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Hey all,
Long time listener, first time caller here. I bought my dad's '95 Z28 off of him in 2020. He drove the car very little from '03 to '20, so I've gotten used to chasing problems damn near daily (I owned a '97 3.8 Firebird from '17-'20 in my High School years as well). Here is my current dilemma/disagreement with my dad:
The car has been down on power and stumbling/misfiring for about a month now (happens cruising at a constant rpm - hesitant to pick up until I really step on the gas, and even then, it takes some time to pick up and go. There's also an occasional rough idle when sitting at lights). I checked the plugs (they were disgusting) and found I was burning oil pretty badly. I of course knew this already, as I was adding nearly a quart a week at that time. I compression tested every cylinder, and all came back clear. Figuring the leak could have been an intake manifold leak or valve stem leak, I took a gamble and went for the manifold. Sure enough, it was mangled and melted. Replacing it has significantly helped the oil burn, but the misfire was still present (though noticeably better). Turning my attention to the fuel system, I noticed the fuel filter had NEVER been changed (I just rolled over 200k miles). Changing the filter made a world of a difference, and the stumble/misfire is nearly gone, and the power seems to be nearing normal again.
Given how significant the filter change helped, I think I should get the injectors (also all original) serviced. My dad's opinion is that I'm 'throwing money at the issue'. He could well be right, but with as nasty as the old filter was and with how much better the car is running with a new one, I thought my line of thinking was logical.
Looking to you guys who certainly have more experience with these cars than I do. Open to any/all suggestions!
There's a good chance the injectors need service, given the intermittent use of the vehicle. But always good to do basic checks before playing parts replacement roulette. A new set of injectors may not cost a lot more than servicing the old ones.
Then for a power diagnostic tool consider downloading Scan9495, buying a cable, and accessing the PCM data to look for problems. It's possible to run a data log while driving the car under various conditions, particularly those conditions that experience the problems.
I used my buddy's reader to scan for codes, but nothing came up. Now, I'm not sure if that's because no codes were popping, or if it's because the car has an OBD I with an OBD II port, and we were using an OBD II reader.
I did check the fuel pressure - I wanted readings before and after changing the filter (to compare and analyze how much of a difference changing the filter made), but the rental gauge from Auto Zone was faulty without my knowledge. What I thought were low psi readings before the filter turned out to be faulty readings! Got a new gauge and it all checked out. 46psi when priming the pump (my dad has an adjustable FPR set to 46psi), 45-46psi when idling with the FPR vacuum line disconnected, and right around 44psi with the vacuum line connected. After turning the car off the pressure in the gauge seemed relatively constant, leading me to conclude that the pump is strong, the FPR doesn't leak (no fuel in the vacuum line on the FPR), and the injectors aren't leaking (or at least aren't leaking significantly). I'll also note when I did the intake manifold job a few weeks ago, I inspected the injectors and they looked okay (I know, I know, you might not SEE a work injector, but I was just looking for major flaws). I replaced the O-rings and spacers on the injectors at that time as well.
Thank you for the links! Given that the car is in running condition and can get me to work every day, I've actually been considering buying a cable and installing some datalogging software but haven't dedicated the proper time to research it. Your references (and especially the PCM scanning guide) will make the learning curve so much easier! I've read about GaryDoug's Scan9495 along with Steveo's EEHack but only surface level reading.
Moving forward I think I'll but a cable and download some datalogging software. I agree with you - a $60 cable that'll let me diagnose and obsess over every parameter will get me much further than blindly buying new parts Working on updating my signature as well, Fred. There's a lot of work done to the car and a lot of digging through documents I need to do!
You can't pull 1995 codes with an OBD-2 scanner. You need an OBD-1 scanner with the correct 16-pin cable, or a 12-pin to 16-pin adapter, or jumper wires:
OBD-1 scanners are hard to find. There are sometimes used AutoXray units available. Do not buy a cheap $30 box that claims it will read through 1995. It's just a box with a switch that shorts the DLC pins to flash the codes on the SES light. They only work on 1993, nothing newer.
There are dual OBD-1/OBD-2 scanners available. Avoid scanners from Innova and Equus because they have a corrupt database for the LT1 engine, and produce a list of about 7 codes even if you don’t have any codes. Also shows codes that are non-existent.
