Low power problem with my 2.6L 190e-Problem Solved
 

I have posted several posts and emailed several people trying to figure the low power problem in my 1993 2.6L 190e.

I rebuilt the cylinderhead with guides, stems and springs 3K miles ago due to excessive oil consumption. The oil level is holding prefectly at the full mark after 3K miles and the oil color is still about 75% clear. Spark plugs are still looking normal. The igntion wires are 1 week old. Cap and rotor have less than 15K and look good. All six injectors were replaced about 40K miles ago apperently for no reason as it did not solve the low power problem.
The car starts fine cold and hot and idles at about 750 rpm. The idle fluctuates with +/- 20-25 rpm and I can feel that. This issue did not exist before the cylinderhead rebuild.

Just before I start posting this problem, I did some extra tests.

1. Attaching a vacum gage to the intake manifold gives a reading of 14-15 psi fluctuating according to the idle issue.

2. When raising the rpm to 2000 rpm and holding there, the vacuum needle goes up to about 17 psi then down to 15 psi and holds there.

3. Turning the A/C on brings the vacuum to 10-11 psi and the car feels slugish when driving off a start or trying to pass a car.

4. An engine compression test has shown an exact reading of 185 psi for all 6 cylinders. Test was repeated several times with the same reading no less or more. Specification I believe is 170 psi.

5. I have checked just about all the vaccum lines in the engine compartment and all still fine. I have disconnected a few lines when I rebuilt the head as I kept the intake manifold in the car during R&R of head.

Other tests I did in the past month.

EHA current and duty cycle were +1-1.2 amps and 61-69%. I adjusted to about -2 Amps and 45% duty cycle. Thanks to Steve B. A slight improvement in power (The O2 sensor works as it should)

Ignition coil passed the resistance test per the MB manual.

I adjsuted the control pressure cable several times and still shifts hard and doesn't accelerate as it should. I beleive the hard shift is due to low vacuum.

OVP was replaced with new 2 fuses unit apparently for no reason as it did not help. I just had to clear that thought.

I don't have a check engine light in this car nor an O2 sensor light at the dash. Is this normal? or PO has removed it?

I don't know what else to do? Any recommendations before I take it to the dealer or an inde shop

I must say after the cylinderhead job, when I start the car and the engine fires, it make a sound like an exhust manifold gasket leak sound then disappear immediately and I don't hear it anymore. I can't tell where it's coming from. Again, only when the engine fires hot or cold.

I haven't changed the fuel filter yet and I have one ready for this coming weekend.

Thanks
Meza

Your vacuum readings are low. (BTW they should be in inches Hg. not psi). Does the engine have an EGR system? Your symptoms could be caused by a stuck open EGR vavle.

Duke

Sounds to me with the exhaust noise you're hearing that the timing is retarted. Make sure the marks on the camshaft and the balancer match.

Two excellent replies I did not think about! From experience, I know low engine vacuum is related to timing and I should have thought of that considering that exhaust sound at startups! I will remove the valve cover and check the alignment marks on the cam and crank. I will also use my timing light. I beleieve I have the specs.

About the EGR, I don't know how it could effect the low vacuum condition I have or drivebility! All I know is that it lowers NOx emissions buy redirecting some of exhaust gases back into the cylinders. The idea here is: If you lower the cylinder gases temperature, you will lower your NOx. The exhaust redirected by the EGR has H2O as a product of the combustion process and that what lowers the temperature in the cylinders. Anyways, How can I test it?
I will do some tests by this weekend and post results.
Thank you guys,
More suggestions are welcome..
Meza

The EGR valve should only open at part throttle cruise, which is the condition for maximum NOx production. It should not be open at idle or WOT. If it's stuck open it causes what is essentially a vacuum leak at idle, which leans the mixture and causes combustion instablility.

I don't have EGR on my '88 2.6, so I can't speak specifically to the MBZ EGR system, but the first thing to do is a manual test of valve operation. Apply vacuum to the valve diaphragm to verify its integrity and disconnect the exhaust feed line and test for flow with the engine off. EGR valves are normally closed with no applied vacuum to the diaphragm. If necessary, remove the valve for a visual inspection and bench test. EGR valves are fairly common failure items on older higher mileage cars - they live in a tough environment. Also, there will be a vacuum switching valve that applies vacuum to the EGR valve diaphragm. You should be able to find it by tracing the vacuum line. I suspect that the vacuum switching valve is commanded by the ECU, but not sure.

