1991 ZR1 ODB1 Port Location-Diagnosing Rough Running ZR1
 

A new 1991 ZR1 owner here, I have a few questions (yes, I did try the search button :)

Where is the ODB1 port located? I did not see it under the driver's side dash. Do I nee to remove any panels to get to it?
Which USB cable do I need to read codes using my lap top?

Very rough running car here...

Thanks!

Re: 1991 ZR1 ODB1 Port Location
 

if the 91 is the same as the 90, and I think they are, it's about half way down the interior colored panel that's by your knees and it has a black plastic cover on it that pops off. I don't have any softwear to read codes, just gordons plugs, but i'm sure someone will tell you what they use shortly.

Welcome to the forum. What seems to be wrong with your car?

Re: 1991 ZR1 ODB1 Port Location
 

It would not be unusual to find the ALDL connector stuffed up behind the drivers side hush panel. If the cover "Diagnostic Connection" is missing there would only be the connector visible and it's mounted towards the rear edge of the drivers side hush panel right of the column. It could easily be overlooked I'd guess if you didn't know where you were looking.

In this post you can see it's approximate location to the hush panel edge. It's a tough find for many:

http://www.zr1.net/forum/showpost.ph...95&postcount=1

Re: 1991 ZR1 ODB1 Port Location
 

Welcome onto the boards there.

If reading codes is the only objective, you can get it done with a paper clip (once you find the ALDL interface).

But scan software IS something good to have...

Cliff [Dynomite] will post a link for eBay cable listings, for laptop-to-ALDL connector.

I use this one from Moates:

https://lh6.googleusercontent.com/-j...0/IMG_5608.JPG

Re: 1991 ZR1 ODB1 Port Location
 

Thank you for all the responses!

I thought I looked pretty thoroughly, but will try again.
I just picked up the car (539) from Arkansas and drove it home to Chicago. The car was running slightly rough when I picked it up, but 100 miles in to ~700 mile trip it started to misfire badly with the check engine light periodically coming on. It limped the rest of the way home.

I had no choice, but to drive it the rest of the way, hopefully no damage resulted from that.

Another thing I noticed was the oil pressure gauge being always pegged to the max in the lower gears.

Currently my ZR1 has the power of a poorly tuned Chevette. :(

I found couple of vacuum hoses loose (MAP and pressure regulator), I also replaced PCV check valve assembly hoses with ones from jerrygaskets. It and the felt much better at first, but after a short test drive it reverted back to a bad misfire and shake.

So this is where I am now…
So ’91 ZR1 has a 12 pin ODB1 connector?

This one right?
https://www.moates.net/aldu1-and-cab....html?cPath=64


Thanks again!

Re: 1991 ZR1 ODB1 Port Location
 

There are enough of us here in Chicagoland to straighten the car out.
Welcome to the FBI.

Re: 1991 ZR1 ODB1 Port Location
 

In order of likelyhood the usual cast of characters that will cause a "Badly Tuned Chevette" syndrome are:

- Fuel injectors
- Coil packs
- spark plugs/wires
- Fuel pumps

If the fuel injectors are original, they are the most likely culprit.

Get one of the FBI (Fast Boys of Illinois) to pop over for a quick diagnosis, it will save you time, trouble and money.

'Crabs

Re: 1991 ZR1 ODB1 Port Location
 

Yep.....just tell us about how many miles on your ZR-1.........But as Crabs suggests.....start with Injectors :thumbsup:

Low Mileage ZR-1 Restoration (Audio, Injectors, Starter, Clutch Hydraulics)

Re: 1991 ZR1 ODB1 Port Location
 

If the injectors are original, replace them even if the problem turns out to be something else- they are gonna give you trouble- guaranteed.

probably if it kind of runs ok cold and then misses bad as it warms up- yeah, that's injectors.

Re: 1991 ZR1 ODB1 Port Location
 

~56,000. If I will be going through the trouble of pulling of the intake
I might as well also do the rest as suggested?

- Fuel injectors
- Coil packs
- spark plugs/wires
- Fuel pumps
- secondary solenoid
Anything else? Would like to remove as much emmissions related mess as I can (really don't want to pull the heads)

Re: 1991 ZR1 ODB1 Port Location
 

Where in Chicagoland are you located?

I sure one of us is near you to help

Re: 1991 ZR1 ODB1 Port Location
 

FBI to the HP rescue, brotherhood

Re: 1991 ZR1 ODB1 Port Location
 

If you're going to bulk replace parts might as well hit the O2 sensors.
If it were me I'd clear the codes then go for a drive until a code sets then dump the codes and find out what's wrong and go at the codes in the order the come out. The exception would be injectors if they are OEM. They need to come out as was mentioned.

Re: 1991 ZR1 ODB1 Port Location
 

If it is running, I would not change parts just to change them. Injector failure is inevitable so change them. But I would try to ohm the plug wires, unless original appearance doesn't matter to you. Also read the threads ondiagnosing the coil packs. If you make wholesale changes, you may never identify the root cause. Change one thing at a time. Even if you change out a good part you can keep the known good parts as spares. You are in Chicago, no better place for a ZR-1. Plenty of help in that neck of the woods, and some real professionals.

