A serious problem

[8upZR1]

I have a serious problem with my 90. People who have read this forum know how F'd my car is. If anyone has any ideas I would love for you to share them with me. The car starts, but does not idle. If you just hold the rpms above 1000 it runs roughly. Throttle response is absolutely miserable. As I accelerate from a stop the car has not enough torque to get going. I have to stab at the clutch a little to get the car moving. Once moving it feels alright from 1500 rpm till about 2200 rpm. Then it feels like it has hit a brick wall, I press the throttle all the way down at this point and the car slowly accelerates with much effort. Once I hit about 3000 rpm the car comes alive and runs smoothly, throttle response is great, and the acceleration is excellent, but then at around 5,000 rpm the party is over, and by 5500 rpm the motor feels like I have hit a 2 step rev limit. I get deeper into the gas and the motor just starts popping and wont go past 5500 rpm.

I have no fault codes, everything looks good. Most sensors and components dealing with engine/injection have been recently replaced. I have been swapping between factory and haibec chips. Not that much difference. One notable thing was that the factory chip would sometimes let the car idle with the A/C off at 900 rpm, very steady. Then I would turn on the A/C and the rpms would crash.

When I first got the car I remember that it would run like total crap, just like it does now, but only very intermittently. Maybe once every couple of days for a few minutes. Back then I noticed that it seemed to never do it when the car was hot but it would do it when cold. Now it is just constant. Turning the full engine power key off makes no difference.

For a while I had a short runner intake on the car and I thought that was contributing to the torque/throttle response problem so I swapped to a factory unit. It helped a tiny bit but while I could feel some improvement I could also feel this underlying problem.

Today I was playiong with the car and at one point I hopped in and started the car and it felt awesome. I pulled it out of the driveway and it felt great, but then I noticed the SES light was blinking at me. I then realized I still had the pins connected on the ALDL to get the trouble codes. I didn't know if driving the car with the pins jumped was bad so I pulled the paper clip and it ran like crap again. Can I drive the car with the pins jumped? Can I hurt something by doing this? If anyone has suggestions I would be greatful.

[Belsy]

Try basics to see: pull & clean IAC, I use ethyr which drys fast and blows hard. Clean throttle plates, run w/ no filter briefly, may be starving for air?? Could Cats be clogged?? Could there be an exhaust restriction?? Vacuum hoses OK?? All hoses on?? These thing usually won't throw codes!! Good luck=D>

[8upZR1]

No cats, filters good, cleaned the IAC yesterday. ?????? is all I can do.

[Jagdpanzer]

How does the fuel rail pressure look during all this?

[A26B]

I'm a little confused with the "short runner intake." What exactly is that?

Your problem, being intermittent and worsening, sounds to me like an electrical issue. Loose connection, bad ground(s) or open/short in the harness. Part of it sound like it's restricted to closed loop except that once you reach 5000rpm it craps out again. If it were O2 sensors, you should have a code, same as with any other sensor.

I'm leaning towards a bent pin on the ignition module (easy to do) or bad ground(s). If you could data log, you might be able to chase it down.

If you have acess to another known good ECM, I would suggest trying that too.

[8upZR1]

The fuel pressure is constant at around 40 psi and then when I give it throttle it goes up to the 50's maybe low 60's. At WOT with the haibec chip my A/F meter says rich, with the GM chip it is closer to stoich, but still on the rich side. The problem is no longer intermittent, now it is a full time affair. I have tried swapping ecu's, no luck. I was thinking that maybe it is the wiring harness or a pin connection. As of yet I have found none. In the past I have looked at the igntion module to ECU connection but everything looks good and all wires are sending good signals as far as I can tell. I plan on checking this connection carefully tomorrow. Maybe I will find something.

[8upZR1]

The short runner intake was made for me by a friend of mine. It uses a factory plenum and the runner sections are cut away from either side. Then new flanges were cut from 1.5'' aluminum on a water jet and given proper 3/4'' radius inlets. These were then port matched to the injector housings. The roof of the factory plenum was extended outward a few inches beyond the injector housings. Then a new floor was made and it was all welded up with stand pipes in place where the bolt holes need to be. The new plenum covers most of the coolant lines on the side of the motor. This intake is fairly radical for a street ZR1 with 350CID. Maybe when I go to the strip one day I will put it back on. It would probably do wonders for a 415. The runner length of the plenum becomes a straight 1.5'' with no turns and the plenum volume nearly doubles. If anyoine is interested maybe something could be arranged. I have some pics of pre assembled parts. Once I get my camera back I will take some pics of the final intake and post them. One bad thing though is that a factory intake is required for butchery. Or perhaps a 2nd gen model could have a fabricated plenum. Who Knows.

[A26B]

I would like to see some pictures. SOunds really interesting...

[guinnessdood]

Sounds a whole lot like a DIS module problem. Swap in a spare if you have one...if not...Marc Haibeck can loan you one.

[tomtom72]

I'm just a hack but I think if you can drive the car with a scanner plugged into the data port....what's the difference if just the pins are jumped?...I would think to the EEC system there is no difference. How would the system know if a scanner was attached or if the pins were just jumped?

JMHO
Tom:redface:

[8upZR1]

What type of scanner is this and where can I get one? Does the ECU run in its normal fashion when the pins are jumped? No one has posted that this will surely fry an ECU so I may do some extensive testing today, driving with the pins jumped.

