[Braingears]

I'm running the M104 straight six. When I floor it, the engine starts to rev up, then hesitates randomly.
If I let up on the accelerator just a little, I get the full power back.
It's got new plugs, new wires, and one new coil. I don't know what else to check. It only happens when the accelerator is all of the way down, but does not matter if I am pushing the kick-down switch.

Chuck

 

[Brent]

How did the wiring to the coils look when you replaced it? I had to replaced the engine wiring harness to cure the ills my truck seemed to have from the day I got it. Nobody could ever seem to figure it out, including the dealer. I had a coil fail, replaced it and it failed again. I took a good look at the wiring and it was brittle and flaking off. After replacing the harness (not too hard) it has never run this good.

 

[ewalberg]

any time i hear hesitation under throttle and it makes me think the fuel filter is getting clogged. If you go on long drives does it get worse? I had that experience.

 

[w.james]

I would change the fuel filter first too

 

[Braingears]

The symtoms are not fuel relateded. I changed the filters six months ago too.
It seems either electrical (possibly computer???) or something with that air flap.
When I got the truck, one of the three coils were bad. I replaced the coil and while I was at it; I replaced the plugs and the wires too.
When it hesitates, it is not the same as a cylinder not firing. Nothing quite that dramatic.
There have been no computer codes via ODB-II. Other than when I "floor it", she is perfectly smooth.

Chuck

 

[GUIMO]

I have been dealing with the same problem for the last three weeks until finally my mechanic got with the problem, he said it had to do with the air flap and "piston" (which i am not sure what it is). Fortunately I didn't have to replace anything, he just calibrate that thing, it took about two hours to do that. I hope it helps you.
Good luck

 

[Braingears]

GUIMO - 2/14/2005 7:07 PM

I have been dealing with the same problem for the last three weeks until finally my mechanic got with the problem, he said it had to do with the air flap and "piston" (which i am not sure what it is). Fortunately I didn't have to replace anything, he just calibrate that thing, it took about two hours to do that. I hope it helps you.
Good luck

Yea,
My mechanic had me look in the same area. He had me remove the air flap and check to make sure that the assembly was tight (no play). I have not thought of calibrating it.

Chuck

 

[fourbyfourclub]

Hello How I unerstood you have 1998 G320 with 104 engine.
It is a good advice to check "air flap" or "piston"
but these parts not exist on your engine.
Engine electric harness is a common problem but, if it is bad car will misfire in an idle.
Try to retrive any OBD codes.
Try to disconect Air Flow electric plug and see if any difference.

 

[Braingears]

fourbyfourclub - 2/16/2005 9:08 AM

Hello How I unerstood you have 1998 G320 with 104 engine.
It is a good advice to check "air flap" or "piston"
but these parts not exist on your engine.
Engine electric harness is a common problem but, if it is bad car will misfire in an idle.
Try to retrive any OBD codes.
Try to disconect Air Flow electric plug and see if any difference.

There are no ODB-II Codes. The only two things that I can see this being is one of the wires grouding out, or the air flap closing (electronically - if that is how it's controlled).
It only happens under these conditions:
1. When the pedal is to the floor
2. around 3500RPM to 5500RPM
3. It will rev up full range in 1st or 2nd gear flawless. Then will "hesitate" in 3rd gear.

These are the reasons I keep thinking there might be some electronic or computer thing going on.

Chuck

 

[Brent]

I think that making a blanket statement about how the engine will react to a bad wiring harness is a bit of a mistake. Mine ran poorly for three years before it got so bad that the fix was obvious. That harness controls the electronic fuel injector firing as well as the ignition system. Mine did not idle poorly but it sure lacked power.

There is one other possibility though I don't know how to check it out. There is a cam advance that happens at 3500 rpm. Since you mention that as a starting point for your problem, maybe it is worth checking out. The intake cam is advanced at that point to allow better high end breathing. If it doesn't, who knows...concievably a loss of power as the ignition and FI curves are now not in synch with the cam timing and valve events. This system is also hooked into the engine wiring harness.

Have you taken a close look at some of the wiring in and around the coils and injectors? I really think it is worth some checking.

 

[Brian]

I think Brent is on the right track here. I have a 1995 E320 with the M104 engine and the same symptoms (it makes me feel fortunate to have the M103 engine in my 300GE). I have had no luck in diagnosing the problem and am going to start over again using Brent's suggestions.

Here is what happens with my vehicle: hesitation under moderate or hard acceleration throughout the power band. I can feel the cam advance around 3,500 RPM, but lots of sputtering with any heavy use of the right foot. The most dramatic problems occur when driving up mountain passes when I manually downshift into 3rd gear and step hard on the gas to keep moving. Sometimes the engine will cut out so abruptly it feels like a rev limiter kicking in, even though the engine is nowhere near redline. The vehicle will lurch for a moment, then pick back up again and continue to accelerate. I've had the fuel system, injectors, and all the usual suspects examined with no luck. The car runs perfectly (quick startup, smooth idle, etc.) except under hard acceleration. I'm wondering if the fuel pump might be part of the problem and may not be delivering an adequate fuel supply because it is buzzing quite a bit and might be on the verge of failure. I'll post any results if I get this figured out.

 

[Brent]

Fuel pressure should be easy to check. There should be a test port on one of the fuel rails you could fit a gauge to. Any import shop could do that test as well. It might take a chassis dyno along with the fuel pressure gauge to prove or disprove the theory under load. An old fashioned "scope" might also tell you what is happening to the spark under load on a dyno as well. Of course by now you have blown $3-400 just figuring it out without having fixed anything [B)]

I can't restate it enough, I chased drivability problems for YEARS on that truck. I did plugs wires fuel injector cleanings, replaced the expensive M114 motor under the intake. I had several mechanics, even shop foremen in large dealerships try and figure it out. Replacing that harness made it like a new car again. I thought that by '98 the harness issue was fixed but with Europas imports, the '98 could very well be a '97 MY production.