How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site.
    Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask Tims Auto Repair Your Own Question
Tims Auto Repair
Tims Auto Repair, GMC Mechanic
Category: GMC
Satisfied Customers: 15487
Experience:  have owned a repair shop for 25 years
14541291
Type Your GMC Question Here...
Tims Auto Repair is online now
A new question is answered every 9 seconds

We have an 86 s-10 blazer with the 2.8L engine and the TBI.

Customer Question

ny suggestions
Submitted: 1 year ago.
Category: GMC
Customer: replied 1 year ago.
We have an 86 s-10 blazer with the 2.8L engine and the TBI. Historically it has had issues seemingly running too rich on start as I would need to race the engine under no load on start to clear excessive fuel. Then as ambient temperature raises above 80 degrees the engine will behave as if it vapor locks until it cools back down and then it will start again.Recently my son has been driving it as his daily driver and it has been throwing codes of lean O2 sensor and sometime when cruising about 50 mph it will present a check engine then clear itself.This last week it just flat stopped running. It would start however if the throttle is pressed at all the engine will choke and stall.We purchased new injectors and a TBI rebuild kit (and installed them), replaced the O2 sensor, replaced driver side exhaust manifold (found this can present lean O2 reading). Now the injectors do not pulse any fuel. Pulling the top off the injector housing and it is charged with fuel. Loosening the fuel line shows pressure on the lines.Replaced the Cap & rotor & wires and had the Ignition module (under rotor) tested at local parts house and it tested good 3xWe tested the connector and red & white leads show +12v and lt blue & lt green have 0 ohm resistance to D14&D16 of the ECM.I checked the TPS and at "idle" it shows .3v and WOT reads 3.45vIf we dribble gas into the plenum it will start and run.I just tried "rebooting" the ECM by removing the battery cable for five minutes and re connecting it to no avail.We have exhausted our possibilities and are needing some advice.
Expert:  Pete replied 1 year ago.
My name is ***** ***** I am a professional here at Just Answer. I noticed that your question was not getting a response and thought I would see if you still need help with this.I apologize for the delay and I hope I can still assist you with this here.
One common component that fails and prevent injector pulses is the pick up coil under the rotor in the distributor itself,this is a separate coil from the external coil outside of the distributor.This coil should read between 500 and 1500 ohms of resistance when tested at the two wires that lead from it to the ignition module.If you have more or less resistance then it needs replaced.It can be replaced separate of the distributor but in some cases replacing the distributor assembly is easier.If this was not tested this needs done as I suspect this is the cause here.If it was tested or replaced already let me know so we can continue.
Thanks Pete
Customer: replied 1 year ago.
We have tested so much on this that I lost track of everything we have done.
We have used a timing light and tested each spark plug wire and there is spark to each cyl thus the running on dribbled gas. Wouldn't this indicate the pickup coil is receiving signal? I just tested the coil and it shows 759 ohm at the ICM , the 4+2 pin module under the rotor. I took the ICM into the parts house and they tested it 3x successful cycles even after warming it up. I tested the connection from the ICM to the coil and it is good. The injectors still do not fire. I checked for "Pulsing" ground at the injector plug to verify that it's not a faulty injector and confirmed that it is not there.. but +12V is present to the other side of the injector plug.
Expert:  Pete replied 1 year ago.
Is there any corrosion under the rotor in the distributor at all?Green or red corrosion of any kind?
Let me know,thanks Pete.
Customer: replied 1 year ago.
We don't see any issue with corrosion however here are some pictures.
If there was corrosion or issues with the pickup coil wouldn't it interfere with the engine running while manually dribbling in fuel?The engine ran (albeit VERY POORLY) before pulling it into the garage. it would die if placed under any load. However it would crank and start then we replaced the parts and now it doesn't spray fuel. What would cause the injectors to suddenly not fire?If it is an issue with the ICM signal wire (pin B) is that what tells the ECM to fire the injectors?Dave
Expert:  Pete replied 1 year ago.
O.k.,I see no corrosion so this should be o.k.