Good Luck
David

Re: 1991 ZR1 ODB1 Port Location
 

he may not know about injectors being new or old
he can test them
http://www.zr1specialist.com/HAT%20W...in%20Place.pdf

Re: 1991 ZR1 ODB1 Port Location
 

Thanks again guys. I'm in 60091.

Re: 1991 ZR1 ODB1 Port Location
 

Fully Automatic Assault Wallet repair technique never works. Buy parts, and Plug n Pray :thumbsdown:

Re: 1991 ZR1 ODB1 Port Location
 

That was not the intent. As long as I was going to remove the plenum anyways I might as well replace the parts that are difficult to access and are prone to failing. I fully intend to diagnose and have already ordered the ODB1 usb cable and module.

Re: 1991 ZR1 ODB1 Port Location
 

This is actually what I did. Not interested in pulling plenum, then need to pull again or on a piecemeal basis.

Re: 1991 ZR1 ODB1 Port Location
 

There are several nearby you. Al at Brakes Plus is nearby Golf Mill. Pete is in DesPlaines and Bob banks is up in Lake Bluff.

Re: 1991 ZR1 ODB1 Port Location
 

The plan for today is to replace the spark plugs and recheck for vacuum leaks...

Looked at couple of the plugs. The first looked OK, but the second looked pretty sooty. The spark looked strong. Injectors seem like a likely culprit.


https://y6dvja.dm2302.livefilestore....141.jpg?psid=1

https://y6dvja.dm1.livefilestore.com...420.jpg?psid=1

Re: 1991 ZR1 ODB1 Port Location
 

Forgot to mention - Last owner had a Doug Rippee Performance chip installed. I'm not familiar with that tuner. I wonder if it would be worthwhile to go back to the stock chip that came with the purchase....?

Re: 1991 ZR1 ODB1 Port Location
 

Some of the sootiness may be due to the issues you described when you first got the car. I would get new plugs and take a look after a few drives. If you can do a scan, see where the BLMs are.

Re: 1991 ZR1 ODB1 Port Location
 

What does BLM stand for?

Re: 1991 ZR1 ODB1 Port Location
 

Block Learn Multiplier. It is active in Closed Loop. At 128, it means the ECM is making no change to the base fuel map. So a scantool will tell you if you're running rich or lean and where.

Re: 1991 ZR1 ODB1 Port Location
 

No luck after replacing the plugs
Did the paper clip diagnostic:
http://youtu.be/tl7aOi9GetY

From what I could tell:
31 - Cam Sensor Missing or Too Many Pulses
33 - MAP Sensor Voltage High
44 - Oxygen Sensor (Left Bank Lean)
55 - Fuel Monitor Lean
64 - Right Oxygen Sensor (Right Bank Lean)
66 - ??

Looks like a mess?

Re: 1991 ZR1 ODB1 Port Location
 

When you have multiple MALF codes like this, first place to look is making sure the memcal is seated properly. Also, disconnect the BATT and erase. These may all be in history. Make sure to see if they come back, ie CEL again.
Also, make certain the ECM ground is in good shape. I hope you have an FSM.

Re: 1991 ZR1 ODB1 Port Location
 

I did reseat the chip. Disconnected the battery, then went for a 50 mile drive. No codes, but still running like crap.:mad:

What is the part number of manual? I do have a ZR1 supplement.

Went for another drive and it threw 55. Fuel pressure?

Re: 1991 ZR1 ODB1 Port Location
 

I would say to ohm out the injector harness. There's a link to the how-to somewhere- It will take about an hour, but you can meter out the injector resistance to find the worst injectors. If you even have one bad one, plan on doing that for sure. It sounds like one other thing might be wrong as well.

One bad O2 sensor on one bank will also cause issues...it would save a ton of time if you can meet up with somebody with a laptop program or the factory tech1 scanner to look at operating parameters real-time when the engine is running- not just reading code history.

Re: 1991 ZR1 ODB1 Port Location
 

Fuel pump(s)?. At least the other codes didn't come back.:flag2:

Re: 1991 ZR1 ODB1 Port Location
 

I guess I will be ordering the fuel pressure tester, already have ODB1 module on order.

Re: 1991 ZR1 ODB1 Port Location
 

While you have the plenum off take a look at the secondary solenoid,a replacement can be made to work from a different G.M. application not sure exactly what at the moment.Another thing you might want to do is before you bolt the plenum back up get out Marc Haibecks DVD on an under plenum systems check.It will show you how to power up the system and check all the secondary hardware in operation.

Re: 1991 ZR1 ODB1 Port Location
 

Fuel pressure was OK, ordered injectors....

Re: 1991 ZR1 ODB1 Port Location
 

I just received my Moates cable and module. What software are you using?

Re: 1991 ZR1 ODB1 Port Location
 

I just finished installing the new injectors. That was what was causing the problem. Thanks again for all your replies.