Slow to accelerate, heavy gas useage

[Charly]

New to me, had it all checked out, new tires, new windshield, detailed in/out: 1988 300 SE, W126 i6 - finally drove it today - filled it full of premium gas and off I go.

First I notice, slow off the stop, gas pedal feels fat - I'm pressing on the gas, but slow to respond - once it starts, off it goes! I moved my seat up, but now my knees are knocking on the underside - so that can't work.

Second, I notice, didn't travel very far (70 km) but wow, did the gas gauge move to nearly a 1/4 tank less!

So wonder if the two are connected or just isolated.

Changed the air filter, running synthetic oil (as the previous owner did) premium gas and everything else checked out on the inspection.

Spark plugs were in excellent condition and high quality
Replaced the cylinder wires (old)
idle adjusted
Must prime to start, but seems to start easier and easier each time.

TIA for insight and ideas.

[Skippy]

Originally Posted by Charly

New to me, had it all checked out, new tires, new windshield, detailed in/out: 1988 300 SE, W126 i6 - finally drove it today - filled it full of premium gas and off I go.

First I notice, slow off the stop, gas pedal feels fat - I'm pressing on the gas, but slow to respond - once it starts, off it goes! I moved my seat up, but now my knees are knocking on the underside - so that can't work.

Do you mean the pedal is hard to press, or it just doesn't respond quickly when you press it?

Second, I notice, didn't travel very far (70 km) but wow, did the gas gauge move to nearly a 1/4 tank less!

So wonder if the two are connected or just isolated.

Most likely related.

Changed the air filter, running synthetic oil (as the previous owner did) premium gas and everything else checked out on the inspection.

Spark plugs were in excellent condition and high quality
Replaced the cylinder wires (old)
idle adjusted
Must prime to start, but seems to start easier and easier each time.

TIA for insight and ideas.

Please explain "must prime to start". I didn't think the gas models had a primer pump. Also, does the car smoke at all? If so, what color smoke and under what conditions. How does the exhaust smell?

[Charly]

Originally Posted by Skippy

Do you mean the pedal is hard to press, or it just doesn't respond quickly when you press it?

REPLY: BOTH actually, pedal hard to press and slow to respond from a stop ... once traveling it's very smooth.

Most likely related.



Please explain "must prime to start". I didn't think the gas models had a primer pump. Also, does the car smoke at all? If so, what color smoke and under what conditions. How does the exhaust smell?

REPLY: no smoke at all


REPLY: German mechanic (worked at MB there) said to pump the pedal a few times before starting it or hold the pedal down when turning the key. Works.

[DieselPaul]

They are most likely related but I would not take the movement of a 20 year old VDO gauge gauge as gospel. They seem to move at varying rates throughout the sweep.

High quality plugs, if they are resistor plugs it doesn't matter if they are made of gold, the car will never run right.

Pull a spark plug out and show us a picture of the writing on it. A lot of people ignorantly put whatever Bosch plug the parts store spec's for their Benz, not knowing that Bosch has superseeded a resistor plug over the correct one and while their loyalty to Bosch is adorable, its misguided. If you have resistor wires and resistor plugs, the car will never run right.

Has the fuel filter been changed recently?

[Charly]

Hey Diesel Paul,

The spark plugs are NGK.

Unsure about the fuel filter

Agreed the gauge may not be accurate.

TODAY suddenly ALL the dash meters are OFF:
No gas, no rpm, no speedometer, no heat sensor et al.

All these work fine:
Car starts, runs, Alpine radio/cd, sunroof, power locks and all windows, indicators, all variations of headlights, wipers .... HEAT and AC at all levels fine

Neither the antenna or rear sun visor will move up/down - apparently did so at beginning but not now.

Could any of this be fuse related?


The PO gave me his diagnostics report from December 2013:

1. His mechanic confirmed it starts hard (manual says to prime before turning key)

2. tested Fuel pressure - at spec of 80 psi at rest is 45 psi overnight dropped to 37 psi - all w/i spec

3. Coolant sensor, micro switches and Eha valve all at spec.

4. Test powers and main starting voltage is ZERO at Eha Valve. Test load reduction relay and is open circuit. Bypass and engine runs and starts normally.

