i have a sensor or ignition problem. when i set the base timing correctly and leave the dist. computer wire unplugged the car runs OK, but if i turn the car off clear the computer and plug the dist. comp. wire in, then it stumbles and runs like crap and doesn't seem to get any better. i have had this problem for some time so i replaced the dist. cap, rotor, ecm module, coil, plugs, computer, and nothing has seemed to have helped. what should i check next?

wire unplugged = runs OK, but no advance
wire plugged in = runs crappy

thanks in advance for any help!

 

sorry i'm a ASME certified pipe welder, not a GM Tech or i'd take a guess at it.

------------------
ICON Motorsports

1st & 3rd
MM Black Diamond 538 F&AM

 

...and I'm just a dopey electrical engineer, or I'd try it, too...

------------------
Later,
Vader
------------------
"What a Day..."
Adobe Acrobat Reader

 

i am a chevy tech, but your lacking info needed to solve this so i won't bother either.

 

ok, I'll bite. Some information does seem to be missing here, such as, what was it running like before you attempted to set the timing? And does it really run alright with the wire disconnected or have you not driven it yet? Try backing your initial timing off about 10-15* and then see if it cleans up. Maybe you have the base timing way too far advanced.

------------------
'84Z28/'92 305TPI
'92 complete rear suspension/PBR disc/Posi/3:42
Light weight 34.5mm stabilizer bar in front ($10 from wrecking yard)/
"wonder Bar" ($5 from wrecking yard)
23mm sta. bar in rear
Rear RS Springs (slightly softer than my Z28)
comp cam, flowmaster
TB coolantbypass/shutoff valve to heater core
powersteering cooler lines (liberated from another wrecked car of course)
MAT relocated
Ram-Air(home-made) gutted air-box
IROC ground effects/wheels GY245/50's
700R4 superior shift kit/ corvette servo(excellent shift kit btw)
home-made strut tower brace (cost $6)

Rebuilt engine and transplanted it myself.

Love this engine!

freshly painted OCT. 2000 Teal with two white stripes on the hood and deck lid

LOW performance people should drive low performance vehicles!

 

that still isn't the way to diagnose it. is there any advance once you plug it in? how much? is it steady? is the knock sensor picking up knock? replacing parts is not the way to chase down a problem. alot more to solving a problem than guessing.

 

I'm a technition in training so I guess I'm not qualified to answer either.

 

You all are harsh....

It sounds like to me the reluctor wheel is cracked or lost its magnetism. The reluctor wheel (before you ask) is part of the distributer shaft, and must be replaced as a whole distributer. I'm not telling you to replace it, but thats what it sounds like.

I would at least take the rotor off, and look at the "star" looking wheel and make sure it isn't cracked or broken. Its inside the pickup coil, underneath the rotor.

------------------
If you live in Southeastern US, check us out!
South East Thirdgen

GM Master Tech
ASE Master Tech + L1
Savannah, GA

'87 Trans Am
S/D TPI retrofit including functional PassKey,
22# injectors,
Whatever chip I feel like burning,
JET AFPR, Ported Plenum,
TB Coolant Bypass, Custom Cold Air,
SSM SFC, KYB Shocks, Boxed LCAs, Wonder Bar,
8mm Accel wires,
Flowmaster Exhaust,
16" GTA rims,
Corvette Servo,
3.73 Posi
4wheel Disc Brakes

'97 Bonneville SSE

 

Maybe, but you can only preach so many times....

Thanks for helping him out, though. The rest of us weren't qualified. Actually, neither were you - he didn't ask for a MASTER Tech!

Get the new server set up yet?

------------------
Later,
Vader
------------------
"What a Day..."
Adobe Acrobat Reader

 

What is the timing at with the ecm hooked up? What is your initial timing? Do you have access to a scanner? Throwing parts at it is not te way to go about fixing the problem.

------------------
82 z28 350cid, vortec heads, comp 262h cam, Holley 600cfm carb, 2in twice pipes, MSD ignition, turbo 350 trans, 3.73 posi, manly b&m megashifter

 

I had the same exact problem but since i'm not gm tech I can't help...

