Pennock's Fiero Forum
  Technical Discussion & Questions
  No movement on the tach when cranking

Post New Topic  Post A Reply
Email This Page to Someone! | Printable Version


next newest topic | next oldest topic
No movement on the tach when cranking by Additivewalnut
Started on: 02-13-2020 12:19 PM
Replies: 12 (154 views)
Last post by: fierofool on 02-14-2020 08:07 PM
Additivewalnut
Member
Posts: 14
From: Saint Louis, Missouri
Registered: Jan 2020


Feedback score: N/A
Leave feedback

Rate this member

Report this Post02-13-2020 12:19 PM Click Here to See the Profile for AdditivewalnutSend a Private Message to AdditivewalnutEdit/Delete MessageReply w/QuoteDirect Link to This Post
Alright, pay check came in, I'm ready to buy more parts for my problem child. I've narrowed it down to the pickup coil since I replaced the ICM and nothing happened. So. Do I need to replace anything along WITH the pickup coil as to not make it burn out the moment I turn the key? Or is it just pickup coil and done?

Oh there's an o ring I have to install too isn't there?
IP: Logged
PFF
System Bot
fierofool
Member
Posts: 11600
From: Auburn, Georgia USA
Registered: Jan 2002


Feedback score:    (13)
Leave feedback





Total ratings: 150
Rate this member

Report this Post02-13-2020 05:03 PM Click Here to See the Profile for fierofoolClick Here to visit fierofool's HomePageClick Here to Email fierofoolSend a Private Message to fierofoolEdit/Delete MessageReply w/QuoteDirect Link to This Post
Pickup Coil, Ignition Module and Ignition Coil supply the spark. If the other components are good, as you indicate, replace the distributor O-ring when you reinstall the distributor. I don't know if it's available as listed for the Fiero, but it may be for the 93-95 Camaro and Firebird 3.4 oil pump drive. It's FelPro Part # 70800.
IP: Logged
Additivewalnut
Member
Posts: 14
From: Saint Louis, Missouri
Registered: Jan 2020


Feedback score: N/A
Leave feedback

Rate this member

Report this Post02-13-2020 05:36 PM Click Here to See the Profile for AdditivewalnutSend a Private Message to AdditivewalnutEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by fierofool:

Pickup Coil, Ignition Module and Ignition Coil supply the spark.


Oh wait hold up then, would a bad ignition coil cause the tach to not move when cranking? From my research, only the ICM and the pickup would cause it not to..
IP: Logged
Dennis LaGrua
Member
Posts: 13078
From: Hillsborough, NJ U.S.A.
Registered: May 2000


Feedback score:    (11)
Leave feedback





Total ratings: 316
Rate this member

Report this Post02-13-2020 06:50 PM Click Here to See the Profile for Dennis LaGruaClick Here to Email Dennis LaGruaSend a Private Message to Dennis LaGruaEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by Additivewalnut:


Oh wait hold up then, would a bad ignition coil cause the tach to not move when cranking? From my research, only the ICM and the pickup would cause it not to..


The tach pulses are taken from the igniton module to the coil. Iif the coil was defective and all else is good then the tach will show movement. The only other thing that could cause a tach not to get a signal is a bad tach filter.

------------------
" THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite.
"THE COLUSSUS"
87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H
" ON THE LOOSE WITHOUT THE JUICE "

IP: Logged
Additivewalnut
Member
Posts: 14
From: Saint Louis, Missouri
Registered: Jan 2020


Feedback score: N/A
Leave feedback

Rate this member

Report this Post02-13-2020 06:56 PM Click Here to See the Profile for AdditivewalnutSend a Private Message to AdditivewalnutEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by Dennis LaGrua:


The tach pulses are taken from the igniton module to the coil. Iif the coil was defective and all else is good then the tach will show movement. The only other thing that could cause a tach not to get a signal is a bad tach filter.



The tach was moving fine when the car died, now it doesn't move when cranking..
IP: Logged
Gall757
Member
Posts: 10384
From: Holland, MI
Registered: Jun 2010


Feedback score: N/A
Leave feedback





Total ratings: 87
Rate this member

Report this Post02-13-2020 08:50 PM Click Here to See the Profile for Gall757Send a Private Message to Gall757Edit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by Additivewalnut:


The tach was moving fine when the car died, now it doesn't move when cranking..


By an wide margin, the most likely problem is the ICM. They die in all sorts of ways, sometimes right out of the box.

[This message has been edited by Gall757 (edited 02-13-2020).]

IP: Logged
Additivewalnut
Member
Posts: 14
From: Saint Louis, Missouri
Registered: Jan 2020


Feedback score: N/A
Leave feedback

Rate this member

Report this Post02-13-2020 09:43 PM Click Here to See the Profile for AdditivewalnutSend a Private Message to AdditivewalnutEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by Gall757:


By an wide margin, the most likely problem is the ICM. They die in all sorts of ways, sometimes right out of the box.



Hmmm.. how do I test if mine's bad? I dont really want to just keep buying them if that's not the problem
IP: Logged
DavidM
Member
Posts: 73
From: Arlington TX USA
Registered: Oct 2009


Feedback score: N/A
Leave feedback

Rate this member

Report this Post02-13-2020 11:39 PM Click Here to See the Profile for DavidMClick Here to visit DavidM's HomePageClick Here to Email DavidMSend a Private Message to DavidMEdit/Delete MessageReply w/QuoteDirect Link to This Post
First, make sure the distributor is actually turning. You can test the pickup coil's resistance with a meter - should not be open. Make sure that the power & ground is making it to the ICM (and check the pickup connection to the ICM.

