1990 ZR-1 Issues

[frantinoro]

Hello,
I got my zr-1 and it never ran right, but after sitting for a few months it's a lot worse. It misfires out the left bank, smells lean, and genuinely runs horribly. Before I parked it I put in new injectors, coils, plugs, and plug wires, so I can't tell much from the plugs, but they look fine. I resealed the IH and all the vacuum lines for the secondaries, and when jumpering them they work as they should. My only issue I've found so far is I'm only getting 38 psi at idle, and 35 at wot. Both pumps are suburban pumps and new, new o2s as well, and both pumps work when jumpered. I contacted Phil who rebuilds the FPRs and he doesn't think it's my fpr because it doesn't leak. Does anyone else have anything I can test? Thanks again

[A26B]

One obvious problem is your low fuel pressure.

Have you performed the static test (key on, engine off) individually, for each of your fuel pumps?

If the static test is still low, I suggest you remove the Fuel Pump Sender Assembly & inspect all the hoses & components for breaks or leaks.

If the inspection didn't reveal any leakage, then it may be one or both of the fuel pumps. Observe static fuel pressure. With Key on, Engine off, pressurize the fuel rail, turn key off and see how long it takes for the pressure to bleed off. Fast bleed down would indicate fuel pump check valve failure.

If the static test result is within spec, then disconnect the vacuum line from the FPR & plug the vacuum line. Start engine & observe the pressure. If the pressure is low again, then the regulator is at fault.

[frantinoro]

Hey. Static fuel pressure not running was around 45-50, can't remember off the top of my head, but it did decrease when running. When removing the vacuum line while running, the psi also did jump up to around there.

[Paul Workman]

Hey. Static fuel pressure not running was around 45-50, can't remember off the top of my head, but it did decrease when running. When removing the vacuum line while running, the psi also did jump up to around there.

Well, "normal" static pressure with low dynamic pressure speaks to a DELIVERY issue - a blockage somewhere.

First up: FUEL FILTER or fuel lines come to mind. I'd put the pumps and the "Y" and connectors on the back burner for now i.e., not indicated by symptoms, but part of the 'delivery' system.

[frantinoro]

I did it a few months ago; but I'll do it again

[frantinoro]

So I blew out the lines, warrantied my pumps and put another new filter in. Now at WOT I'm getting 50 psi and 40 psi idle. What to test next?

[frantinoro]

To clarify, it's still a little rough at lower rpms, and will not go into full power Mode. I jumped C17 and they opened just fine. No leaks, pump runs every few minutes and I've tested everything under the plenum. Blew smoke into all the hoses going into the plenum and not a single leak, just some smoke coming out of the air filter

[frantinoro]

Any idea what to test next? I hooked up my scanner and the left bank is running lean (BLM iand int Anmrr at around 150)

[Ccmano]

Have you checked for codes? Easy to do with a paper clip if your don’t have a scanner. Electronic issues will usually throw codes.

It’s also possible the accordion air bridge connector between the air filter housing and the air horn is collapsing at full throttle, giving the impression of no secondaries, had it on mine. Remove it and drive it without it in place. If that’s the case you’ll feel the difference immediately.
H
:cheers:

[frantinoro]

Thanks for the reply. The accordion has been replaced with a Jerry's gaskets one. I do have a scanner and it throws no codes, but has thrown a lean code left bank a few times. My BLM and INT on the left side is around 150 as well, and the right side stays around 130. I jumpered all the injectors and heard a click for every one too. Although my scanner is saying the vacuum at idle is 0 kpa, but I'm not sure if the car should be giving me a reading for that. TPS and MAP voltages seem fine. O2 sensors are new and cycling like they should in the scanner, although they do not read evenly, and cycle slightly offset, I could not find anywhere if that was normal.

[Paul Workman]

Any idea what to test next? I hooked up my scanner and the left bank is running lean (BLM iand int Anmrr at around 150)

IF the right side is running LEAN, the scan of O2 sensors would be of interest next.

-the cross counts and the sensor voltage would be go to k ow.

