I am working on a 1989 Volvo 780 with the 2.3l Turbo and my issue is that it will crank and attempt to fire, but won’t start, although sometimes it will start, but it runs rough and dies almost immediately. it is getting too much fuel.
I am suspecting an idle air control valve or a coolant temp sensor right now.

Any thoughts?

Hello,
I also have a 1989 VOLVO 780 T.
We enjoy the car...and plan to take her out for fall foliage here in Vermont soon.
Have you inspected and measured the resistor pack on the driver's side inner fender? If not, I would extend to you to find it, disconnect the white connector and measure the impedance from each end of each resistor, off the cuff should measure 7 ohms...inspect the plug for corrosion and the tips of each resistor.
Contact me for photos since I/We cannot upload.
Best,
Paul (VTV745T)

Before people jump in here saying it's the CPS (rpm sensor), which is a common cause of no-starts, your '89 780 with B230FT should be LH 2.2 with EZ-117K ignition that uses a Hall Effect sensor for timing advance and rpm sensing. Only the B230F NA switched to LH 2.4 in 1989, along with the newly introduced DOHC B234F. The B230FT became LH 2.4 in the next model year.

IMO, it likely isn't the idle air valve or block temp sensor. The idle air valve controls idle rpm by altering the amount of intake air bypassing the almost closed throttle plate. It's all metered air (comes from the AMM) and doesn't affect mix or combustion, just rpm. A bad block temp sensor usually doesn't affect starting, but typically causes high idle rpm and rough, rich running.

If you're sure it's excess fuel, as in unburned fuel, then my first guess for a badly intermittent no-start would be the ignition side, not the fuel side.

Does the tach needle jump during cranking? If not then likely the Hall sensor. Have you checked for spark? Note if a strong or weak spark or if only one plug sparks. Prime suspects will likely end up being the distributor (badly worn cap/rotor or more likely a bad Hall sensor) followed by ignition wiring (most likely coil to distributor).

To lead you through the ignition side diagnosis, read the FAQ here
https://www.brickboard.com/FAQ/700-900/ElectricalIgnition.htm#CarWontStartIgnitionDiagnosis


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Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now

with more testing i have been doing i found that if i let the car sit for a while with the spark plugs out, then when i put it together and start it, it runs.
when it runs it runs rough during the first 30 seconds of running, and then smoothes out and runs great. if i shut it off and try to restart it, it won't even attempt to fire.

i found out that i think there is oil getting into the combustion chamber and mixing with the gas, therefore not firing. it is a rebuilt motor, but the block was not machined, but should have been.

Let's say it is indeed too much fuel. Pulling the plugs, finding them wet, it will start again once you evaporate the excess fuel in the manifold and cylinders. Instead of jumping on the electronics, check the fuel pressure in the rail. Check for fuel in the vacuum line to the fuel pressure regulator.

Yes the temp sensor in the head (not block) for the LH2.3 system can be open circuit and cause fuel enough to start in the Yukon but flood it in Texas. Do a simple resistance measurement if you know the fuel pressure regulator is doing its job.
--
Art Benstein near Baltimore

"I don't want to retire. I'm not that good at crossword puzzles." -Norman Mailer

+1 on checking the fuel pressure regulator vacuum hose for fuel. Years ago, a friend of mine had the same issue with his 740. Replaced the fuel pressure regulator. All good….

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Will I buy another Volvo??? We'll see....

Hi,

Right off the top take the idea of the engine block NOT being machined will make it run and then stop.
You need to put that thought over into a corner of your mind or even out back somewhere! 😊

If the engine was truly rebuilt by removing the pistons and replacing the rings can be quite normal.
The bores get inspected for size and taper and a tolerance is allowed over the piston size. In many cases on these blocks the metal is so good it’s all that’s needed. Just put back in a cross hatched swirl finish of the bore to help the new rings seat themselves and all is good for the block.

I agree with all Dave Steven’s historical statements that you are probably not getting too much gasoline but not enough air on start up. Interpretations can be interchangeable.

The IAC has to be wide open on start up.
Dave brought up differences in systems for the reason of not only ignition but the IACs could be different.
Later models have a spring return to closed and is only powered open.
The other older IACs will have three pins because they were powered open and shut.
In either one if it does not open you will have the same problem.

If ever you get it to firing it cylinders does the engine rev up and back down to an idle?
Both IACs have to demonstrate that performance or it is bad or at least sticking.
Putting you foot on the throttle can allow more air to clear the plugs of gasoline but at the same time you are defeating the startup mode of the ECU. The throttle switch gives you up in that you want to accelerate and you are getting more injection pluses. Not good!
Keep your foot off the pedal. Make sure the throttle switch is clicking to tell the ECU you want IDLE or a STARTUP mode.
With the ignition system working and it’s RPM signal can tell the ECU which one to do.

You are supposed to start the car with only your key twist and touch nothing!
If not it’s a sign that something is out of adjustment or failing otherwise!

You could have a hesitant fuel system relay or some old fuel pumps.
If it flooding that’s probably not the case.
Your statement of wet plugs puts things back it’s getting too much fuel but in actuality it’s not enough air!

Is this car you’re working on, from your first post, have a know history with you, prior having the engine out, that it all worked?
Big difference between it’s your car or a barn find with hearsay. 🫣🤫😊

Phil