The fuel pressure should be set to 43.5 PSI with the vacuum compensation line off the regulator. The only exception would be if you installed injectors flow rated at a slightly lower flow rate than the stock injectors (24.9 #/Hr), or if the 383 needs more fuel than the injectors can deliver.
I definitely prefer Scan9495. I never needed scanning software, because I was running an aftermarket ECU that had data logging built in. The EEHack logs seem two cluttered and difficult to manipulate.
PS: the Formula in my signature has been sold. The new owner is happily running 9-second passes. I just “aged out”.
Ahh that would certainly explain why the reader didn't display anything for us. What a joy! Thank you for the tip to avoid Innova and Equus scanners - is there a brand apart from AutoXray you would recommend, or is that the best available in your opinion? I think if I buy a cable, install the datalogging software, and am able to learn how to read the data properly I wouldn't need a scanner anymore, right? I haven't used a datalogger before, but I could imagine it would give me more comprehensive data to analyze than a scanner would. Thank you again for your input comparing Scan9495 and EEHack.
Hmm, I recall the fuel pressure reading above 43.5 with the vacuum compensation line off the regulator. The injectors are totally stock, so I'm curious to know if you're right about the 383 needing more fuel than the injectors can deliver. I've read some conflicting opinions on the forums regarding injector setups. My dad actually purchased Racetronix 32 lb/hr injectors back in the day, but never installed them on the car. I actually have them brand new in the bag! I briefly considered replacing the current OE injectors with those, but I have a few hang-ups with that:
1. If the stumble is not injector related, then I would just be putting nice new injectors into a flawed system.
2. I'm not sure how far the stock (all original 200k mile old) fuel pump will take me. If the 32# injectors require more than that old pump can give me, then I would be looking at getting a new pump at that point.
3. My third and final concern is that I have no way to know if they would make a difference or not! I don't know if the O2 sensors would account for the flowrate from the new injectors, or if I would have to flash the ECU (I think that's the correct terminology - I have no experience tuning) to tell the ECU how to adjust to account for them.
That third and final point is what's leading me down the datalogging rabbit hole. Data analysis is in my blood, and I would very much love to learn to read that information to help me make a more informed decision as opposed to reading conflicting opinions on forums (that's no slight to you by the way, you've been very helpful! I'm certain you've been around enough to know what I mean - 70,000+ posts, wow!).
P.S: 9 second runs are solid! I think I've got some old slips from when my dad dragged my car back in the early 2000's before he did the 383, and if I recall correctly, he was in the 13's. I mention the signature because I saw your post in the newcomer's page! I think I'll be a pretty regular member of the forums here. Not looking for a quick and dirty "it's the injector on cylinder 5" response from you guys
A lot of people seem to like Actron. I have an OBD-2 Actron. Reliable brands seem to be OTC, Bosch, SnapOn, even some cheap Chinese Tech2 clones. OTC makes the GM tools, including the Tech2, but the genuine Tech2 “basic kit” is $4,000.
We aren’t certain that Innova/Equus (apparently both made by same manufacturer) are all a problem. I think the one people have had trouble with is a 31xx model (can’t remember the exact number). I'm helping someone on another site like this with a 51xx series Innova. He indicated last time he scanned he got “8 or 9” codes, But he didn’t write them down, so I asked him to run another scan and let me know what shows up.
An advantage of Scan9495 is the fact that the author, GaryDoug is a member here. He's able to help with install and communication issues. He's also the one who tracked down the Innova issues.
When you finally do a scan, and find a code, do not blindly accept the scanner's definition of the code. Best thing to do is look up the codes in the 1995 factory service manual. Free download, courtesy of Gary:
Ahh, I see what you mean not knowing if Innova/Equus are the problem or not. I wonder what would cause them to throw so many codes...
Even when the scanner gives you codes, the data from the Scan9495 would still be helpful to define why that code is being thrown, right? I think my plan moving forward is to buy a cable, download the software, and get familiar reading the data. I read your "LT1 PCM Scanning-R2" document last night and it read very clear to me (I've got to dig up my ICE notes from college to refamiliarize myself with everything!). If I run into trouble with the Scan9495 software, what would be the best way for me to reach GaryDoug?
