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1990 740 GLE 16V. Check engine light, rough start and low rough idle. Intermittent crank-no start.

ZVOLV

ZVOLV

<Master Tech>
Joined
Nov 19, 2002
Location
West Texas
I just bought this car and giving it the shakedown.


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-CEL diagnosed as LH box throwing false 2-1-3 (Throttle position sensor) code. Confirmed TPS circuits were OK. Replaced LH box and it fixed the false TPS code.

6/30/25- Intermittent stalling/crank-no-start still present. Got a 1-3-1 (ignition signal during cranking code). Replaced the crankshaft position sensor with a new Bougicord sensor. No stalling/crank-no-start, and no codes so far.

7/2/2025- Been daily driving it and LH has relearned idle speed and the car has been running just fine and no more check engine lamp.

7/10/205- One time did a crank-no-start.

8/17/2025- Stalling at idle and running poorly. 3-1-2 (EZK load signal), 2-2-1 (fuel trim off-idle), and 2-3-2 (fuel trim at-idle) codes stored. I also had a 1-2-1 (MAF code).

8/20/2025- The engine has done the crank no-start/stall only two times in two months. A couple instances of stalling/poor idle 3-1-2 (EZK load signal) was stored, but no check engine lamp. Engine bay has degraded insulation at the connectors.

8/24/2025- Repaired failing wiring for the engine-to-body wiring harness with OEM repair leads.

9/3/2025- Has been running great, but today I lost power while accelerating. Power went "flat". Engine stalled at idle speed. Crank-no-start a few times and then fired back up and drove fine.

10/1/2025- Did the crank-no start again. It eventually fired up and drove fine. Diagnosis continues... LH box stores a 3-1-2 (EZK load signal) after the intermittent crank-no-start. No Check Engine Lamp (CEL)

12/15/2025- Been running fine. Fixing corroded wiring at the fuel pump, oily spark plug wells, leaking distributor, worn cap/rotor.


$3 test lamp, $20 terminal test probes, $5 noid light, and free wiring diagrams (thanks again). These tools have currently lead me to the diagnosis of the issues as:

1. PCV hose air leaks
2. torn FPR hose
3. degraded RSR wiring
4. LH box throwing fake TPS code and intermittently not operating the LH/fuel pump relay. LH box replaced.
5. intermittent crank-no start. Replaced crank sensor due to code 1-3-1. May have been false code from crank/no start/stalling.
6. degraded engine bay wiring. Repaired failed wiring with new Volvo terminated leads.



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I bought this car with an intermittent crank-no-start condition. It would also throw a persistent check engine light when it was running.


It is consistently throwing codes from ECM port 2. NO CODES on the EZK port 6. (1-1-1)

3-1-2: Signal missing for knock-related fuel enrichment

2-1-3: Throttle switch full load setting faulty or grounding short

2-2-1: Fuel trim (lambda control) too lean at part load



Here are the pics of the car:


ZVOLV

Thread '1990 740 GLE 16V'

image1 (1).jpegimage0 (1).jpegimage8 (1).jpegimage7 (1).jpeg
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Duplicated the crank no start again yesterday. I need to get a good wiring diagram.
 
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If you don't see a recently replaced CPS, start with that. A lot of the symptoms you describe are common with a failing sensor. They are cheap and working or not, it is the first part I replace on any LH 2.4 or LH 3.1 2/7/9 as soon as they come in to my possession if it hasn't obviously been already done.
 
312 code might mean it's not seeing the knock sensor.
213 means it's having an issue with the full throttle part of the throttle switch. LH2.4 n/a uses an idle switch and full throttle switch.
221 I'd say is a vacuum leak.
 
LH 2.4 will barely run without the knock sensor signal. I found that out when I did a head gasket on my 940 Turbo and forgot to hook up the connector when I was finishing the job.
 
ZVOLV said:
It is consistently throwing codes from ECM port 2. NO CODES on the EZK port 6. (1-1-1)
3-1-2: Signal missing for knock-related fuel enrichment
2-1-3: Throttle switch full load setting faulty or grounding short
2-2-1: Fuel trim (lambda control) too lean at part load
Click to expand...
2-1-3 means the ECU is seeing WOT (TPS WOT switch closed to ground) when at idle/light load. Check the voltage on the TPS pins.
3-1-2 is a problem in the EZK to ECU knock enrichment wire - maybe a poor connection, or maybe poor power/ground to the EZK.
 
I try to always use the correct terminal test probe whenever I front-probe a terminal. I also am checking terminal tension at the same time.

I need to find which probes are the correct ones for 1991 Volvo 740. Suggestions? Anybody know what size the Bosch terminals are underhood and at the EZK/LH boxes?

I can always make my own probes by cannibalizing some old parts for their terminals, I may just do that.
 
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Ok so I found a torn FPR regulator vacuum elbow. I tore the end off and "fixed" the leak temporarily and then reset the battery. I got a good solid 750 rpm in-gear idle for a while after that. I drove it around the parking lot, never floored it, then the same codes came back, no WOT throttle was ever applied. The idle started getting low and shitty again, but power and idle improved after fixing the FPR vacuum leak.

Idle on startup is 1500 rpms now. Then I blip the throttle and it goes back to "normal" for the rest of the key cycle.

bobxyz said:
Pins are 2.8mm wide by 0.8mm thick. If you have a salvage yard nearby, just cut off a stereo speaker connector pair.
Click to expand...

I just ordered a set of male and female 2.8x0.8mm terminal test probes.

What about the EZK/LH terminals? Are they the same size?
 
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Almost all the connectors use the same pins, including EZK,ECU,injectors,TPS,CPS,IAC,Knock,O2heater. On the 240s, the engine-harness-to-cabin-harness,speakers,and other harness-to-harness connectors too. I don't know about the other 740 harness-to-harness connectors.
 
I am getting strange 02 sensor voltage readings.

TPS checked out good with the meter. Opens and closes the idle switch normally. Opens and closes the WOT switch. Voltage readings seemed normal.

Unplug the TPS and the idle shoots to 2000 rpms.
 
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I got the engine fully warmed up this morning by ripping it up and down the neighborhood. 16V high rpm glory!!!

I returned to base and double checked my 02 sensor voltage, now it is pegged at 0.9V. IDK if it is a true reading or a bunk 02. Bosch 02 sensor ordered.

I removed this homemade jumper wire that was inline with the IAC connector. Somebody may have put it in there to test the IAC voltage readings...IDK.

IACjumper.jpg
 
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Corroded terminals for two relays at the expansion tank. One must be the radio interference suppression relay (powers injectors). Hopefully this is the intermittent crank-no-start fix.

CorrodedTerminals.jpg



The good news is the engine is a VOLVO reman/new engine at one point. No oil leaks found yet. Here is the phantom connector that may not go to anything:

looseConnector.jpg
 
ZVOLV said:
Corroded terminals for two relays at the expansion tank. One must be the radio interference suppression relay (powers injectors). Hopefully this is the intermittent crank-no-start fix.

View attachment 32924



The good news is the engine is a VOLVO reman/new engine at one point. No oil leaks found yet. Here is the phantom connector that may not go to anything:

View attachment 32926
Click to expand...
I have the same thing in my 940, I believe that spare is for EGR you don't have.
 
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