760Turbo Idles Fine, Hesitation under Load

Mar 2nd, 2006, 16:29

Maybe you guys can help me. This is my first Volvo '88 760 Turbo. It has this strange problem.
It will Idle fine, nice and smooth. But under any load it intermitently has small Studder, Hesitation (backfires?).. For example: It Idles smooth at about 800RPM, While in Park I get the RPM's to about 2000, then it begins to cut out It will drop to 1500 suddenly then back up to 2000. Over and over. Very Intermittant, Some days is better than others... Does not seem to do this while coasting. More pronounced going up Hills ETC.

I recently replaced the entire Distributor, Plugs (did not check Gap), Wires, FI relay, Middle and Third Muffler (did not use Volvo or OEM, used similar sized parts), Belts, And most importantly the Fuel Pressure Regulator (<--This fixed a problem where it wouldnt start when hot).

May be coincidence, but problem did not appear untill after I replaced the exhaust, also i removed a clamp from FI rail, wiggled an injector,replaced clamp, Installed belts, Then i noticed this problem.. this may all be coincidence.

I tried swapping Radio Suppresion Relay, didnt help. Tried spraying Ether around Injector seats, No audible difference. 2 grounding Straps from the Firewall were attached to a Valve cover Bolt, (I moved 1 strap to the Fuel Rail) this did not help.

Any advice or Ideas would be much appreciated.

--Aaron

I may be on to something: I disconnected the Harness from the Air Mass Meter while at Idle. The Idle got a bit choppy, But when I take RPM back to 2000 it no longer hesitates. I then Reconnected the AMM and the problem is gone.... Perhaps bad connection? or disconnecting and reconnecting reset something... will keep you posted..

Mike_Brace · Mar 2nd, 2006, 21:56

Before I got to your post script I was thinking along the lines of AMM - had a similair problem with my 240 turbo. It would be useful if you could see your lambda readings and what they are doing when the problem occurs - I suspect it is going very rich (reading will be close to 1 volt if it is). On my a recon unit was even worse, it was sent back faulty but new unit was the same. The problem sorted itself with a good secondhand unit.

Mike

Mar 3rd, 2006, 12:50

Thanks mike,

I did place an order for a rebuild AMM, unfortunatly it will be 7+ days until arival. And I am impatient.
Im going to attempt to clean, what i believe is my current Faulty AMM, Using Injector cleaner, Electrical cleaner and Q-Tips. I also modified my Air Filter Housing to Only allow cold air in.

Has anybody had luck in cleaning an AMM? or when it malfunctions is it usually burnt out? mine ends with #007,

--Aaron

Mar 2nd, 2006, 16:29	#1
ajerviss Guest Location:	760Turbo Idles Fine, Hesitation under Load Maybe you guys can help me. This is my first Volvo '88 760 Turbo. It has this strange problem. It will Idle fine, nice and smooth. But under any load it intermitently has small Studder, Hesitation (backfires?).. For example: It Idles smooth at about 800RPM, While in Park I get the RPM's to about 2000, then it begins to cut out It will drop to 1500 suddenly then back up to 2000. Over and over. Very Intermittant, Some days is better than others... Does not seem to do this while coasting. More pronounced going up Hills ETC. I recently replaced the entire Distributor, Plugs (did not check Gap), Wires, FI relay, Middle and Third Muffler (did not use Volvo or OEM, used similar sized parts), Belts, And most importantly the Fuel Pressure Regulator (<--This fixed a problem where it wouldnt start when hot). May be coincidence, but problem did not appear untill after I replaced the exhaust, also i removed a clamp from FI rail, wiggled an injector,replaced clamp, Installed belts, Then i noticed this problem.. this may all be coincidence. I tried swapping Radio Suppresion Relay, didnt help. Tried spraying Ether around Injector seats, No audible difference. 2 grounding Straps from the Firewall were attached to a Valve cover Bolt, (I moved 1 strap to the Fuel Rail) this did not help. Any advice or Ideas would be much appreciated. --Aaron I may be on to something: I disconnected the Harness from the Air Mass Meter while at Idle. The Idle got a bit choppy, But when I take RPM back to 2000 it no longer hesitates. I then Reconnected the AMM and the problem is gone.... Perhaps bad connection? or disconnecting and reconnecting reset something... will keep you posted.. Last edited by ajerviss; Mar 2nd, 2006 at 17:29.

Mar 2nd, 2006, 21:56	#2
Mike_Brace Former contributor Last Online: Jul 2nd, 2022 07:54 Join Date: Dec 2004 Location: Rhosgoch, Anglesey	Before I got to your post script I was thinking along the lines of AMM - had a similair problem with my 240 turbo. It would be useful if you could see your lambda readings and what they are doing when the problem occurs - I suspect it is going very rich (reading will be close to 1 volt if it is). On my a recon unit was even worse, it was sent back faulty but new unit was the same. The problem sorted itself with a good secondhand unit. Mike __________________ A Volvo is for life not just for Christmas!

Mar 3rd, 2006, 12:50	#3
ajerviss Guest Location:	Thanks mike, I did place an order for a rebuild AMM, unfortunatly it will be 7+ days until arival. And I am impatient. Im going to attempt to clean, what i believe is my current Faulty AMM, Using Injector cleaner, Electrical cleaner and Q-Tips. I also modified my Air Filter Housing to Only allow cold air in. Has anybody had luck in cleaning an AMM? or when it malfunctions is it usually burnt out? mine ends with #007, --Aaron

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)