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The 97 LT1 is in my off-road truck and recently after being stored for a while the throttle won't advance. I'd be appreciative of any ideas? Video at the link below.
https://youtu.be/6p4sxeKmOiE
I'm also wondering if anyone has any good ideas for a a reasonably priced aftermarket computer and wiring harness that I can connect to a laptop for management?
Welcome to the site. Hope you enjoy your time here.
My first guess woul dbe the throttle position sensor has gone out, but it could also be the connections are bad from setting... There is a test procedure if you have a V.O.M. - google the test and also EFI management systems. It's amazing what you'll find.
And don't forget to do the same searches within YouTube, a lot of videos on these very topics.
Hey Flyer, I don't usually give tech advice, I just come here to read and look at hot rod builds. But in your case, I own three LT1 powered vehicles and have a little bit of experience with them.
After looking at your photos and watching your video a few things stand out.
1) You have a big vacuum leak, indicated by the really high idle speed and the throttle stumble. From the photos it appears your PCV system isn't connected properly. It needs to be plumbed properly. You can find some good photos of the component setups on a site called SHBOX.com. He a great guy who built this gold mine of LT1 information.
The PCV valve should be in the drivers side of the intake manifold with a line running to a fitting under the front of the throttle body which supplies the vacuum. I've got a feeling thats where your leak is. That filter you have in the rear of the passenger side valve cover is a no-no because it's also allowing un-metered air(after the mass air flow sensor) to to enter the engine if your PCV line is hooked up. Any un-metered air entering the engine whether a vacuum leak or improper plumbing will make the PCM think it's running lean and compensate by adding fuel so it's important. Take that filter out and replace with a plastic elbow for a 1/2" line and run a 1/2" rubber line to the crankcase ventilation supply fitting(the top fitting (1/2") on the passenger side of the throttle body). This supply line has already been metered by the MAF sensor so the computer is happy.
2) The inlet to your MAF sensor needs to have a filter on it because even tiny specks of anything will cause it to read wrong.
Remove and clean the MAF sensor with CRC cleaner made for that purpose before you put a filter on it. If possible try to put about 6" of straight hose on the MAF sensor, then the filter. This makes a smooth non-turbulent air stream coming into the MAF sensor which makes them read the flow better.
3) After you fix these items, look over the entire intake for any additional vacuum fittings that might be un-capped. Then check and tighten up all the intake bolts if any are loose.
See if it runs better then let me know. If it runs better then I can direct you to sources for computer tuning if it even requires any.
Thank you 34_40 and Joatmon! After running a test on the TPS, mine appears to be good. I wasn't able to find any bad vacuum lines but perhaps I'm overlooking something? Video below:Quote:
Originally Posted by 34_40
https://www.youtube.com/watch?v=jslZcqJ0Hxk
Can't sleep Denny?????????
This install is pretty well butchered up to be looking for a couple idems that are causing the symthongs-----------what I see that are sorta pointing to multiple potentional problems are rusty header on one side----good looking one on other side-points to exhaust system area as for leaks, O2 sensors,(later systems have 4 sensors), MASS aIRFLOW has no tube/ host on inlet side-they don't read good without it-------
Also California cars had different rules and smog systems----------probably pretty much ignored in this set up---------- is it street driven or strictly off road???
The first thing I would do to sort this out would be add a 2 foot long tube to that mass air flow sensor intake AND also make sure no goo on the sensor-( some off road/race customers have had KN and similar air cleaners blue goo contaminate them)
The MAF is clean. No Goo. Not sure I'd call it butchered but if you say so. Only off road. One of the headers broke and a replacement was installed a while back. No leaks in the exhaust system and O2 sensors are connected. The motor ran great for years with it's existing configuration. It only recently had issues after being stored for six months. I think I'll just start testing all the sensors one by one and go from there. Thanks for the helpful input.
"97 should be OBD 2 which will supply you with some pretty good data. You really need to have the computer scanned and look at real time data to know what is going on, otherwise you are shooting in the dark.
Keith
Thanks Keith, Looks like the person who installed the motor cut some lines to the OBD2 port. Makes me think it's maybe an OBD1 computer using an OBD2 port? I get a "Link Error" when connecting my OBD2 code scanner but the port does power on the scanner which is not self powered. Wondering if there is a way to get the codes with an adapter or wiring diagram? My ECU is Service# 16188051 which I think is from a 95 Camaro. Appreciative if anyone can shed any light on how I can read the diagnostic codes from the ECU. Thank you!
https://i.ibb.co/ng4Pc2w/1.jpg
https://i.ibb.co/zR8P3nb/2.jpg
IIRC------there are 128 terminals on the ecm plus several more on an anti/theft? model (body control)
You need to put a piece of tubing on that MAF control valve to staighten flow to it ( maybe just putting the air cleaner eelement on it will help-
One new header??? does it clear the sparkplug wires good because not many headers clear the angled spark plugs------- Knock sensors installed correctly in the right threaded holes???
