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Old 11-21-2022, 10:34 AM   #1
245gti
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Default 1990 740 16V Periodic/Random Injector Cut Out

Good day all. My wife's 740 has been suffering from this strange issue and the parts cannon hasn't managed to fix it. She came home one day saying the car was shutting off randomly, then would catch and run for a few seconds, then shut off and catch. This was random though. It would run fine for a few minutes, then cut out, catch, rinse, repeat. When it first did it while I was driving I made the determination it was a fuel issue, not spark, because there was never any popping in the exhaust when it cut, even at full throttle. I've had a spark cut issue and it feels and acts much differently.

First things first...fuel pump and relay are operating correctly and this isn't acting like a fuel pump issue where it will falter and hesitate. This is an on-off thing.

Initiate parts cannon. The first thing I did was replace the fuel filter, even though I suspected that would not be the problem. The old filter did have some restriction but there was no change with the new filter. I then noticed the wiring to the crank position sensor was badly deteriorated so I replaced the CPS. No change.

I then, with a little help from my friends, started checking the electronics. We found when it was acting up, we were losing the injector pulse...the injectors would just shut off. We checked continuity to all injectors and all was good. Because the injectors are fired through a grounding circuit we checked and cleaned all the grounding points. No difference.

Continue parts cannon. I thought perhaps the ECU was going bad so purchased 2 more correct ECUs and neither made any difference. I even plugged in a turbo ECU I had laying around and that made no difference either. I then changed the EZK box. No difference. I then bought a new ignition switch and put it in. No difference. I've replaced or bypassed every relay in the system that might have anything to do with fuel delivery. Nothing has made a difference.

I've got two of the smartest guys I know working on this and they are both stumped, as am I.

Just a little background on the car...I brought it in from Japan 7 years ago. At that time it had 24,000 km on it. No, that isn't a misprint. A few months after it arrived the odometer drive gear broke so I replaced the cluster with a junkyard one. I'm guessing it has about 100,000 km on it now.

What have I missed?
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Old 11-21-2022, 02:23 PM   #2
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My guess at the parts cannon would be a suspect mass air sensor. The other thought was bad connections or an intermittent ignition amp. If the system is missing spark you won't get an injector pulse. Check the various connectors for pins being pushed back or not making good contact
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Old 11-21-2022, 04:30 PM   #3
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My diagram shows a "radio suppression relay" that powers the injectors.
They have been known to fail.
Swapping with the one next to it (if you have one) on the right shock tower is the usual test.

It also shows you having a throttle position switch (idle / full throttle).
My "Regina book" says:
- The injectors are shut during engine braking.
- Fuel injection is switched off on over-run.

I assume this means if you're going down a hill with your foot off the gas, the "idle" switch is activated, and the system turns off the injectors until engine speed has dropped below a certain RPM.

If your switch is bad, or the wires are chafed and shorting, this could tell the system that you're at idle, when you're actually cruising along at 60 MPH.
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Old 11-22-2022, 02:20 AM   #4
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Same relay for ‘radio suppression’ (injector/iac/amm/ powers most anything that isn’t the fuel pumps themselves iirc or something like that on the 700 models?) & pusher fan, sure.
Easy to swap them &/or verify both power the pusher fan with switch(es) for it jumpered, but if you say you’ve bypassed all relays relating to the FI?

It’s uhh… LH2.4 & B234F engine same as our N.American 16V 7/9s?
It’s…RHD or LHD?

I’ve seen the crimp that gathers all 4 injector wires fail intermittently/defective from new & not holding the wires tight/quite gas tight & corroding slowly (they didn’t get it quite crimped right or route it quite right and iirc Japan is even stricter emissions than CA and those have an EGR extra temp sensor and some other emissions bull**** on the 1-off rare engine harness if I remember well?) once in a great while on engine harnesses w/uncommon options on the ‘90+ RWDs, but it’s rare?

I pinched the harness and really wiggled it with a substituted load and watched the test lamp dim on moms 96k mile 1993.5 244 w/aux fuse by the battery & unique 1/2 year engine harness.

I had another late late 1993.5+ 240 49-state model engine harness (No EGR or pulse air) & borrowed some aircraft crimpers and vinyl sheathing used off of other junkers and fixed it.

What a pain in the butt, but now it’s routed exactly like factory sans rando injector drop-out or brief fault code (which has nothing to do with the injectors themselves on primitive OBD 1 cars like ours usually..usually correct resistance or hooked up or not is all it knows to look for (if it codes at all without a license outright stall?) not electronic wave form signature of injectors firing like a more modern cars brainier diagnostic loop checks for better snd worse reliability & complexity /diagnostic ease-wise?).