But, the proof can be accomplished too by swapping the O2s right to left & left to right and see if the lean condition follows the respective O2.

Note of concern: high KNOCK counts and burned valves can result from a lean condition. You wouldn't want to be driving it in that condition (lean on one side).

[frantinoro]

I will swap the O2 sensors and see if anything changes. I will also get the cross counts, but afaik I have not noticed any knocks being registered

[frantinoro]

if anyone else has the snap on mt2500 scanner, I'd love to hear if your scanner registers a value for vacuum(kpa) at idle. let me know!

[frantinoro]

So I pulled the plenum, double checked the secondaries and manually fired the injectors, and they're all spraying fine. If I swap the O2 sensors wouldn't that not make a difference when cold? It runs off when cold or warm so I'm stumped. What do I check next?

[grahambehan]

Do you still have the air injection on the car, if so look at the check valves on the manifolds, air leaking there can cause the symptoms you decribe

[frantinoro]

How do I test these check valves?

[frantinoro]

So I swapped O2 sensors, left side still lean. I noticed in open loop the right o2(which was on the left) cycles, while the left does not.

[grahambehan]

So, the sensor , now on rhs is stuck around 450 mg and the sensor on the legs is cycling above and below that value, but still addind fuel to the long term trim.

[frantinoro]

Hi Graham,
Let me clarify. I swapped the sensors with no effect, but In open loop, the left injector doesn't cycle. In closed loop it cycles normally.

[grahambehan]

Ok my # is 260 701 8860, if you wish to discuss

[frantinoro]

So, I took off the air setup, and noticed one seemed to leak slightly when sucking, and had a faint taste of gas. Can I just remove the diverter and connect the two together, or do I need to block them individually to delete the air setup?

[XfireZ51]

So, I took off the air setup, and noticed one seemed to leak slightly when sucking, and had a faint taste of gas. Can I just remove the diverter and connect the two together, or do I need to block them individually to delete the air setup?

If u disable the A.I.R., u also need to tell the ECM u r doing that. So a minor change in the calibration is called for.

[frantinoro]

I was told that this wouldn't affect anything. Either way, I removed the diverter and connected the two together, and it honestly made the right bank more lean, or maybe I'm crazy. I'm open on what to test next. I noticed the cross counts for the left bank were like 10-15, vs the right bank was 0-2.

[richarde]

You said originally that 'I got my zr-1 and it never ran right, but after sitting for a few months it's a lot worse'.
I guess that you purchased it earlier this year. Did you get any history with the car that could point to a resolution? Could it be a mechanical issue that is 'tricking' the sensors?

[frantinoro]

I did not get any history with the car no. I did notice that the INT creeps up ONLY at idle. I changed what I thought was my leaky check valve with a new one and no fix. Although I JUST found out both my resonators are cracked.

[A26B]

I did not get any history with the car no. I did notice that the INT creeps up ONLY at idle. I changed what I thought was my leaky check valve with a new one and no fix. Although I JUST found out both my resonators are cracked.

BOTH??? resonsators Only one resonator (in the middle) & 2 mufflers @ rear. Are you perhaps referring to the catalytic converters, welded into the exhaust manifolds?

[frantinoro]

Hi, yes both. I have a Corsa cat back. I doubt that would cause my issues though. What should I test next? I'm really stumped.

[XfireZ51]

If resonators are leaking they could suck fresh sir into the exhaust which could impact the operation of the O2s.:USFlag:

[frantinoro]

Even though they're like 3 feet downstream?

[XfireZ51]

Even though they're like 3 feet downstream?

Its happened to me with a leak at the muffler. Idle and Decel are two pointa where engine vacuum is at its highest. It can pull fresh air past the O2s creating a “false lean” condition. That in turn will cause the ECM to richen the AFR.

[frantinoro]

Could this be the reason my car feels down on power too?

[XfireZ51]

B4 u can reach any conclusions u need to make certain that the motor is mechanically in order. A leaky exhaust affects how the ECM manages the motor.