SBFlyer. based on the fact that your engine ran great for several years as it's configured I agree with you, I wouldn't see any reason to be concerned with the MAF placement or other sensors either. The fact that it only developed issues after sitting idle for six months? I think you're on the right track to test sensors as you mentioned. Seems like you're likely looking for a corroded rheostat surface or corroded contact points. Denny gave links to a whole bunch of OBD wiring diagrams, and with time you should be able to figure out what those cut wires went to, and if you're dealing with OBDI or II. Wish I could help you with how to pull codes other than using a reader, but I can't. Best of luck with your search.Quote:
Originally Posted by sbflyer
I have a '95 with the LT1 that was a late '94 production car, that I purchased in December of '94, and it's an OBD1. Pretty sure they went to OBD 2 in '96. The ALDL plug you have pictured only has a couple wires that go to it. If you in fact have a '95 that's OBD 1 the pinout is Pin 2 PPL (not used), Pin 4 blk to ground, Pin 5 blk/wht to ground, Pin 6 wht/blk to pin 20 of cavity D of the PCM (diagnostic request), Pin 8 blk/wht to the keyless entry receiver A C1, Pin 9 tan to diagnostic energy reserve module B11, electronic brake module ecm or traction control module A11 C1 and the PCM pin 30 of D cavity, Pin 16 org 12v. Pin 9 of the ALDL is the serial data line to the PCM, EBCM/EBTCM.
Just looked at your picture again and you are missing the tan wire in Pin 9 and the white/black wire in pin 6. Just from looking at the current pinout of the picture, I'm assuming you are running a '95 computer, which would be OBD1. Run a temp or permanent wires from pin 9 of the ALDL to pin 30 of cavity D (plug) of the PCM, and Pin 6 of the ALDL to pin 20 of cavity D (plug) of the PCM and you should be able to read data. Not sure how much data you will be able to read since it's OBD1, but it will get you started. I have all the manuals so I can guide you if you find something. If you need a picture of the wiring schematic diagram I can snap one and upload it tomorrow
Thank you Keith and Rodger! I'm thinking it might make sense to simply buy a used 97 OBD2 ECU and wiring harness on ebay and replace my existing 95 OBD1 ECU? Any reason why that wouldn't work on this LT1 motor? Compatibility issues? Sure would be nice to be able to connect a scan tool to get data and codes.
Nothing wrong with the headers other than one is rusty. They clear the plugs/wires with plenty of room. The air cleaner is on now and no different. I unplugged the MAF while the motor was running and it wanted to stall which makes me think the MAF is working properly.
I'm pretty sure Keith is right. There's a bad ground or corroded wire somewhere that happened while it was in storage. I'm running through all the wiring now using the ECU diagram. Hopefully I'll find it. Really appreciate everyone's input. I'm a software engineer who grew up in a mechanic household so I'm by no means an expert but I catch on pretty quick with this stuff and it's fun!
I believe there is a gang ground on front of the left head, upper bolt that should have a bonding wire and 2 other wires connected to it.
If you install those two wires that are missing from the ALDL to the PCM you will be able to get codes out of it.
Not sure about the compatibility issues if you upgraded to a '97 computer setup. You would have to do some research about that one.
PCM swap for the LT1. All Stuff LT1 related
and you might try disconnecting the battery over night and reconnect it the next day before starting other stuff-------
Disconnect battery to wipe out memory of recent running-
Put on the air cleaner
Clean the O2 sensors
Fresh gas---------if your tank has quite a bit in it now, drain it and refill with whatever brand/octance/ % etonal you will normally be using-------
Don't be winging the throttle for a few seconds like in your U tube vid-
It takes a while for temps to get to normal------
Temps----water/coolants, O2 sensor, inlet air temp-------
if you have a lazer temp gun , check the exhaust header tubes up near the cylinder head to see if all 8 are close or if some are eratic-----
Pay attention to what Jerry tells you or asks you to do---------
Two important things to remember about sensors----------they could be defective and not be sending info, sending the wrong info---OR SENDING THE ACTUAL INFO THE ENGINE IS MAKING !!!!!!!!!!!!!!!!!!!!
IIRC, use to have to do this after any major repair or after it set too long. I ran the throttle up to about 1500 rpm and held it there for a couple minutes until it smoothed out.Quote:
Originally Posted by jerry clayton
Turned out to be a bad IAC. Replaced it and she runs perfect. Appreciative of those who had useful input.