91 ZR-1 Cutting Out Under Load

[GregCrowe]

Originally Posted by XfireZ51

Did you ever pull the fuel pumps?
I didn't catch how many miles were on the car but the 30psi at idle isn't right. Has that been rectified? If not and you've changed the fuel filter, I would look at the sock filter on both pumps. They may be plugged to the point that they'll look like they are being sucked in by pumps. In that case I would replace the pumps since they probably been overheating trying to get fuel out. I had problem with my fuel pump filter causing the secondaries to shut down due to lean O2.

Fuel pumps test out OK. I replaced the FP Regulator during the injector swap. My FP is normal now.

[GregCrowe]

Originally Posted by XfireZ51

Fuel system is the first thing on both these lists. The stumbling that happens when the accelerator is moved can be due to the lack of or insufficient pump shot. Without sufficient fuel pressure there isn't enough fuel and the mixture goes lean causing the momentary stumble and lack of power.

The problem is not consistant with a fuel problem. It feels very "electrical" like the spark just disappears for a split second. The hotter the car, the more it has heat synched, the worse the problem.

[GregCrowe]

Looking at these coils on both Auto Zone and OReillys websites and it looks like the ZR-1 coils are the same generic thing as the 3 coils on a 3.8L V6 which I know are always problems. Is that right? The same coil? I can't even tell you how many of those things I've replaced on 3.8L's.

[LT5-Lee]

Originally Posted by GregCrowe

Lee, I'm so disgusted with this car. I can't seem to be able to fix it. It's been almost 3 years since my first post and the car has just sat in the garage. I've only driven it maybe 10 miles. At this point I'm totally worn out on it and tired of throwing money at it. The only thing I can figure now that might be a possibility is:

1. ECM
2. Ignition Control Module
3. Coils

I'm sick of pulling the plenum. I'd love to try another ECM and see if that fixes it. Someone out here once offered to let me try their spare but never replied back. My ZR1 just sits in the garage. I don't drive it, can't sell it like this........ totally disgusted with it. It's a giant paperweight taking up space in my garage.

There you go, JeffVette to the rescue.=D>

[Tyler Townsley]

Originally Posted by GregCrowe

The problem is not consistant with a fuel problem. It feels very "electrical" like the spark just disappears for a split second. The hotter the car, the more it has heat synched, the worse the problem.

Beg borrow or steel a fuel pressure guage. Hook it up and pop the hood enough to feed the hose out and tape the guage to the windshield. Take the car for a run watch the pressure when the symtoms happen, fuel starvation mimics an electrical problem on a efi car since it will show up as a lean condition at a cyl much like a spark problem at same cyl. Its a cheap check.

Another check is the plugs, do they show a lean condition? If they show soot then one could suspect spark, if lean then fuel.

A quick check on spark is to pull all plugs then take a good plug and put it in each wire one at a time and lay it on the plenum. Crank motor and watch the spark all cyl should show same spark, I actually just pull the plug wire and put a plug in and lay it on the plenum and crank the car, in this way I can see if a cyl is bad for other reasons.

If you want to check individual injectors you can pull the plenum, lift the injector rails up, make a pigtail to connect to the injector and pulse it with 12 volts and watch the spray pattern. You will have to cycle the key to pressurize the rail but its cheap way to check them, also make resistance checks at the same time.

Tyler

[GregCrowe]

Originally Posted by Tyler Townsley

Beg borrow or steel a fuel pressure guage. Hook it up and pop the hood enough to feed the hose out and tape the guage to the windshield. Take the car for a run watch the pressure when the symtoms happen, fuel starvation mimics an electrical problem on a efi car since it will show up as a lean condition at a cyl much like a spark problem at same cyl. Its a cheap check.

Already done this, fuel pressure never drops. With the new fuel pressure regulator, pressure it exactly where it should be. Once again, I've already tested the pumps, they test fine. This is not a fuel problem. The more the car heat synchs the worse the condition gets and it has to be put under a load. Normal driving you will hardly notice it. The more the load, the more it cuts out.