Is your throttle position sensor plugged in properly with no bent terminals or pins in it and is it damaged at all?
If it is o.k. if you unplug it does it fire up then at all?
Customer: replied 1 year ago.
TPS is fine. I tested it earlier and it has steady power response through entire range of motion. Unplugged and no fuel fires. engine doesn't start
Expert:  Pete replied 1 year ago.
Since this occurred after work had been done did you double check and make sure no wiring was damaged or bumped loose?
Customer: replied 1 year ago.
I've gone through the only wiring that we touched and no pins were bent nor pulled loose of their connectors.
When removing the TBI we disconnected the TPS and the MAP Sensor and the 4pin quad sensor next to the TPS (i still can't figure out what that does) but the connections are good.
Then I also took off the ICM under the rotor and made sure that it was plugged back in successfully.
Expert:  Pete replied 1 year ago.
The quad sensor may be the idle air control motor but this won't cause the issue here.
Since the ignition module has been tested repeatedly and found ok I don't think this is the cause.The only other component that the fuel injector signal comes from is the ECM itself and I have seen it fail before and cause this here and had to replace it.
Thanks Pete
Customer: replied 1 year ago.
We went a bought a $100 ECM and installed it but the same issue persists. No fuel is emitted from the injectors. What pin does the ICM talk to the ECM to see if there is signal getting to the ECM?
Expert:  Pete replied 1 year ago.
Did you remove the prom chip from the old ecm and plug it into the new ecm?
Customer: replied 1 year ago.
Yes we moved the prom from old to new before testing.
Expert:  Pete replied 1 year ago.
Does your model have the electronic spark timing control module at all?
Customer: replied 1 year ago.
Isn't that the ICM that is under the pickup coil in the picture above?
Expert:  Pete replied 1 year ago.
No this would be a separate control module,a little black box usually on the intake.
Customer: replied 1 year ago.
There is a MAP sensor on the intake and another module on the firewall behind the Distributor.
MAP Sensor tested good.
Expert:  Pete replied 1 year ago.
What color wires are in the connector at this black box on the firewall?
Customer: replied 1 year ago.
the color of wires that plug into that box are blue, black, what appears to be gray and brown.
Expert:  Pete replied 1 year ago.
O.k.,under the dash above the brake pedal on a bracket is there another square type box with an electrical connector plugged into it with a pink,dark blue,brown,light green,white,and black wire in the connector?
Customer: replied 1 year ago.
The odbc connection to check the trouble codes? Or a different box?
Customer: replied 1 year ago.
Here's a link to hi-res images of the underside of the dash. What black box are you talking about?
https://www.dropbox.com/sh/wxn0m72nngzpns9/AAC8xuFiQT7ZBqWh1BRRwKcha?dl=0
Expert:  Pete replied 1 year ago.
Below are the links for the esc control module and controller.Let me know if you see these under the hood on one of them and under the dash.
https://www.dropbox.com/s/4s81bcewc4el5b0/esc-06-05.gif?dl=0
https://www.dropbox.com/s/jzphplqbzyqx2oq/esc1-06-05.gif?dl=0
Thanks Pete
Customer: replied 1 year ago.
Yes it does have a Spark Control Module That was the box that I sent the picture of on the firewall but the wire colors are different than what you had suggested. It is a 5 pin module with four wires attached. Pink/blk, brown, black, dk blue.
ECM A6 pink/blk
DK Blue--> Knock Sensor
Brown goes to a junction to connect to Blk/white
BLK ECM B7
Customer: replied 1 year ago.
Also with new ECM installed no Fuel was present so we replaced fuel pump and now have 14lb static fuel pressure.
Customer: replied 1 year ago.
Found a diagram of the Spark Control module and it looks like I can simulate normal conditions if I bridge pink & black. But the description indicates that it has nothing to do with injector firing or not just would retard timing if knock is sensed while engine running.
This is the same module that i have... http://members.shaw.ca/corvette86/Electronic%20Spark%20Control.pdf
Expert:  Pete replied 1 year ago.
