Sounds to me like you have the #3 and #4 wires on the wrong spark plugs.

If the spark plug isn't firing on a compression stroke, of course nothing will happen. From the left to the right (as you're facing the front of the engine) the order should be 4-3-1-2.

--
alex

'89 765T, 173,4xx mi

I'm thinking "pre-pump" (you said so yourself) and possibly an intake gasket. Spray carb cleaner all along the intake gasket...your car will alert you if there is a leak.

Chris

you mentioned in your post that your in tank pump was not working.
THAT IS YOUR PROBLEM. GOOD LUCK

Had a similar problem with my 240 Volvo - turned out to be a corroded cap and/or bad rotor. Replaced cap and rotor for $10, and car started and ran like new. Can also be your plug wires - check for continuity and correct resistance. Carbon cores often break or degrade over time. Replace with good quality wires.

You say you are getting spark at ALL plugs. That would cause me to direct my thinkingaway from things like distributor cap, rotor, and plug wires. It could be bad plugs, but that is easy to confirm by swapping them with functioning cylinders.

If there is a problem with intake-associated items like the AMM, vacuum hoses, brake booster, etc. it seems to me it would affect all cylinders.

Before you throw a bunch of money at new parts, you might want to check the compression. It almost sounds like you've got a head gasket leak between #3 and #4.

Another possibility is a leaking intake manifold gasket. You could check that the intake manifold nuts are all snug. You can also squirt a little oil around the gasket at the #3 an #4 intake runners to see if it temporarily smooths the idle.

I diagnosed my suddenly rough running, low power B230 this way. Immediately after a cold start, I went around and felt each exhaust manifold pipe next to the engine block. Three were getting warm right away. One wasn't. My problem turned out to be one bad spark plug wire. Seems like your problem is different, but it does seem interesting that two cylinders seem to make no difference when disconnected. Maybe this test will tell you whether you are really getting combustion in them or not.

Good luck.
--
Andy in St. Paul, '91 745 Regina 188K mi, '89 244 137K, '87 245 RIP

I do not have near the experieance as some of the others here... but spark or no spark, if you can pull a plug wire and the idle does not change that sounds like a clue to me...I did get a bad "Blue Streak" distributor cap once and it took me 2 weeks to figure it out. Bosh only now...

I'd double check the cap, rotor and the wires. I would think pulling a plug wire off should make it worse no matter what was wrong elsewhere.

"Cleaned throttel body and amm " I hope it was just the connections on the AMM, it is my understanding they do not respond well to ANYTHING going inside them other than air...
Bret
--
rust free in west Texas

have you checked your brake servo unit and its vacuum hose? reading your message where you say about rear cylinders...
--
i prefer non-german cars

while the car is off, disconnect your amm. then start it up and see how it performs. if it performs the same as before then you probably have a amm. if you notice it's doing worse than before, then your amm was probably good to begin with.
--
Kenric Tam
1990 Volvo 740 base sedan (B230F)
My Volvo 'Project'

The radio relay is easy to check. Swap the cooling fan relay with it. See if anything changes.

chances are you have a bad amm, I just went through everything you did to find that it was the amm the whole time. I don't regret changing everything because now I have a new car and learned alot. Ebay has them for around 40 bucks. good luck