Originally Posted by Tyler Townsley

Another check is the plugs, do they show a lean condition? If they show soot then one could suspect spark, if lean then fuel.

Plugs are fine, new and look great.

Originally Posted by Tyler Townsley

A quick check on spark is to pull all plugs then take a good plug and put it in each wire one at a time and lay it on the plenum. Crank motor and watch the spark all cyl should show same spark, I actually just pull the plug wire and put a plug in and lay it on the plenum and crank the car, in this way I can see if a cyl is bad for other reasons.

Plugs are new and fine, wires are new and fine. These tests will show nothing since the car has to be heat synched and put under a load. The problem is electrical.

Originally Posted by Tyler Townsley

If you want to check individual injectors you can pull the plenum, lift the injector rails up, make a pigtail to connect to the injector and pulse it with 12 volts and watch the spray pattern. You will have to cycle the key to pressurize the rail but its cheap way to check them, also make resistance checks at the same time.

Tyler

Just replaced the injectors and fuel pressure regulator. Injectors are fine. It pretty much has to be coils, ignition control module, ECM or some crazy grounding problem at this point.

[Pete]

What plugs are in your Z?
Where did you gap them?
Just because something is new don't mean sh!t.


Can somebody tell me where the RPM's would be at in 5th at 20MPH since he's problem happen's at this point.

Pete

[Tyler Townsley]

They make a DIS module checker, I have one but you might find one local as it will check a LOT of cars with these modules. You also need a scope to watch the spark as you change rpm. The advantage of the checker is you do not have to pull the plenum to check them. I had a problem with one that did not show up until 400 rpm where it began to fall apart. The dis modules are expensive when you can find them.

Re read the thread. To answer a question asked early on and never answered. The O2 sensors information is not used in WOT or power enrichment situations, the ecm jumps to calibration tables that are in the chip. The sensors used in the LT 5 are narrow band and the readings are only accurate in a VERY narrow range around stoic afr 14.7. Any voltages beyond this point high or low are meaningless. The dis module is subject to heat hense the type of grease they used when mounting it to the bottom of the plenum, it was there to promote cooling as the airflow through the plenum cools the plenum base as you drive. Not using this grease when removing/replacing the module begs for future failures. If you want to borrow my checker let me know I have lent it out in the past.

Tyler

[GregCrowe]

Originally Posted by Pete

What plugs are in your Z?
Where did you gap them?
Just because something is new don't mean sh!t.



Pete

Well, in this case it is sh!t. The car did the exact same thing before the plug change and after it. Same with plug wires, same with the fuel filter, same with injectors, same with fuel pressure regulator. Plugs are gapped at factory specs........ don't remember what that was, been over 2 years.

[GregCrowe]

Originally Posted by Tyler Townsley

They make a DIS module checker, I have one but you might find one local as it will check a LOT of cars with these modules. You also need a scope to watch the spark as you change rpm. The advantage of the checker is you do not have to pull the plenum to check them. I had a problem with one that did not show up until 400 rpm where it began to fall apart. The dis modules are expensive when you can find them.

Re read the thread. To answer a question asked early on and never answered. The O2 sensors information is not used in WOT or power enrichment situations, the ecm jumps to calibration tables that are in the chip. The sensors used in the LT 5 are narrow band and the readings are only accurate in a VERY narrow range around stoic afr 14.7. Any voltages beyond this point high or low are meaningless. The dis module is subject to heat hense the type of grease they used when mounting it to the bottom of the plenum, it was there to promote cooling as the airflow through the plenum cools the plenum base as you drive. Not using this grease when removing/replacing the module begs for future failures. If you want to borrow my checker let me know I have lent it out in the past.

Tyler

Please excuse my ignorance but what is a DIS module?