I will post pics of the manifold as soon as I can. Hopefully I can do some dyno testing when the car runs right. My neighbor owns a dyno shop and will let me get a full day for $125. Can't beat that.

I have replacement components for most ignition pieces. Swapping pieces has not been fruitful so far. I have an MSD box hooked up. It has an indicator that blinks according to various problems and it says that the ignition is operating properly, for what it is worth. MSD supplies a plug for the harness so you can convert back to stock by simply unplugging the box and plugging in this plug. I do this with no result.

[We Gone]

I'm just a hack but I think if you can drive the car with a scanner plugged into the data port....what's the difference if just the pins are jumped?...I would think to the EEC system there is no difference. How would the system know if a scanner was attached or if the pins were just jumped?

JMHO
Tom:redface:

I have to agree you need to hook it up to a scan tool at this point...Not sure where you are in GA but a buddy of mine in Fayetteville has a shop and does have a Snap-on scan tool..You may want to give him a call and see what he would charge to run a few tests.. he does know ZR-1s and has done a lot of work on them..

John @ Corvette Country 770-461-5211

Steve

[gbrtng]

I'm a little confused with the "short runner intake." What exactly is that?

Your problem, being intermittent and worsening, sounds to me like an electrical issue. Loose connection, bad ground(s) or open/short in the harness. Part of it sound like it's restricted to closed loop except that once you reach 5000rpm it craps out again. If it were O2 sensors, you should have a code, same as with any other sensor.

I'm leaning towards a bent pin on the ignition module (easy to do) or bad ground(s). If you could data log, you might be able to chase it down.

If you have acess to another known good ECM, I would suggest trying that too.

I agree on the ECM - if it's flakey there's no telling what weirdness
can occur. You might not be able to log data either.

I fought with similar problems on my wife's L98 a few
years ago. That one would throw random SES codes which made
think it was a bad ground or related connector problems. Ran like
new with a good ECM.

Glenn
91-1341 and 91-9405

[tomtom72]

I bought a used snap-on MT-2500 scanner. I sometimes use it when I drive just to see what the ECM sees from the sensors. I know for sure that the guys that do "data logging" use software programs that let you hook up a laptop to the ALDL port and drive & record the data for play back later so you can study it. I'm not too swift on this 'puter stuff so all I know is there is a soft ware that you can buy, a cable to plug the laptop into the ALDL, and you can either use it on a dyno or you can do "street tunning" by logging the data(recording the data on the hard drive(?)) & look at it later.

Sorry that's all I know about this stuff.:redface:

A thought just hit me: If the scanner is plugged into the ALDL maybe it is just reading the data flow? Maybe if you use a "jumper" you are putting the ECM into test mode??? I know that I use my scanner to do the KOEO readings and I can start the car & watch as the data changes as the car goes from "open loop" to "closed loop". Stupid Q from me: you know that the ECM is good? If not sure I have a spare ECM with a 90 EPROM in it I could send to you to test if you think that would be of any use?:o

:cheers:
Tom

[Z Factor]

An option since you live in Georgia is to contact Aaron at SGC;

http://www.sgvette.com/

Let us know how things work out

:cheers:

[8upZR1]

I have two ECU's and three chips but no combo seems to solve the issue. There are some noticeable driving differences between the chips as there should be but nothing significant. I drove a little with the pins jumped and it didn't make a difference. I am going to look into one of these scanners. Maybe that will lead to some insight. I did a quick diagnostic with a voltmeter of the ignition module test port and everything seems ok. An oscilloscope would probably be the better test equipment but I do not have one. The Ref high, ref low, EST out, tach out, bypass line all look good before and after cranking.

[368zr1]

If you have the stock fuel injectors (Multec) they could be
causing your strange problems. If they are the original injectors, try ohming the coils out when hot and cold. Should be around 16 ohms.

[Gunny]

Aside from checking the obvious which it sounds like you've already done ...

1) vacuum leaks can do some nasty things with the proper running ... and even when you think you have them all, another one can creep into the equation.
2) someone mentioned cleaning the IAC ... I recently had issues with the IAC and even tho I cleaned it and thought it was OK, 98% of my problems went away with a new IAC. btw, prices for that sensor range from over $100 down to $39 or so from AutoZone. It's usually in stock.
3) another suggestion was to check your injectors ... I think that might be a good place to look very carefully. If you've got a couple of primaries and 2-3 secondaries not working, it might explain some of your symptoms.

Good luck on finding/fixing ... it will be worth it for sure.

I see that you live in the Savannah area ... I'm about 100 miles from you ... my schedule at the moment prevents me from driving down & taking a look, but keep us posted on your progress. I know that you'll get a ton of help here and you will get the beast running properly.

George Jones
Waynesboro, GA
1990 ZR-1
visit my site (http://www.zrwon.com)

[8upZR1]

I had checked the injectors a while back when bad hydraulic lifters kept the motor from starting. Back then they were good. The primaries are original, the secondaries are RC. I guess I will go back and recheck all of the injectors and sensors and their connections. I have not checked vacuum recently either but I am certain it is good. The fuel pressure spikes when you tip in the throttle so some vacuum is definetely present. I will have to check this as well. If only I had an extra 10 hours a day.