running rough under power

klar5020 · Post by **klar5020** » 04 Apr 2013, 10:06

I have a 94 940 that runs rough and has low power when accelerating. It doesn't use any oil or smoke. It seems to idle OK but when I slowly open the throttle, in the garage, there's a very slight hesitation it runs rough almost like it's misfiring. It seems like at certain speeds (RPM) it's more noticeable than others. It also has low power when driving around.

I though it was a head gasket or valves or something but the compression is good and even on all cylinders. I changed the cap, rotor, and plug wires and it seemed to help a little but not completely. I've been waiting for a check engine light but there is none. I also pulled the valve cover, just looking around, and when I did I broke a hose that goes from the exhaust manifold to the air box at the front of the engine. It's about 1" in diameter. I can't find any information on it.. I glued it back together but I'd like to get a new one. What is it?

klar5020 · Post by **klar5020** » 05 Apr 2013, 08:01

Here's a pic of the engine. It's the hose just behind the timing belt cover that goes over the valve cover. I broke the hose where it separates at the T above the exhaust manifold. I haven't seen it shown on any vacuum or emissions diagram I've seen. I taped it temporarily. I also noticed quite a puff out of the valve cover when the engine is running. Is that normal. I never noticed it before. One thing more to mention. Even though I haven't got a CEL I have checked the codes and they are normal.. I'm at a loss..

klar5020 · Post by **klar5020** » 05 Apr 2013, 11:54

Continuing my research I found that stuff is pulse air system. Some of those parts are no longer available so it must not be too important. I think I'll just take it off... I've got the vacuum line to the valve plugged . Didn't change anything.. Hoping I get an error code.

Vauts1800 · Post by **Vauts1800** » 06 Apr 2013, 15:30

Did you change the spark plugs? What did the old one look like?did this start suddenly or has it got worse over time?
You are ok to disconnect the pulse air system, usually it would leak exhaust gas from the valves. I have removed the valves and blanked them with small coins.

klar5020 · Post by **klar5020** » 07 Apr 2013, 15:25

i did replace the plugs. That was the first think I did. They looked OK. I checked the plugs again after I've been driving and they still look OK. The problem came on suddenly...All of a sudden it started vibrating, mostly under power. I thought it was misfiring so I thought it was the head gasket or valves. I took it to a shop and the guy said "most likely the head gasket" so I stopped driving it because I didn't have the money for the head gasket. I started driving it again and thought I look into it more.I checked the pulse air and it is puffing out of the valves.. so I'll just disconnected it. I think I'll just replace the EGR valve since I know it's been a while since it was done.

JerryC · Post by **JerryC** » 10 Apr 2013, 02:03

You have even compression... but what value? Is there any loss of oil or coolant that isn't explained by leaks etc? If not, and decent comp values, you don't need a head gasket. Too many mechs 'shoot from the lip' and say something just to seem like they know something.

Kirby J · Post by **Kirby J** » 10 Apr 2013, 19:00

This may not apply, but I had similar symptoms with a 93 940 Regina. It turned out my fuel pump (there is only one on the Regina) was not supplying enough pressure to the system. It would idle fine, and it would cruise alright, but it really did not like to accelerate. After doing most of what you have done, I replaced the fuel pump, and no more problems. I had thought that the FPumps on these things either worked, or did not work. I discovered that they can begin to fail without failing completely. Of course, there are some differences between a 93 and a 94, but it is something to think about. And I think it is cheaper than a head gasket.
Kirby J

klar5020 · Post by **klar5020** » 12 Apr 2013, 08:05

Thanks for the replies. I don't have any coolant loss or milky oil so I don't think its the head gasket either. The compression is 165 or so and all are pretty close but number two was a little lower than the rest. I decided just to look around for now. At 300,000 I should check some stuff. I bought the car with 185,000 and I don't think anything was done to it so I pulled the intake manifold to get to the EGR valve to check that. The valve is working OK but I found the vacuum line to is busted. I also found the throttle body, and manifold in general, filthy. Really dirty and gummy. I I'll clean that stuff up and see what happens. My concern now is why I didn't get a check engine light or error codes. If the EGR valve wasn't working shouldn't I have gotten a CEL? The computer did work at one time because I have checked the codes before for a previous problem. Right now I think I'm just going to go through the service manual and check the cleanliness and functionality of everything for all the service intervals.