Another cause of low vacuum could be a clogged exhaust system due to internal catalytic converter damage or a collapsed muffler baffle, however, I would verify proper operation of the EGR system first.

Duke

I know this probably sounds like and almost stupid remark but - When was the last time You changed Your air filter?

A couple of weaks ago I thought my car was much to sluggish (1984 500 SEL) but after I changed the airfilter it was much better. The old filter didn´t look dirty and was only about a year old with maybe 5000 miles on it.

Good Luck,

Mikael Westerberg

When was the last time You changed Your air filter?
 

The air filter is 1 week old. After the cylinderhead rebuilt I bought 2 air filters that failed\broke. They were Hengst (sp?) brand. When I tried to stretch it, the rubber breaks immediately. They are too small or old stock. I finally got a mann filter that fitted perfect.
Meza

I have checked the timing with a timing light and EGR
 

Looking at the front of the car, the engine would rotate clockwise. When I aim the timing light at the vibration dampner, I see 10 at the TDC mark (for the sensor) and the OT mark is to the left of 10. So If I am not mistaking: It's 10 degrees advanced Before Top Dead Center (BTDC). Is this within specs?

I have applied vacuum to the EGR valve and it holds vacuum good. When I pull the vaccum line, I hear a popping noise which tells me the diaphram is not raptured and the EGR is good.

Meza

The timing is listed on the emission decal, and it's probably 9 degrees, so if you're reading 10 it's okay. On the M103 I find using a dial back timing light is the best way to check timing. Dial the 0/T mark back to the pointer and read the dial on the light. The pointer for timing and the TDC sensor are not along the same radial line. There is a radial dowel pin on the balancer that signals TDC as it passes the magnetic pickup.

Your data indicates that the EGR valve vacuum diaphragm is opening and closing the valve, but the valve could be leaking. Figure out a way to check that the valve itself is not leaking when it's closed.

A quick test is to apply vacuum to open the valve at idle. Degradation of idle quality and vacuum indicates that the valve is functioning, but it still might be leaky. When the vavle opens at idle the change should be very noticeable. If not, good chance the valve is leaking, which would result in poor manifold vacuum/idle quality and sluggish acceleration. You've got the classic symptoms of a stuck open or leaking EGR valve.

Idle vacuum at 700 in neutral should be about 15-16". Free-revving at 2000 it should be about 20".

Duke

Duke,
Thanks for your reply. I will remove the valve cover and spark plugs this coming saturday and set the engine to TDC in order to check the cam and crank marks. I think this would be the most accurate method. I went by three automotive part stores to get a timing light with a dial and non had one. I got tired of driving after leaving work. I had to use the one I have w/o dial. I will go by Sears on Friday to get one. I will do your suggested method to check the EGR. Thanks again and I will post results as soon as I have it.
Meza

Before you remove the cam cover and check the timing marks, I would recommend you remove and bench test the EGR valve.

The Sears dial back light is good. It's the same as the Acton. I bought one last year - my old light was shocking me more than flashing the bulb. Don't know how I lived without the dial back feature all those years.

Duke

Problem Solved
 

I finally solved the low power problem with the car that I experienced after rebuilding the head. It was found by accident. I finally had some time and decided to take the valve cover and check the cam and crank alignment marks. After turning the engine manually about 20 times. I noticed the marks align in some revolutions and not in others. I said what the hell, I'll just take the front timing cover and re-align everything again. I adjusted the crank to TDC and the cam aligned this time. I took the tensioner out and guess what I found? The chain was loose by one tooth on the side that has the straight guide. I knew immediately that's the problem. I pulled up on the chain and took all the slack on the right and moved it to the left. My timming chain is new and all timming guides and tensioner. No I know why the tensioner plug took a lot of force to screw in during the head assembly. It wasn't as bad this time. I put everything back, started the car and voila! It started and idled alot smoother. Took the car for a test drive and it had lots of power. It drove like a 2.6L should drive. Oh by the way, it shifts much smoother after the vacuum went up to a steady 16 in.Hg.
Thanks to everybody who helped me with this problem.
Meza:) :)