I’ve only seen this on unusually optioned 1990+ models twice in 20 years and I dunno how many/lost count of how many beat to hell RWD Volvos fwiw? But I’m a hack and not an old school electronics wizard or experienced exorcist for a complicated eurotrash car?

I stick to pre airbag no options -‘89 145/245s for these reasons & a few others to mercilessly flog as defacto work trucks , but there are also reasons why the WAF (wife acceptance factor) may be low & a fella’s divorced?

On the no restart you’ve verified no injectors lighting the noid light?
I take it this is a warm restart attempt?
In what ambient temps or doesn’t matter?
I’ve had some coolant temp sensor connection shenanigans that don’t always code depending on ambient temp with a no immediate restart? Sometimes just corroded plug?

Idk about regina vs. LH but the RPMs must be >1100 for LH to totally cut the fuel with the TPS on the idling contact only…

It strikes me as improbable that the ECU is deliberately cutting injector pulse; as often if there’s an inaccurate or briefly intermittent RPM / CPS reading that’ll affect the spark &/or code or have other symptoms?

I believe regina is n/a 8v North American market 49-state (or Canadian even more lax emissions standards?) automatic 7/9 only?
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Old 11-22-2022, 08:50 AM   #5
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Quote:
Originally Posted by MasterBlaster View Post
My diagram shows a "radio suppression relay" that powers the injectors.
They have been known to fail.
Swapping with the one next to it (if you have one) on the right shock tower is the usual test.

It also shows you having a throttle position switch (idle / full throttle).
My "Regina book" says:
- The injectors are shut during engine braking.
- Fuel injection is switched off on over-run.

I assume this means if you're going down a hill with your foot off the gas, the "idle" switch is activated, and the system turns off the injectors until engine speed has dropped below a certain RPM.

If your switch is bad, or the wires are chafed and shorting, this could tell the system that you're at idle, when you're actually cruising along at 60 MPH.
I guess the relay could be bad but more than likely the problem is with the plug. The 4 pole plug insulation is gone and the pin wires come out, which in turn won't fire the injectors. If everything else is working, this is the likely cuprit. But 7/9 are notorious for wiring issues in other places.
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Old 11-22-2022, 08:52 AM   #6
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Originally Posted by 245gti View Post
Good day all. My wife's 740 has been suffering from this strange issue and the parts cannon hasn't managed to fix it. She came home one day saying the car was shutting off randomly, then would catch and run for a few seconds, then shut off and catch. This was random though. It would run fine for a few minutes, then cut out, catch, rinse, repeat. When it first did it while I was driving I made the determination it was a fuel issue, not spark, because there was never any popping in the exhaust when it cut, even at full throttle. I've had a spark cut issue and it feels and acts much differently.

First things first...fuel pump and relay are operating correctly and this isn't acting like a fuel pump issue where it will falter and hesitate. This is an on-off thing.

Initiate parts cannon. The first thing I did was replace the fuel filter, even though I suspected that would not be the problem. The old filter did have some restriction but there was no change with the new filter. I then noticed the wiring to the crank position sensor was badly deteriorated so I replaced the CPS. No change.

I then, with a little help from my friends, started checking the electronics. We found when it was acting up, we were losing the injector pulse...the injectors would just shut off. We checked continuity to all injectors and all was good. Because the injectors are fired through a grounding circuit we checked and cleaned all the grounding points. No difference.

Continue parts cannon. I thought perhaps the ECU was going bad so purchased 2 more correct ECUs and neither made any difference. I even plugged in a turbo ECU I had laying around and that made no difference either. I then changed the EZK box. No difference. I then bought a new ignition switch and put it in. No difference. I've replaced or bypassed every relay in the system that might have anything to do with fuel delivery. Nothing has made a difference.

I've got two of the smartest guys I know working on this and they are both stumped, as am I.

Just a little background on the car...I brought it in from Japan 7 years ago. At that time it had 24,000 km on it. No, that isn't a misprint. A few months after it arrived the odometer drive gear broke so I replaced the cluster with a junkyard one. I'm guessing it has about 100,000 km on it now.

What have I missed?
How come they didn't check the radio suppresion relay? Are they Volvo guys? Mainly the plug to relay but the relay could be bad but unlikely.
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Old 11-22-2022, 10:35 AM   #7
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How come they didn't check the radio suppresion relay? Are they Volvo guys? Mainly the plug to relay but the relay could be bad but unlikely.
I did say we've swapped and/or jumpered every relay related to the FI. This would include the RSR. And yes, they're both Volvo guys. Some of the old guys here will remember one of them...Matt Dupuis. They're both 240/740 guys.
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Old 11-22-2022, 01:23 PM   #8
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1) When has it cut out? Cruise-only? At idle? Coasting down? Accelerating?
2) Does it have a tach? If so, what does the tach do during cut out?
3) Any diag codes after cut out?
4) LH2.4 or Rex/Regina? (I'd expect LH2.4, but if not, Regina has a MAP sensor to consider)

If the CPS is completely bad, the EZK won't get a good signal and won't try to fire spark and won't generate a tach signal. Since the EZK sends the main tach signal to the ECU, no tach signal will result in no fueling from the ECU.

