Volvo 740 Idle and Stalling Issues

Ryan911T · Post by **Ryan911T** » 14 Nov 2017, 08:07

I've been trying to figure out what is wrong with my 1986 Volvo 740 GLE with the B230F with the M46 gearbox.

So, it would always misfire in the rain until it warmed up. Ran like that during some heavy rain for a few days, then it was dry. During start up it would idle around 1.1K and the revs would go up and down, almost sounding like a diesel engine as well. This happens when it's been sitting for a while and is cold. When it is warm, it will idle around 800-900 RPM and not make that diesel-like idle sound. It still doesn't sound normal, however. While driving through it doesn't feel right. In gear around a corner at low RPM under load, it will misfire.

So, I replaced the spark plugs, wires, and installed a new distributor cap. The contact points on the old one were pretty dirty. I also cleaned the MAF to be safe with electronics cleaner. After cleaning the MAF, it would stall while coming to a stop. While driving and coming to a stop, I'd push the clutch in, the RPMs would drop, and it would stall. This only happens half of the time when it is warmed up. Still runs rough. The old spark plugs were pretty dark and a friend told me it looked like they were running hot, which could be from running rich.

I'm not sure what to try next. I tested the fuel injector O-rings by spraying WD-40 around them while it was idling rough to see if there was a leak and nothing changed. I can sometimes smell fuel in the engine bay when I manually open the throttle.

Filled up with 91-octane (the only available non-ethanol fuel) and put some seafoam in the tank to clean the injectors. Tried running a bottle of HEET dry gas, nothing. Cleaned the tube running from the MAF to the TB. Got a bunch of grime out. Cleaned the outside of the TB since I don't have the gasket to remove and completely clean. It was grimy on the inside (probably hadn't been cleaned in its 30-year existence). Still ran rough at idle and stalled. I sprayed electric cleaner on exposed connections just to be safe and make sure the connections were okay.

I'm running out of ideas as to what it could be. Any help would be greatly appreciated.

Thank you in advance.

Ryan911T · Post by **Ryan911T** » 14 Nov 2017, 14:48

Can hear a faint hissing somewhere, don't know what line. My guess is the little piece where two hoses (one large before the TB and one small after on the manifold) come together on a piece that connects to the engine block on cylinder No. 3. Any idea what that could be?

Ryan911T · Post by **Ryan911T** » 17 Nov 2017, 12:04

Could this old wire connecting to the coolant temp sensor be causing it to run rich?

Was wondering if this wiring was supposed to be some kind of ground. It's connected to the firewall on one end, and isn't connected to anything on the other (where I'm holding it). Would it be a ground for the distributor by any chance?

Post by **RickHaleParker** » 17 Nov 2017, 13:08

I thinking you may have a air intake leak that goes away or gets better when the engine warms up. This would produce the wrong air/fuel mixture and explain a lot of the symptoms. Get a can of ether (starting fluid). With the engine cold and running, spray the ether around the intake manifold. If there is a leak it will suck in the ether and your hear the engine surge. Also look for disconnected of damaged vacuum lines that are letting air into the intake after the MAF sensor.

Ryan911T · Post by **Ryan911T** » 17 Nov 2017, 13:50

Thanks, will try that this weekend. I'll attach that ground strap to the one valve cover bolt to see if that does anything as well. Couldn't find any vacuum leaks with the hoses. This is a 31-year old car that I've owned for three years. I only know the stuff that I replaced pretty much, so it could be a wide range of things. Thanks for the help!

lummert · Post by **lummert** » 17 Nov 2017, 15:09

Ryan911T wrote: ↑17 Nov 2017, 12:04

Could this old wire connecting to the coolant temp sensor be causing it to run rich?

Was wondering if this wiring was supposed to be some kind of ground. It's connected to the firewall on one end, and isn't connected to anything on the other (where I'm holding it). Would it be a ground for the distributor by any chance?

The ground strap probably connects to the rear cam cover hold down stud and nut.

Post by **RickHaleParker** » 17 Nov 2017, 17:31

Couldn't find any vacuum leaks with the hoses.

Use the Ether to check the connections and the hoses also. The Ether can find stuff you cannot see.

Ryan911T · Post by **Ryan911T** » 18 Nov 2017, 13:37

Sprayed ether around the manifold gasket and virtually every hose I could find after the MAF. Used an entire bottle and nothing. No engine surge or change in how it idled.

Attached that ground wire to the cover stud and nut and that fixed the engine interference that I would hear when I had the AM radio on. Back to square one.

Post by **RickHaleParker** » 18 Nov 2017, 16:18

Your correct when you said "This is a 31-year old car .. it could be a wide range of things" I think your on a jorney like I had with my S90/960. I had to recondition a number of systems before I got the engine running right.

Before the days of coil packs, misfire when raining was a common problem. It was moisture or humidity getting in cracks in the ignition system, causing arc overs. You have new points, wires and cap. The only two components left are rotor and ignition coil. Inspect the two for the slightest crack, it does not take much for them to arc over. The old time road service guys call this the golden years ... they made quite a bit of money off this.

Your friend is correct, dark spark plugs can indicate an overly rich fuel mixture. Was the color Tan/Gray, White Ash deposits, Yellowish Brown or Black. Were the deposits wet or dry? Solid black or speckled?

Possible causes for dark spark plugs.
1. Plug heat range too cold.
2. Plug gap too large.
3. Vacuum leaks.
4. Low compression.
5. Overly retarded timing.
6. Leaking fuel injectors, including internal leakage allowing unmetered fuel to pass.

If this was my project, I would do a compression test. Fully inspect the ignition system for cracks. Check the timing, make sure the correct plugs are installed and gaped correctly.

Ryan911T · Post by **Ryan911T** » 13 Dec 2017, 11:59

So, after playing around and trying to diagnose things, I started researching the fuel system online. Found a video that showed a bad fuel pressure regulator on a 240 and how to diagnose one. Smelled fuel in the hose that was connected to my intake manifold.

Just got the new part from FCP Euro today, installed it in about 15 mins, and voila! Runs perfect now. Just have to give it an oil change after all those misfires/stalling issues I had prior.