Author Topic: How do ya like these numbers? (Read 3962 times)

dieselweasel · « **on:** April 17, 2005, 08:39:39 pm »

In an attempt to track down the cause of poor fuel mileage on my Golf (~30-35 mpg us), I pulled out the injectors today and did a compression test. Cylinders 1 and 3 had 440 psi while 2 and 4 compressed 480 psi. These numbers are well within spec, since the wear limit is 377 psi and the max difference is 70 something.

I'm taking the injectors to get them tested tomorrow, and rebuilt if necessary. Will post updates.

farkman · « **Reply #1 on:** April 18, 2005, 04:45:16 am »

Oh yeah, how do you like these numbers!

I filled up today at 1010.3km with 52.671 litres at Sunoco. With the 2% oversized winter tires I have on, that comes to 46 mpg

.

chrissev · « **Reply #2 on:** April 18, 2005, 05:42:29 am »

Quote from: "farkman"

Oh yeah, how do you like these numbers!

I filled up today at 1010.3km with 52.671 litres at Sunoco. With the 2% oversized winter tires I have on, that comes to 46 mpg .

680 km for 32.95 litres = 48.56mpg on an 88TD with leaking return lines. If I could get the diesel to stop running out of the lines and down the front of the block, I could easily get her up over 55mpg. Oh, and that's mixed highway and city driving, and I drive with a heavy foot and spool my turbo up habitually.

chrissev · « **Reply #3 on:** April 18, 2005, 05:51:27 am »

Quote from: "dieselweasel"

In an attempt to track down the cause of poor fuel mileage on my Golf (~30-35 mpg us), I pulled out the injectors today and did a compression test. Cylinders 1 and 3 had 440 psi while 2 and 4 compressed 480 psi. These numbers are well within spec, since the wear limit is 377 psi and the max difference is 70 something.

I'm taking the injectors to get them tested tomorrow, and rebuilt if necessary. Will post updates.

re: your poor mileage: could be lots of things: look for dragging brakes, uninflated tires, low fluid in transmission, clogged air filter, bad thermostat that isn't letting the engine warm up, stuck or broken cold start mechanism, pump timing too advanced. That's all I can think of now. There's probably more.

racer_x · « **Reply #4 on:** April 18, 2005, 09:41:24 am »

Check everything Chrissev mentioned. A stuck open thermostat is especially easy to overlook and will hurt fuel economy quite a bit.

dieselweasel · « **Reply #5 on:** April 18, 2005, 11:41:24 am »

Well, I got the injectors tested. The nop is a bit low but still within spec. The spray pattern is not perfect but decent. The fellow at the injection shop didn't figure the injectors were the cause of my problem. Given the cost of rebuilding injectors, I went with his advice. He suggested I advance the pump timing some more, which is now set at the Bentley spec of .0315". He was saying that he times those pumps to .038" but the Bentley says it shouldn't be more than .034". Either his information or the Bentley's is incorrect. I'm going to go time it now to about .034". He also suggested that there could be a problem with the pump, but I'm not going to spend the money on a rebuild.

Chrissev, I've checked all that you've mentioned and more. Thanks for the suggestions.

farkman · « **Reply #6 on:** April 18, 2005, 12:42:00 pm »

Dieselweasel

The information the guy gave you about pump timing isn't incorrect and neither is the Bentley manual. The Bentley manual uses the numbers given to them by Volkswagen. This setting is okay but if you time the pump ahead a little more (to what that guy said) the engine will most likely run better (more power and better fuel economy). Quite a few members have timed their pumps more than spec with no problems.

What is your driving like? Lots of city or highway?

Crissev

Those are some pretty good numbers. Was that in summer or winter? This tank was on winter diesel and winter tires and about 80% highway/20% city. I'm hoping to get 48mpg in the summer.

chrissev · « **Reply #7 on:** April 18, 2005, 01:01:16 pm »

Quote

Crissev

Those are some pretty good numbers. Was that in summer or winter? This tank was on winter diesel and winter tires and about 80% highway/20% city. I'm hoping to get 48mpg in the summer.

Those numbers are from the last two weeks (I monitor the mpg constantly). In the winter I was getting 640km to the same amount of fuel, but this includes about 3 minutes of warm up plus lots of cold running before reaching normal op temp, the winter numbers are always low. In summer I can hit 700km for the amount of fuel specified, but right now as I mentioned, I have a problem with leaking return lines. In summer I can get over 50mpg if I confine myself to long distance highway driving at sustained speed of 110-120km/hr. This is a 1.6TD jetta though. A 1.9TD will be less fuel efficient because it's bigger and makes more hp. My little 79 rabbit diesel with the NA 1.5 litre used to get close to 60mpg on a regular basis, and this was back when diesel could be bought for 47 cents per litre. I once drove it to Thunder bay for $30. Those were the days.....

Chris

dieselweasel · « **Reply #8 on:** April 18, 2005, 03:06:32 pm »

Thanks for your input farkman. I timed the pump to .0335" today. I'll see if that improves the fuel economy any then maybe bump it up some more. Just don't want to go so far that cylinder pressures go through the roof and I start cracking pistons. At work we sometimes see the old mechanical Cats with timing too far advanced and it cracks the aluminum pistons.

My driving is mostly highway, prolly around 75%, and I rarely go over 110 km/h.

Since you're bragging about your fuel economy, I'll brag that I got excellent fuel economy once. Driving back from Halifax, I filled up in Calais, Maine, then went 980 kms and filled back up just before the bridge to Canada in NY. I got 44 mpg. I attribute that mileage to the fact that I was going 80 or under the whole way, and only shut the engine off once for an hour so it didn't cool down. Lots of mountains though.