If the CPS is failing, the EZK might get a good-enough signal to generate a wrong-speed tach and mis-fire spark. Fueling will be wrong due to wrong tach rpm speed.

If the power stage is failing, you'll have good tach, correct fueling, but bad/intermittent spark.

Failing MAF will have good spark but bad fueling.

If the cut out has ever occurred during idle, I'd try wiggling every wire/harness that you can get to while idling and see if there's any cut out.
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Old 11-24-2022, 08:37 AM   #9
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Quote:
Originally Posted by bobxyz View Post
1) When has it cut out? Cruise-only? At idle? Coasting down? Accelerating?
2) Does it have a tach? If so, what does the tach do during cut out?
3) Any diag codes after cut out?
4) LH2.4 or Rex/Regina? (I'd expect LH2.4, but if not, Regina has a MAP sensor to consider)

If the CPS is completely bad, the EZK won't get a good signal and won't try to fire spark and won't generate a tach signal. Since the EZK sends the main tach signal to the ECU, no tach signal will result in no fueling from the ECU.

If the CPS is failing, the EZK might get a good-enough signal to generate a wrong-speed tach and mis-fire spark. Fueling will be wrong due to wrong tach rpm speed.

If the power stage is failing, you'll have good tach, correct fueling, but bad/intermittent spark.

Failing MAF will have good spark but bad fueling.

If the cut out has ever occurred during idle, I'd try wiggling every wire/harness that you can get to while idling and see if there's any cut out.
Wait a minute, isn’t the tach taken off the coil - on 2.4 cars same as all the other RWD gas Volvos (except 960 / coil on plug models?)…
…(can modify the gasser tach to work on the diesel alt terminal for 200 series that never got factory diesel tach &/or VW/Audi gasser also with VDO instruments sans tach for us electron ignorant, diesel dork/tweakers that are electron-superstitious & fearful aspiring mech-e & chemistry types, but that’s another story…)

My experience is the tach can and does have incorrect reading if/when the powerstage is flaking out/failing intermittently?

The rest looks well written, accurate/correct, helpful & to the point.

But if the OP is saying spark, fuel pumps & no injector pulse, that’s a bit of a riddle other than uhh…wiring/gathered crimp for injectors/batch fire on the ECU/injector driver ground side, which I have seen before, but it’s been exceedingly rare?

Or, just, exceedingly short/weak injector pulse from a way out coolant temp or air mass reading, but depending on how long it occurs/recurs & when or how, I’d expect a code &/or other symptom(s)?

If Matt’s stumped, it’s a riddle no doubt, but I’d also imagine he has limited time with kiddo to come over remotely & might easily get too deep into the hard stuff or correct diagnosis methods when maybe it’s something stupid & basic…once it can be found…
Need an exorcist or wizard for these eurotrash cars, especially the more complicated electrically laden more luxurious models…

Carry on, bobxyz & cleanflametrap know more about electrical than I ever will no doubt, tho both have 200 series/more 200 chassis experience & little/no 7/9 I believe much less furrin’ market 7/9?

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Water proof/sealed 3.5mm bullet terminal clear coating shoulder not staying in the plug going to **** is only an issue in the dirty south like TX &/or higher mile oil leaky cars with heat, oil and UV.

I’d literally never seen that issue on meticulously maintained garaged Seattle & northward marine climate low UV high lattitude cool cloudy climate cars that ran well and had no Oil leaks until I picked the AZ & CO junkyards as an aspiring retired snowbird.

The sealed bullets were probably seen as an upgrade / logical appropriation of an extant GM wearherpak / VDO sealed terminal design concept as compared to unsealed spades that the -‘79 Volvos had in most locations in the engine bay prior (sealed bullets on the fuel pump under the car starting in ‘74 IIRC?) in salted roads or coastal northern climates to the Swedes sourcing their own funky VDO/German moral equivalent of a GM wearherpak (but kinda more serviceable & easier to see the wire colors going into the individual sealed bullets & ability to use different shape & # terminal plugs from 1-8+)…

…in time it became an issue, tho Volvos don’t like hot weather and I’d argue people rarely bought RWDs/Swedish imports in the dirty south en masse in those years, anyway, so why bother to cater to that clientele?

& they probably lasted the warranty and statute of limitations for implied warranties & strict USA lemon laws for ~10 years even in hot climates on beat out leaky cars, so?
Not much fun to patch cleanly later, but…

Last edited by Kjets On a Plane; 11-24-2022 at 09:07 AM..
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