740GL engine problems

[maxim naumov]

hello everyone

I have a 16 y.o. Volvo 740 GL (no lambda sensor) that had already made
180K miles (290K Km). it is a very sturdy and reliable car, not rusty.
engine is B200E, Constant Injection System.

the only problem I am having with it is that it is misfiring badly on
idle. driving range is fine, no power loss, no twitching on
acceleration. idle is really bad though, I suspect the engine at times
is running on two cylinders. when heating up after cold start
(additional injector in action), seems to run much more stable, but once
warmed up, starts to misfire. afaics, exhausts smell petrol.

I checked the ignition system and replaced most of it - it is not to
blame for sure. recently I replaced the cylinder head gasket and other
gaskets that go with this procedure. compression is fine, even a bit
higher than the manual says.

I suspect either injectors, or fuel distributor or insufficient vacuum
in the inlet manifold. I tried taking injectors out to check fuel
atomisation, the engine won't start. perhaps I should have plugged the
injector hole to keep vacuum ?

any ideas ? is it common for these injectors to get clogged ? I asked
local injector cleaning specialists and they told me that they don't
clean this type of injectors. maybe I can clean them myself with a
little acetone ?

thanks very much in advance guys. I really like this car and don't want
to drive it to the scrapyard yet because of such a stupid problem.

/max

 

[Mike F]

hello everyone

I have a 16 y.o. Volvo 740 GL (no lambda sensor) that had already made
180K miles (290K Km). it is a very sturdy and reliable car, not rusty.
engine is B200E, Constant Injection System.

the only problem I am having with it is that it is misfiring badly on
idle. driving range is fine, no power loss, no twitching on
acceleration. idle is really bad though, I suspect the engine at times
is running on two cylinders. when heating up after cold start
(additional injector in action), seems to run much more stable, but once
warmed up, starts to misfire. afaics, exhausts smell petrol.

I checked the ignition system and replaced most of it - it is not to
blame for sure. recently I replaced the cylinder head gasket and other
gaskets that go with this procedure. compression is fine, even a bit
higher than the manual says.

I suspect either injectors, or fuel distributor or insufficient vacuum
in the inlet manifold. I tried taking injectors out to check fuel
atomisation, the engine won't start. perhaps I should have plugged the
injector hole to keep vacuum ?

any ideas ? is it common for these injectors to get clogged ? I asked
local injector cleaning specialists and they told me that they don't
clean this type of injectors. maybe I can clean them myself with a
little acetone ?

thanks very much in advance guys. I really like this car and don't want
to drive it to the scrapyard yet because of such a stupid problem.

/max

My first guess would be vacuum leaks. Start with the boot from fuel
distributor to throttle body, then everything connected to the intake
manifold. This type of fuel injection bakes the seals that go between
the injector holders and the head, that's a common problem.

--
Mike F.
Thornhill (near Toronto), Ont.

Replace tt with t (twice!) and remove parentheses to email me directly.
(But I check the newsgroup more often than this email address.)

 

[Zeke]

Hi Mike,
It is very possible that it could be your idle air motor. It is
cylendrical about 1 1/2 inches, and about 5 inches long. it has an
electrical connection at one end and 2 connections for hoses (about
1/2" inside diameter), one in and one out. The "in" hose attatches to
the air intake plenum, post air flow sensor/pre throttle body. The
"out" hose attaches to the intake manifold, post throttle body. Use a
hose pincher, or a pliers and a couple of pieces of wood to block air
flow through this loop(preferably, post idle air motor.) if idle
changes, especially if it drops/stalls, this is not the problem, or the
Idle air bypass valve should be adjusted. This valve is the large thumb
screw located below the throttle body. If adjusting this valve with the
hose clamped seems to help, then it is just out of adjustment. It
should be adjusted until the idle is 500 rpm with the hose clamped. If
no change occurs, you may want to disassemble the idle air motor
mechanism and clean it with BRAKE PAD CLEANER, nothing that leaves a
petroleum residue. IE engine brite etc. that stuff will mess it up.
For more detailed instructions about this part, jot a line back, and
I'll tell ya' how to clean it step by step.

regards, and best of luck,
-Zeke-