But man, was it a doozey to fix

Mike

------------------
1989 RS.. Newly installed 350,bored out 30 over, Hypereutectic pistons, double roller cam, double roller timing chain, accel wires, blue streak cap and rotor, rapidfire plugs, chevy caprice 350 chip, 200* fan switch, 3 angle valve job.

[This message has been edited by burntblues (edited May 03, 2001).]

 

Sorry, Just some College kid.



------------------
60 Ranchero - Project ( Money Hole )
85 Sport Coupe LG4 - Daily Driver
Reader's ride -> My Ride

Just another Hot Rod kid, or thats what they all tell me.
Livin' the Stereotype

 

for those of you helpful enough to post a reply that could possibly help i really appreciate it. i've set the base timing anywhere from 8-10* and have been driving it with the computer wire disconnected but i'm not getting any advance = crappy gas mileage and performance; although it's a lot better than with the wire plugged in. if i plug the wire in i do get advance and retard, sometimes good most of the time way off from where it should be. this only happens when i start her up with the wire plugged in. if i start her up with the wire disconnected and then plug the wire in, it runs fine. what's going on? i was thinking the ecu is getting a reading from a bad sensor at startup? check the distrib. and there are no cracks and everything looks OK under the cap. this has been an on going problem since taking ownership.

 

You really dont the idea these guys are trying to convey for you, are ya ? lol

If you ask specifically for a "gm tech" that pretty much counts 99% of the people on this board out. If you just post your question in a NORMAL way, w/out asking for specific people or job professions, then maybe people will help you.

------------------
92 Z28 5.7
------------------
Trick Flow 23° heads, Comp Cams XR270HR-10 cam, Accel intake base + ported TPI,
TES headers, Flowmaster catback, MSD ignition, #24 SVO injectors, 1LE aluminum driveshaft.

Click here to see pics of my car.
Check out our car club Truspeed
Check out the Bin Archive for all your .bin needs

 

sorry for stepping on ya toes all. i was just trying to get the attention of someone who has worked on problems such as this before, such as a gm tech. i had posted this problem several times in the past and still haven't found a resolution. or anyone who can tell me what to look at next??? politics, gotta love it!

 

speeddevil, no ill will was meant to be directed towards you, it's just an on going thing here for people to ask for someone by name, or in your case a gm tech when very few are gm techs. there is an unlimited amount of talent here. our members have done just about anything you can think of to their cars. there are a few of us(moderators and members alike) that spend a great amount of time here answering questions. often answering the same thing we answered last week. good luck with your problem.

------------------
ICON Motorsports

1st & 3rd
MM Black Diamond 538 F&AM

 

ok, ok i get the problem with the subject line i posted. next, i have searched the archives and find many problems similar to the one i have but can not find a resolution posted and there are many suggestions that do not really make sense. i'm not a technician but i play one in the backyard. i'm just looking for testing procedures for the sensors that may be causing this problem. if the ecm wire is plugged in and it's advancing and retarding the dist. wrong then i would think there would be a problem with the esc module or the sensor in front of it but how can i test it?

 

Did you pull the rotor off? You almost have to dissasemble the distributer to see what I'm talking about. I know I may sound buggy or stubborn, but it sounds so much like the typical distributer problems.

It doesn't sound fuel related, because usually, fuel problems will be evident w/ or w/o the bypass wire unplugged. I would definatly say ignition.


------------------
If you live in Southeastern US, check us out!
South East Thirdgen

GM Master Tech
ASE Master Tech + L1
Savannah, GA

'87 Trans Am
S/D TPI retrofit including functional PassKey,
22# injectors,
Whatever chip I feel like burning,
JET AFPR, Ported Plenum,
TB Coolant Bypass, Custom Cold Air,
SSM SFC, KYB Shocks, Boxed LCAs, Wonder Bar,
8mm Accel wires,
Flowmaster Exhaust,
16" GTA rims,
Corvette Servo,
3.73 Posi
4wheel Disc Brakes

'97 Bonneville SSE

[This message has been edited by GMTech (edited May 07, 2001).]