5. Req a load reduction relay due to corrosion. Veh has new battery possible during boost it blew the corroded fuse in the relay. (he replaced Over Voltage Protection Relay)

6. Inspect state of tune, spark plugs new but wires don't hold on tips of plugs (I changed wires early August 2014).

7. Dist Cap is oil soaked and plug wells have oil in them, rotor is pitted, causing misfire, requires cap rotor wires and proper set up

8. Numerous oil leaks visible from top. Valve cover, timing chain covers, recommend shampoo and dye test for leaks (I changed valve cover and shampooed engine early August 2014 - no oil or other stains on ground under car after 3 days driving).

9. Says heater issues may be related to possible stereo installer knocking off a vac hose or power wire. Check Control Heads by removal of centre console (August 20, 2014 had med temp heat on low only - had a radiator co poke and prod + mechanic - said it could be air pockets &/or gummed up, flaps function fine. Suddenly came on full at all levels and had to turn it down it was blowing so hot, need to check floor flow)

So that's the history that I'm aware of - would any of this affect the dash meters?

TIA.

[86560SEL]

We have an '88 300SEL and have never had to "prime" it to start... just turn the key and it starts up at once.

These are not known as powerhouse cars, but should still not be considered slow. We had a problem with our actual accelerator before (pedal had broken at the floor) and it was difficult to depress. I ordered a new one from here and no more issues.

[Charly]

Thanks 86560SEL, mine is 4 to 5 times before starting, will check further into both starter and pedal.

[gatorblue92]

Originally Posted by Charly

Hey Diesel Paul,

The spark plugs are NGK.

Unsure about the fuel filter

Agreed the gauge may not be accurate.

TODAY suddenly ALL the dash meters are OFF:
No gas, no rpm, no speedometer, no heat sensor et al.

All these work fine:
Car starts, runs, Alpine radio/cd, sunroof, power locks and all windows, indicators, all variations of headlights, wipers .... HEAT and AC at all levels fine

Neither the antenna or rear sun visor will move up/down - apparently did so at beginning but not now.

Could any of this be fuse related?


The PO gave me his diagnostics report from December 2013:

1. His mechanic confirmed it starts hard (manual says to prime before turning key)

2. tested Fuel pressure - at spec of 80 psi at rest is 45 psi overnight dropped to 37 psi - all w/i spec

3. Coolant sensor, micro switches and Eha valve all at spec.

4. Test powers and main starting voltage is ZERO at Eha Valve. Test load reduction relay and is open circuit. Bypass and engine runs and starts normally.

5. Req a load reduction relay due to corrosion. Veh has new battery possible during boost it blew the corroded fuse in the relay. (he replaced Over Voltage Protection Relay)

6. Inspect state of tune, spark plugs new but wires don't hold on tips of plugs (I changed wires early August 2014).

7. Dist Cap is oil soaked and plug wells have oil in them, rotor is pitted, causing misfire, requires cap rotor wires and proper set up

8. Numerous oil leaks visible from top. Valve cover, timing chain covers, recommend shampoo and dye test for leaks (I changed valve cover and shampooed engine early August 2014 - no oil or other stains on ground under car after 3 days driving).

9. Says heater issues may be related to possible stereo installer knocking off a vac hose or power wire. Check Control Heads by removal of centre console (August 20, 2014 had med temp heat on low only - had a radiator co poke and prod + mechanic - said it could be air pockets &/or gummed up, flaps function fine. Suddenly came on full at all levels and had to turn it down it was blowing so hot, need to check floor flow)

So that's the history that I'm aware of - would any of this affect the dash meters?

TIA.

There is the problem with running and fuel...

For the gauges I would replace ALL fuses with the correct ceramic fuses.

[Holmesuser01]

I know we're talking about a 300. I've got a 190E, and I had issues with the cold start valve. It made the thing hard to start first thing in the day.

There's a check valve on the fuel pump.

How old is your OVP? If you don't know, might replace it. I did, and my computer system came back to life in a day of driving.

Check ALL vacuum lines for leaks.

Check the fuse for your gauges first. Old fuses can corrode. I replaced all fuses on my car when I got it, and have never had an issue.

I have never had to pump the pedal to start my car. You shouldn't have to either.

[OrangeGuy]

Slow off the line because it starts in second gear! Probably exacerbated by the tuneup issues.