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mikekath@iafrica.com
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UNABLE TO START ENGINE - GTV6 BOSCH L-JETRONIC GURU’s PLEASE HELP!

Post by mikekath@iafrica.com »

Sorry for the long post, but I think the info is needed by you to understand what has been done and checked.
I have asked some questions at the end that I would like to close out.

Some background:
Have been rebuilding a 1982 GTV6 for 4 years in South Africa. Car finally all back together but cannot get it started. Engine was rebuilt by Dawie De Villers and he has also been assisting as has Kevin Rascher with troubleshooting this matter.
Car was running prior to this but engine needed overhaul badly (as did the whole car πŸ˜‰)
Checks done:

FUEL TO ENGINE
There is a new fuel pump fitted.
Fuel pump operates on ignition crank (purple wire from ignition switch to combi relay)
Fuel pump functions fine using the air flap on the AFM when ignition is on
The operation of this via the combi relay is nicely described in this post
https://www.alfabb.com/threads/bosch-do ... st-8803990
The fuel pressure is fine.
I had to install my 10th relay to the car to get the current adequate for the crank cycle. (4 relays for headlights, 2x2 for electric windows, 1 for ignition switch to fuse box (brown wire) and now 1 for ignition switch crank to shared starter wire (black) and fuel pump (purple).

SPARK
New coil installed.
Spark tested to distributor on main HT lead.
Spark tested to spark plugs.

BOSCH L-JETRONIC
The issue is somewhere in this system. THERE IS FUEL TO INJECTORS, THERE IS SPARK, BUT THE PULSE TO THE INJECTORS IS NOT WORKING, HENCE NO FUEL INTO CYLINDERS ON CRANK.
The L-Jetronic harness has been β€œoverhauled” with new terminals and plugs to all injectors and sensors and new glass fibre harness sleeves. These were all replicated to the original setup (wire colours and positions). The terminals on the 2 combi relay connection blocks were not touched.
The following has been tested on this L-Jetronic system
ECU connector wiring continuity – CHECKED
All these wires were tested for continuity from the ECU plug through to where they terminate as described below.
T1 – White to firewall terminal block (round pin with nut), matched with coil -ve
T2 – White to throttle switch
T3 – Yellow to throttle switch (T3)
T4 – Gray/green to Bosch harness connection block (Combi relay) T86
T5 - Black to earth wires on valve cover
T6 – Green to AFM (T6)
T7 – Black/white to AFM (T7)
T8 - Brown/white to AFM (T8)
T9 – Blue/white to AFM (T9)
T10 – Red/black to Bosch harness connection block (Combi relay) T88a
T11 – Not used
T12 – Not used
T13 – Brown to CTS (Coolant temperature sensor)
T14 – Blue/red to Injector #4 (-ve)
T15 – Green/white to Injector #1 (-ve)
T16 – Black to earth wires on valve cover
T17 – Black to earth wires on valve cover
T18 – Purple to throttle switch (T18)
T19 – Not used
T20 – Pink/black to Bosch harness connection block (Combi relay) T86b
T21 – Not used
T22 – Not used
T23 – Not used (no lambda sensor fitted)
T24 – Not used (no lambda sensor fitted)
T25 – Not used
T26 – Not used
T27 – Grey/red to AFM (T27)
T28 – Yellow/red to Bosch harness connection block (Combi relay) T85
T29 – Red (thick) to Bosch harness connection block (Combi relay) T88b
T30 – White/red to injector #5 (-ve)
T31 – Blue/yellow to injector #6 (-ve)
T32 – Black/yellow to injector #3 (-ve)
T33 – Orange/white to injector #2 (-ve)
T34 – Orange to (AAV) auxiliary air valve
T35 – Black to earth wires on valve cover

Combi relay – CHECKED
This was done as per a useful post from an Alfa Australia site:
Simple Testing Procedure for GTV6 Dual Relay
Test 1 - Check the relay coils
1. Connect your earth to pin 85 of the relay
2. Connect 12v to pin 86C
You should hear a click - cool one works :)
Now
1. Leave your earth on pin 85
2. Connect 12v to pin 86B
You should hear another click :)
Now connect 12v to pin 86 and you should hear another click.

Test 2 - Check the contacts.
1. Connect earth to pin 85 and 12v to pin 86, you should get a click so leave it connected.
2. Set multimeter to one of the OHMS ranges to check resistance and connect one lead on pin 88C and the other lead on pin 88D you should read 0 Ohms or a short here - those contacts are good :)
1. Now leave the earth where it was and connect 12v to pin 86C, you should get another click so leave it connected.
2. Multimeter on OHMS again one lead on 88Z and the other on 88B and you should get another short - all good.