 

when i replaced the spark control module, rotor & cap a couple weeks ago i totally disassembled the distributor and it looked good. i had the problem before replacing those components. i also replaced all my vaccuum lines to make sure i didn't have a vaccuum leak somewhere. ???????

 

does anyone know where i can get a sensor troubleshooting guide from? i know this is sensor related but i'm not sure which one or how to test each one. i have a multimeter, just need something to compare my readings against to determine which sensor may be bad...replacing good parts is getting expensive!

 

lol, i just realized, here we are 20 deep in this thread, and you didn't even tell us what engine/computer we are troubleshooting here.

To answer your last question, there is realy not much you can do to check sensors in your backyard. TPS, MAP, VAC, and BARO sensors are all pots, meaning variable resistance on the output relative to the ends. CTS is a thermistor, it changes resistance with temp. If it's a MAF car, the output of that varies with year, but you need a scope and knowledge to check it anyway.

But really i'm stumped and have no useful input. If it is a MAF car, is it possible that the MAF is bad, but it runs OK w/o the timing connector plugged in cuz it ignores the bad MAF when it isn't getting reference pulses.

What is really funny is you are getting answers from a GM tech, ad all you can say is that it looked good last time you had it apart, but were you necessarily looking at what he is telling you to check. In your situation i think you either follow the advice of the pro, or you pay the $$$ to put it on a scanner.

------------------
Ed Maher - Moderator @ The Carb Board
92 Z28 Convertible - Quasar blue / Tan top
LB9 4L60 GU2 G80 - stock, soon to be sleeper
-=ICON Motorsports=-

- Definitely prototypes, high powered mutants of some kind. Too weird to live, too cool to die

 

the engine is the old LB9. the distributor looks good. i have inspected it and it isn't broken or cracked anywhere and all the components in the distributor have been replaced without effecting the repair (problem existing before and after replacing parts). i still have a problem when i hook up the wire. it's holding it's base timing at 8* with the wire unplugged so i don't think it's distributor related... i have tried inspecting it and it looks good, filiments are not broke, plugged the wire in and tapped on it with the engine running and it didn't stumble. so other than hooking this up to a scanner there are no testing procedures that can be followed?

 

ok, hooked into diagnostic mode again and this time i have stored codes, 42 and 43

 

You still didn't say if it is MAF or MAP.

As for testing sensors, i just went through what they are, but i can't tel you exactly what values they should all show. Checking the TPS is easy enough and is outlined around here a million times. If it's a MAP car, you should see a high voltage at the MAP output with the car off (pressure high) and a lower voltage with the engine idling (don't know what V = what pressure offhand though.) If it's a MAF car, well, if you had the ability to check it, you would know it, you'd need an osciloscope for starters.
The other sensors, like the CTS, and BARO (which i think MAF cars use) wouldn't hurt you this bad if they were bad. It would have to be one of the major sensors.

But basically i was just trying to say that just cuz you had the dist. apart before, doens't mean you shouldn't follow GMtech's advice now. You are in an ugly situation, if i had somebody trying to hold my hand, i'd take it, not second guess the diagnosis.
Admittedly, this would prolly be a lot easier with a scanner.

 

Here's an idea from a non-gm-certified-tech... how's your balancer? If the rubber ring has deteriorated, the outer ring could've spun on the balancer. This would throw your timing mark off! Bring the #1 cyl up to TDC, and make sure the mark in the balancer aligns with the 0 degree advance mark on your timing indicator. If the ring shifted enough, your base timing could be way off what you think it is. What you're doing for 8 deg advance could wind up being 18 deg advance!

That code 42 is probably from the unhooking of the EST bypass connector... the computer didn't know you unhooked it on purpose. Code 43... don't know.


------------------
-Tom P (Hot rodded 1986 Firebird 2.8l) from http://www.f-body.net/mailbag/3rd/3rd_mailbag.html message boards
---Think your car could be pic of the week? Visit http://www.f-body.net for details!

 

Well, I am a GM tech, or used to be anyways, but I still don't know as much as a lot of the guys on here.