This is a difficult one for me to be able to fully answer from here.I will have to open this question up for others here to see if they can assist further on this as someone else here may have more info on what to check or do with this issue.I hope you can get this resolved with ease.No need to reply to my last post here unless it is a last resort as it will keep your question locked to me and others will not be able to view it.
Thanks Pete
Expert:  Tims Auto Repair replied 1 year ago.
Hi,My name is Tim,
I will do my best to assist you
sense you get no pulse..first,double check the wiring and the wiring harness..
i would think your problem is in fact the ignition module or the pick-up..i know you have tested,,but the ignition module test only tests the spark...
you may just want to replace the complete distributor with a new rebuilt unit.
if the distributor doesnt fix your problem[i think it will] then the problem is the ecu[computer itself]
thanks
If you are satisfied with my answer, Please Rate my answer by clicking the rating button so I can get credit for my work. I’m not always going to be giving you good news, so please don't let this stand in the way of you accepting my answer. .it does not cost you more money and we will still be able to communicate, ,.please understand, i can not see, hear or touch the vehicle and only know what you tell me. Bonuses and positive feedback are appreciated.. if you are not satisfied with my answer, please do not leave bad feed back ,i will gladly opt out and let another expert handle the question. .if i have sent any diagrams, please print them. .sometimes you may need to right click the image [,then save picture as]to save it to your computer so you can open it with your picture program...Please ask if you need more help.
Customer: replied 1 year ago.
Tim, I just replaced the ICM and plugged it back in. I also tested the lead from the ICM to D6 on the ECM and it is good If that system is functioning what Voltage should I be seeing on D6 when spark should be firing?
Expert:  Tims Auto Repair replied 1 year ago.
: OE does not supply any Component testing for the Ignition Control Module. The way OE has you Test an Ignition Module is by checking for proper inputs. If all the inputs are there, and the module doesn't either fire a coil, and/or referance the Engine Control Module (to energize an injector), the Ignition Module is bad.
If the vehicle cranks for at least 5 seconds and the Engine Control Module doesn't see a referance signal, some Models will set a code, 42 (Hard) or 12 (Soft). If your vehicle has one of these codes, begin with the Diagnostic System Check in Computers and Controls, then proceed to the Trouble Code Chart (Yes, some vehicles have a DTC Chart for Code 12).
If the vehicle does not set a code, begin with the Diagnostic System Check, and it will send you to a Diagnostic Chart that checks for your particular condition.
Customer: replied 1 year ago.
Tim,
Our local parts house has a computer that will test the Ignition Control Module as referenced above. However I went ahead and purchased another one just in case those tests were incorrect and it did not resolve the fuel issue. In Field Service Mode the computer flashes code 12 and no others. My book doesn't show a diagnostic test for a code 12. I don't have a flow chart for a diagnostic system check that you are referring to. In reading other forums I've seen that other sensors will cause the ecm to not send "fire" signal to the injectors as it thinks it's clearing a flood situation etc. What should I be looking for that would be sending these codes to the ECM?
Expert:  Tims Auto Repair replied 1 year ago.
code 12 means the the dignostic system is working..
code 12 is not a trouble code..
if you have checked the wire harness and all is well..you have a bad pick-up coil in the distributer or a bad ecm[computer] itself
thanks
Customer: replied 1 year ago.
After finding the Chevy Drivability shop manual it showed testing the Pink/white wire B5 of the ECM to +12v and see if the injector fired. This worked so tracing that wire back to the distributor the ICM only had one plug attached to the 4 pin side (pickup coil) the ESC connector wasn't attached thus no signal to the ECM for fuel. Attached that wire and all was fine.
Customer: replied 1 year ago.
I hope this can get back to Pete. He was right it was the ignition module but it was just a connector that was missing. I tried attaching the drivability log to the post but it's too big. I will put in the dropbox folder I sent to Pete and hope he can get it.
Expert:  Tims Auto Repair replied 1 year ago.
glad you got it going
thanks for using justanswer

Related GMC Questions