I have several factory manuals courtesy of my dad! I'm also fortunately very familiar with Rob's Shbox pages. So far much of the work I've done on the car has been maintenance related, so I'm a frequent user of his 'How To's' and 'Reference Guide'.
As a side note, I mentioned joining the forum to my dad last night (he was right about me throwing money at it after all), and he asked who was giving me advice on here. He actually remembers you specifically from surfing the forums back in the day! Only had good things to say about you and your systematic thought process. We're both very appreciative you're still around!
The Actron CP9690 is their current product that does OBD1 and 2. It's not real cheap and a little hard to find. It supersedes the CP9185 and CP9190. You might be able to find one of the older models if you need a hand held device (or you can get an old OBD1 scanner and adapt the connector like shown on my site). Doug's software would be a good solution if you want to be educated on the operational parameters (always a good idea, IMO).
Thank you for your input! I actually have read your connector adaptor instructions on your site (I feel like I'm reading something new on your site every day, actually - incredibly helpful), but as quick and helpful as pulling codes might be, I think I might shoot straight for the Scan9495 software and get comfortable reading it.
I've taken courses detailing engine function and optimization, and of course became very familiar with the basics. It was a huge interest of mine, but the lack of hands-on experience prevented me from really getting into the nitty gritty of it. I can only do math for so long before I need to get my hands dirty and go fast! (I guess that's the impatient youthfulness in me showing). I'd like to take this opportunity (that being the occasional stumble/misfire) and use it to better my understanding and get this car running the way my dad had it in the early 2000's.
I'll order the cable today and install the Scan9495 software tomorrow (off Friday). I'll be sure to keep you guys posted and bump this thread when there are updates/results!
Click on the individual's screen name and the dropdown offers option for "private message" or "email". Another option is to type the "@" symbol, immediately followed by the member's screen name. He will receive a message indicating someone has called him out. And, if I see anyone struggling with Scan9495, I will contact him and ask him to take a look.
I can look at the data and interpret it, but I know nothing about installing the software or actually using Scan9495. 25 years ago I used lt1_edit and pcmcomm with the stock PCM, but in 2000 I installed a MoTeC aftermarket engine management system. That allowed for tuning and data logging.
When I still had the factory PCM I purchased a "Scanmaster LT1". That connected to the data wire in the DLC and displayed about 2 dozen different sensors and PCM parameters, one at a time. It also displayed any codes. I mounted it on top of the steering column. Just watching that data and spending some time studying a book "How to Tune & Modify Chevrolet Fuel Injection", Ben Watson, Motorsports International, ISBN 0-7603-0422-X helped me figure out how it all worked. My scanning guide was developed from that experience.
At some point, you have to provide as many details as you can about the engine and transmission modifications. I don't need any other mod - suspension, appearance, etc., just the things that will alter the data and the relationships between individual data items.
Fantastic! Thank you! If I run into any issues, I'll be sure to post them. I'll post my results too once I have an understanding of them.
Oh, I'm familiar with MoTeC! I was the Vice President of Florida Tech's SAE team, and we used their ECU's on our Formula car. I never worked directly with it, but I know the team was successful in tuning with it.
I would like to keep the factory PCM (I'm trying to keep the car more or less exactly how my dad had it), so the Scanmaster LT1 is intriguing to me. Does that log any of the data or does it only display it live? I'll earmark that book - it could help me learn the basics in addition to your scanning guide, and also if I decide I want to look at larger injectors down the line. (My dad bought larger injectors and intended to swap them on, so installing them still counts as keeping the car how my dad had it!).
I have a solid maintenance log and lots of old records/receipts to dig through from my dad. I'm unfamiliar with much of the work done to the motor, but I did a full transmission rebuild myself, and have prior experiences working on T-56's. Apart from a reverse lockout delete and a slight upgrade to billet shifter keys, the transmission is OEM. The differential hasn't been modified at all, and I have the original wheels still, so those parameters should all hold the same values as from factory. I do know there's an aftermarket camshaft in there, and self -aligning (?) rocker arms. That means he must have done a valvetrain workup at some point, so I'll see if I can dig up some more detailed information. When I do, I'll be sure to add it to my signature!
08-02-2023 | 09:03 AM
Working on updating my signature as well, Fred. There's a lot of work done to the car and a lot of digging through documents I need to do!
