Re: 91 ZR-1 Cutting Out Under Load
 

GM uses short-term(integrator) and long-term(block-learn) fuel numbers. They are as they say, fuel maps of different time lengths. The short-term numbers will be very bumpy and jump all over the place, even at idle. This short-term map varies fuel for any reason such as a lead foot, hilly route, large load, a/c,vacuum leak, etc. It instantly adjusts with (in GM's case) above the number 128(the mean desired fuel delivery point) representing lean or adding fuel, and below 128 as rich and subtracting fuel. The block learn or long term numbers are a smoothed out picture of this fuel delivery. The same 128 number representing the optimum mean point. Above 128 and the PCM is needing to add fuel over the long term and vice-versa.

O2's - L- .10 to .69 R- .10 to .74 What is the rate of fluctuation? Slow/Fast?
Block Learn L- 136 R- 130 You are adding fuel, not that much though
Integrator L- 127 to130 R- 128 to 130
TPS .44 At idle or key in the run position should be around .54 volts


When testing injectors, remember that checking the resistence is only 1 of the things that can fail. You can have it also fail by leaking, spray and flow issues.

Consider spending the ten bucks on a fuel filter, make sure you have line wrenches for the job.

Re: 91 ZR-1 Cutting Out Under Load
 

O2's at idle are fluctuating as normal, very quickly.

Trying to remember on the TPS, is the ZR1 TPS non-adjustable or the same as the TPI cars at the time that should be adjusted to .54 +/- .05 ?

Re: 91 ZR-1 Cutting Out Under Load
 

It is adjustable. Takes a T-25 to undo the screws. It's auto correcting within certain limits. And .44 is not with those limits.

Re: 91 ZR-1 Cutting Out Under Load
 

Finally got a chance to work on the beast again. I pulled the fuel filter out and it had come apart, it rattled. That gave me some hope but I could still easily blow thru it. I put the new filter on and still had the same fuel pressure reading. Went out for a drive, same problem, stutters under acceleration. I recorded my O2 sensor readings and they appear to be just fine. Under full throttle acceleration the O2 readings are:

Left: .84 - .87
Right: .85 - .88

I'm now officially stumped. With the fuel filter coming apart, I wonder if a bunch of crap got into the injectors ??? When I undid the fuel lines and pulled them away from the original filter, I put a bowl under the lines to catch the fuel. The bowl got a bunch of dark particles in it. I wonder if some of that stuff made it into the injectors??? You would think however if the injectors were clogged up, the O2 readings at full throttle would go lean while stumbling.

I don't know, officially stumped now.

Re: 91 ZR-1 Cutting Out Under Load
 

Yikes, hate chasing problems like that, hope it gets solved soon.


Jeff, I take it the setting on the TPS is supposed to be .54?
Sorry bout the hijack.

Re: 91 ZR-1 Cutting Out Under Load
 

As far as the TPS, they are not adjustable. Mine is .44V at idle and 4.4V at full throttle. You can loosen the 2 screws holding the TPS and move it just a tiny, tiny amount that doesn't even affect the numbers. This TPS does not have the adjustable slots like on earlier TPI motors.

Re: 91 ZR-1 Cutting Out Under Load
 

Ok, I got confused...thought they had screws for adustment, but now its clear they arent. Good news actually, one less thing to worry about

Re: 91 ZR-1 Cutting Out Under Load
 

It is adjustable, it swings up and down after loosening the two screws that hold it on. The acceptable range is .46 to .62 volts at closed throttle.