Check the connections to the coil. I have not tried a test light on the signal to the coil (I used oscilloscopes) but I don''t see why that would not work if the ground lead of the test light is on the +ve. Possible that the tach filter is shorting out the signal but unlikely.

Could be just another bad new ICM of course. They used to be able to test them at the parts stores - don't know if they still can.

Keep at it! You'll solve it. Measuring is cheaper than the parts cannon!
IP: Logged
Additivewalnut
Member
Posts: 14
From: Saint Louis, Missouri
Registered: Jan 2020


Feedback score: N/A
Leave feedback

Rate this member

Report this Post02-14-2020 03:11 AM Click Here to See the Profile for AdditivewalnutSend a Private Message to AdditivewalnutEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by DavidM:

Could be just another bad new ICM of course. They used to be able to test them at the parts stores - don't know if they still can.


I actually got my old ICM tested and they said it passed all the tests they put it through... I still bought a new one though just in case. I also bought a new ignition coil and have only run the car for a total of 1.5 hours. Everything seems to be pointing at the pickup coil going bad after sitting for so long. But I'll check everything, I need to go buy thinner multimeter leads to actually fit in the connector LOL
IP: Logged
fierofool
Member
Posts: 11600
From: Auburn, Georgia USA
Registered: Jan 2002


Feedback score:    (13)
Leave feedback





Total ratings: 150
Rate this member

Report this Post02-14-2020 08:35 AM Click Here to See the Profile for fierofoolClick Here to visit fierofool's HomePageClick Here to Email fierofoolSend a Private Message to fierofoolEdit/Delete MessageReply w/QuoteDirect Link to This Post
In the old harnesses, the clipss on the ends of the wires can get pushed back into the harness ends. It may not have caused the initial problem but look into the end of the plug and see if all the clips are at the front, equally. The pins on the ICM or other sensors can sometimes push the clips back inside, allowing the sensor to work for a while before it loses contact.

Have you checked a plug wire to see if you have fire on it? And since you have removed the distributor to replace the pickup coil, did you check the distributor cap to be sure the carbon button didn't fall out, or did you make my mistake and fail to reinstall the rotor button ?
IP: Logged
Additivewalnut
Member
Posts: 14
From: Saint Louis, Missouri
Registered: Jan 2020


Feedback score: N/A
Leave feedback

Rate this member

Report this Post02-14-2020 12:20 PM Click Here to See the Profile for AdditivewalnutSend a Private Message to AdditivewalnutEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by fierofool:

In the old harnesses, the clipss on the ends of the wires can get pushed back into the harness ends. It may not have caused the initial problem but look into the end of the plug and see if all the clips are at the front, equally. The pins on the ICM or other sensors can sometimes push the clips back inside, allowing the sensor to work for a while before it loses contact.

Have you checked a plug wire to see if you have fire on it? And since you have removed the distributor to replace the pickup coil, did you check the distributor cap to be sure the carbon button didn't fall out, or did you make my mistake and fail to reinstall the rotor button ?



I actually haven't removed the distributor yet... are you saying it could just be the wiring harnesses from the ignition coil to the ICM? Also this makes me wonder... what is the carbon botton and also what is the rotor button...? I have never heard of those pieces before! GAH THIS IS SCARY.
IP: Logged
PFF
System Bot
Will
Member
Posts: 13089
From: Where you least expect me
Registered: Jun 2000


Feedback score: (1)
Leave feedback





Total ratings: 235
Rate this member

Report this Post02-14-2020 03:29 PM Click Here to See the Profile for WillClick Here to Email WillSend a Private Message to WillEdit/Delete MessageReply w/QuoteDirect Link to This Post
If you haven't removed the distributor since the last time the engine started, that's good... you don't have to check to make sure the dizzy is correctly timed.
IP: Logged
fierofool
Member
Posts: 11600
From: Auburn, Georgia USA
Registered: Jan 2002


Feedback score:    (13)
Leave feedback





Total ratings: 150
Rate this member

Report this Post02-14-2020 08:07 PM Click Here to See the Profile for fierofoolClick Here to visit fierofool's HomePageClick Here to Email fierofoolSend a Private Message to fierofoolEdit/Delete MessageReply w/QuoteDirect Link to This Post
The rotor button is that round plastic piece with the metal pointer and it sits on top of the distributor shaft, inside the distributor cap. The carbon button is in the centeer of the distributor cap. It's spring loaded so that it keeps pressure against the very center of the rotor button. It transfers the spark from the ignition coil wire to the spark plug wire terminals inside the cap.

One of our club members had worked for months or maybe more than a year trying to get a Fiero to run. I checked the harness and one of the wires had pushed back into the harness end. It's not that uncommon. I saw an 88Gt that a Nissan dealer couldn't get running. They pulled the man's car out into a dirt lot down back and left it. It sat so long the brakes locked down. He became so disgusted that he put the car up for sale for a few hundred dollars. One of our members bought it, checked the pins in the harness. Problem solved and the car started on the spot.

For some reason, every one I've seen has been the fuel pump signal wire. You can test for fuel pressure by spraying a little starting fluid or even brake cleaner into the throttle body to see if it will momentarily start.
IP: Logged

next newest topic | next oldest topic

All times are ET (US)

Post New Topic  Post A Reply
Hop to:

Contact Us | Back To Main Page

Advertizing on PFF | Fiero Parts Vendors
PFF Merchandise | Fiero Gallery | Ogre's Cave
Real-Time Chat | Fiero Related Auctions on eBay



Copyright (c) 1999, C. Pennock