CTS (Coolant temperature sensor) – CHECKED
New CTS was fitted
Wire (brown) traced back to ECU T13
Earth (black) traced back to earth wires on valve cover
Resistance checked with cold engine at 2400ohms (in spec)

AFM (Air Flow Meter) wiring – CHECKED
5 ECU wires traced back to ECU terminals (T27-Gray/red), T7-white/black, T8-brown/white, T9-blue/white, T6-green)
2 combo block harness wires traced back (pink/black=86b, red/black=88a)

Throttle switch, AAV, cold start injector, thermos time switch – continuity test
Tested all wiring from these sensors back to source and all were complete circuits

Injector power plug test - CONCERNED
ECU connected
With ignition off and multimeter earthed, neither terminal on the injector leads has any voltage, this seems correct
With ignition on and multimeter earthed, BOTH terminal on the injector leads are showing 12v. I understand that the +ve lead should show that, but the -ve pulse wire should surely not?

Combi relay to relay terminal blocks matching
Although I did not remove the copper terminals from the 2 white combi relay connection blocks, I wanted to check that they made sense.
I found this a mind game as you have to mirror the relay terminals to the connection blocks (hope that makes sense? πŸ˜‰).
The white blocks are number 1-9 and the relay uses different numer/alpha names.
This is what I have and would like it confirmed if someone has the info:

Bosch terminal block (this is Bosch harness side – more wires/terminals used )
Block T1 = Relay 86b pink/black (2) to ECU20 and AFM T36
Block T2 = Relay 88c orange/black (1) to AAV
Block T3 = Relay 85 orange/red (1) to ECU 28 (is this the relay ground?)
Block T4 = Relay 88a red/black (2) to ECU10 and AFM T39
Block T5 = Relay 88e red (2) to Injectors 3&4 +ve
Block T6 = Relay 88f red (2) to injectors 1&2 +ve
Block T7 = Relay 86 green/grey (2) to ECU4 and Cold start injector
Block T8 = Relay 88b red (3) to Injectors 5&6 +ve and ECU T29
Block T9 = Not used

Main terminal block (this is block from main harness side – fewer wires/terminal used)
Block T1 = Relay 86a purple (1) from ignition switch
Block T2 = Relay 88y red (1) from fuse box fuse 5 – always
Block T3 = Not used
Block T4 = Not used
Block T5 = Not used
Block T6 = Relay 88z red (1) from firewall power junction block
Block T7 = Not used
Block T8 = Relay 88b pink/white (1) to fuel pump
Block T9 = Not used

Earth wires
I know these are critical and have double-checked
Plenum to block (thin braided wire)
Block to engine bay near coil (thick wire)
Block to undercarriage (thick braided wire)
All Bosch harness ground wires to valve cover bolt.
All earth wires to the RHS dashboard bolt

QUESTIONS FOR FORUM MEMBERS
  • There was a small resistance on the contacts checked on the combi relay (less that 1 ohm), could this be an issue?
  • Is the yellow/red from T28 of the ECU to the Combi block T85 the GROUND for the combi relay? From what I can establish, if the ECU is not connected, the grounding needed on T85 of combi relay is missing and relay will not trigger?
  • Where does the trigger signal come from to tell the ECU to pulse? I understand that to be from the -ve terminal on the coil (white wire to ECU T1), is that correct? How do you test that is working?
  • Why are the NEGATIVE pulse wires on the injectors carrying a 12v current when the ignition is switched on? Surely this should show 0v based on ground to ground circuit? What would cause this to happen, a faulty combi relay or ECU?
  • On the terminal block (round with nut) that links 2 white wires (coil -ve and throttle switch) to the wire that goes to ECU T1, the wire to the ECU has a core and shield. The core goes to ECU T1, and the shield wire (earth) is pig tailed at the terminal block and joins into an earth wire of the other main engine harness. Where does the other end of the shield terminate? Could this be part of the problem?
  • Without a noid light to test pulsing to the injector terminal, is it safe to use a normal light tester across the 2 terminals?
  • The Bosch side combi relay block gets 12v on terminal 88z directly from the smaller battery wire terminal block on the firewall. Getting 12v with no fuse in line, is that not risky?
  • Can you confirm the combi relay & block referencing I have noted. Does it match yours?
  • What else can I check?
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