OK, ENOUGH with the politics - EVERYBODY.

Since you said it is an 'old' LB9 I assume it is MAF. Your problems sound exactly like the symptoms of a toasted MAF sensor. But if you do not have a scanner, you will not be able to diagnose this yourself properly. I also do not recommend putting the old double barrel on full-choke and firing more parts at the car either. Try asking around and see if any of your friends/acquaintences have a 'test' MAF sensor. That way you can try a known good one on the car. I really can't help ya much on this since I cannot actually see or examine the car, but I have seen symptoms like the ones you describe a lot with bad MAF sensors.

Hope that helps some.

my $.02

Laterzzzzzzzzzzzzzzzzzzzzzzzzzz

------------------
Matt

1987 GTA L98 MD8 GW6

"Stop Lights timed for 35Mph are also timed for 70Mph"

 

it's a maf system. i'll look around for a maf sensor to try. would the maf be sending any thing to the computer at idle, wouldn't i get a code?

 

I found something in my GM book while looking for something else....

Maybe that'll help.


------------------
-Tom P (Hot rodded 1986 Firebird 2.8l) from http://www.f-body.net/mailbag/3rd/3rd_mailbag.html message boards
---Think your car could be pic of the week? Visit http://www.f-body.net for details!

 

Quote:

<font face="Verdana, Arial" size="2">would the maf be sending any thing to the computer at idle, wouldn't i get a code?

The MAF is ALWAYS sending data to the ECM. The question is when the ECM pays attention to the MAF, like it ignores MAF signals at WOT. Now next question: Is it an '85 or '86-'89 setup? The '85 is a totally different animal, and troubleshooting is somewhat different than it is for the '86-'89 MAF cars.

------------------
Kevin Irving
85 Trans Am WS-6, 305 TPI, custom burned '86 PROM with '87 "165"ECM, Accel Supercoil & 8.8 Wires, Rapidfire #2 @ .055", MSD 6AL, 1.6:1 Roller tipped rockers, Homemade AFPR, K&N cone, no airbox, Aluminum Driveshaft, Wonderbar, TB Coolant Bypass, Ported Plenum, Descreened MAF, Syclone Fuel Pump, JET Airfoil, Mobil 1 synth in all but transmission.

15.556 @ 86.65mph, Nov 10, 2000.... I know it sucks.. but it will get better!

http://www.geocities.com/transam85tpi/

Member - The Tidewater Trans Am Club, Norfolk VA http://www.geocities.com/ttacva/

[This message has been edited by Kevin Irving (edited May 09, 2001).]

 

ok, went back and inspected the distributor components and everything looks good. checked the harmonic balancer and it looks almost new and is timed with piston #1. coil tests good. replaced the o2 sensor and knock sensor, they looked like crap! it seems to have helped a little but now acts a little sluggish at times and still backfires but not half as much. oh, its the 85 maf system.

 

I thought I told you NOT to fire more parts at the car????

------------------
Matt

1987 GTA L98 MD8 GW6

"Stop Lights timed for 35Mph are also timed for 70Mph"

 

Well, that certainly made sense. You replaced one sensor that couldn't possibly have been affecting your problem, and the other one could have been ruled out w/ a $0.05 resistor. So now you have prolly spent at least $60-80 on more parts that any of us could have told you wouldn't help, and meanwhile you probably need a $450 MAF (just guessing price, but i know it is gonna kick you in the nuts when you see the price.)
lol, are you trying to fix this car, or are you just independently wealthy and bored?
...ed

 

Dude that is funny a$$ed $hite...........

------------------
Matt

1987 GTA L98 MD8 GW6

"Stop Lights timed for 35Mph are also timed for 70Mph"

 

Dude that is funny a$$ed $hite...........

------------------
Matt

1987 GTA L98 MD8 GW6

"Stop Lights timed for 35Mph are also timed for 70Mph"

 

ha ha ha ha, you guys are harsh! had to replace the sensors anyway while i was cruising around the engine i noticed the o2 was broke and the knock was rusted out bad... i'm going to get it scanned and find out if i really need a maf or if it's something else.