How difficult to install IP on '82 300 TD Wagon - PeachParts Mercedes-Benz Forum

bassmun · #1 11-16-2009, 12:49 PM

So I need to replace the IP on my '82 300 TD. Is it hard to do, or just time consuming? Is it something that someone with average mechanical ability should be able to do?

Also, should I just put on a used one, or spring for a $700 rebuilt one?

junqueyardjim · #2 11-16-2009, 01:07 PM

How do you know you need a new IP. It is very rare for them to wear out.

bassmun · #3 11-16-2009, 01:37 PM

Quote:

Originally Posted by junqueyardjim

How do you know you need a new IP. It is very rare for them to wear out.

Well, the mechanic I took it to said that he thought it was pretty much dead. Basically I have been losing the prime on this car and having a really tough time getting it back. The clear plastic fuel hose running from the back of the IP to the main filter has been showing air bubbles. I can pump the priming pump and the air bubbles don't seem to go away, so there is obviously an air leak somewhere.

I have replaced all the rubber fuel lines in the engine bay, but have not replaced the rubber lines that connect the diesel tank to the main fuel lines. Someone mentioned to me that I could try replacing the o-rings on the IP under the fuel valves. I don't know where to get them though. Any suggestions on where ti find them?

junqueyardjim · #4 11-16-2009, 01:41 PM

Sounds to me like you have to work harder to find the air leak. Replace the IP and I'll bet your problem is still there.

bassmun · #5 11-16-2009, 01:50 PM

Quote:

Originally Posted by junqueyardjim

Sounds to me like you have to work harder to find the air leak. Replace the IP and I'll bet your problem is still there.

Yeah, I think you might be right. Might as well exhaust all possible problems before replacing the IP.

holtonmusicman · #6 11-16-2009, 02:07 PM

Is the primer pump original? you might try that first as well, if that has a leak you could be introducing air everytime you try and prime it. As well as sucking in air with the IP (through the primer pump) during operation

bassmun · #7 11-16-2009, 02:10 PM

Quote:

Originally Posted by holtonmusicman

Is the primer pump original? you might try that first as well, if that has a leak you could be introducing air everytime you try and prime it. As well as sucking in air with the IP (through the primer pump) during operation

I replaced the old priming pump earlier this summer. Perhaps the new pump is leaking, but I have not seen any puddles of fuel under the car or anything.

Graplr · #8 11-16-2009, 02:37 PM

Did you replace it with the old style white/clear or the new black? The old ones are notorius for leaking.

If you get stumped and we can't help you (I bet the forum helps you figure it out) I would take it to a different mechanic. Electrical IPs wear a lot more rapidly than our mechanical ones. Replace the IP is a common step most mechanics do...problem is on our cars, the IPs will most likley outlast the engine.

tobybul · #9 11-16-2009, 02:54 PM

Quote:

Originally Posted by bassmun

Well, the mechanic I took it to said that he thought it was pretty much dead. Basically I have been losing the prime on this car and having a really tough time getting it back. The clear plastic fuel hose running from the back of the IP to the main filter has been showing air bubbles. I can pump the priming pump and the air bubbles don't seem to go away, so there is obviously an air leak somewhere.

I have replaced all the rubber fuel lines in the engine bay, but have not replaced the rubber lines that connect the diesel tank to the main fuel lines. Someone mentioned to me that I could try replacing the o-rings on the IP under the fuel valves. I don't know where to get them though. Any suggestions on where ti find them?

You didnt really state the real symptom. Is it that the car won't start? Keep it simple. Trace back from the injectors to the fuel source. Any leak in the fuel supply line will introduce air. Some IPs will trap air and it has to be pumped xx number of times untill all air is out. FSM says if there is air in IP, pump it till your the relief buzzz. I didn't know what they meant at first when this happened to me. After pumping it over 30 times, I heard the IP buzzz. Its an indication that fuel has reached the relief.

If this does not work, continue tracing the line all the way back to the tank.

johninva · #10 11-16-2009, 06:51 PM

Recently I had an issue where after the car ran for about 15 minutes it would run really rough, stumble, cut off at idle and be hard to restart for until it cooled down. I replaced all lines, filters, clamps, primer pump. Finally swapped out fuel lift pump with a junkyard one and haven't had the problem since. Id try lift pump before ip if all else has been exhausted

Diesel911 · #11 11-16-2009, 09:04 PM

I agree with the rest if you are seeing Air Bubbles you have an Air Leak. You actuall diagnosed the problem yourself. (Why I never take anything to a Mechanic; the think they know what they are doing but don't.)

The reason you do not see Fuel leaks when you have an Air leak is because there is 14.7psi of atmospheric pressure at sea level pushing on the hoses and such all the time and Fuel is thicker than Air.

Combine the 14.7psi pushing in and the negative pressure inside when the Fuel Supply/Lift Pump is operating and you get an Air Leak through areas Fuel will not come out of.

You can change the 2 sections of Fuel Hose that hook to the Plastic Primary Filter for a few dollars with SAE 5/16 30R7 Fuel Hose that sells at any Auto Parts store. It is rated for Diesel Fuel as well as Gas.

Look under the Car at the Hoses that come out of the Fuel Tank and see if they look old and cracked. Also this is the place you might see the Hoses seeping as it is the lowes place in the Fuel System. Or you could simply drain you Fuel Tank and change the Hoses.

All the Hose changing is way cheaper and less complicated than the IP replacement you had in mind.

The Hand Primer is the next likely source of an air leak.

Diesel911 · #12 11-16-2009, 09:06 PM

Quote:

Originally Posted by johninva

Recently I had an issue where after the car ran for about 15 minutes it would run really rough, stumble, cut off at idle and be hard to restart for until it cooled down. I replaced all lines filters clamps. Finally swapped out fuel lift pump with a junkyard one and haven't had the problem since. Id try lift pump before ip if all else has been exhausted

Yes, that is the only part that can create the suction/negative pressure to for the Air Leak to take advantage of.