Alfa Romeo Forums banner

41 - 60 of 88 Posts

·
Registered
Joined
·
4,307 Posts
Well actually this tweaking with a resistor is only for aesthetic purposes because you are not going to get an entirely accurate result regardless. Even if you were to use a calibrated mechanical gauge and a variation of resistors to adjust it you're only going to be able to dial it in at a specific point such as at cruise rpm. As I pointed out, what would be the purpose of knowing exactly what pressure you had at any given moment? The oil pressure gauges in automobiles are generally just glorified idiot lights anyway. You would never use one and record it's readings to do any sort of troubleshooting or make any kinds of adjustments. The only reason these Sunpro units are used is because, as I pointed out, it's difficult to accept the visuals of a tachometer needle at 5000 rpm and an oil pressure indicator needle on zero, even though the low pressure light is not on and you know you have pressure. I don't know if anyone has even assessed the accuracy of the original sender prior to failure either so there's really no basis for the adjustment to begin with other than where you feel you want to see the needle pointing.
 

·
Registered
Joined
·
5,646 Posts
Paul -- its the same ole story-----

Measure it with a micrometer
Mark it with a piece of chalk
Cut it with an axe!
 
  • Like
Reactions: blu105

·
Registered
Joined
·
9,977 Posts
Discussion Starter #43 (Edited)
I checked the accuracy of the SunPro/Bosch sender w/22 ohm resistor against a mechanical gauge and it came out within 2-3 psi. I'd rate that pretty darn accurate for an automobile gauge. If you can have that accuracy for a 50 cent 22 ohm resistor, why not?

In the research for this, I measured the actual ohm value that the gauge needed for a specific reading, then matched the modified SunPro sender to it, all cross referenced and validated by a mechanical gauge.
 

·
Premium Member
Joined
·
16,073 Posts
I'm using the Sunpro with the resister in both 164s as, being supposedly educated an engineer, it's kinda in my blood to have things read relatively accurately. I just like it like that even if in real life, it's not terribly important for the reading to be that close, as long as we know the deviations.

I do watch the gauge to get a feel of the changes due to what I've been doing with the car. As well, that also is not particularly important unless there are significant changes, but I do notice resultant effects at times, depending on a number of changing factors. I don't anal about it.

I do remember my 64 Sprint GT, which had the 'in dash' oil temperature gauge. Now that was interesting, to see the temperature changes, depending on what I had been doing with the car, relative to the matching oil pressure.
 

·
Registered
Joined
·
5,646 Posts
I'll bet anyone here a beer that the variability of sunpro senders at midrange is more than 22 ohms . Anyone want to play? I have 3 or 4 new in box senders that I could instrument if I was motivated enough...
 

·
Premium Member
Joined
·
16,073 Posts
Could be, but the two in my cars read the same at the same hot rpms. I did check both with a mechanical gauge, same readings, +/- 2-3 psi. Probably coincidence, tho.
 

·
Registered
Joined
·
5,646 Posts
Del yeah but john corrects 2 to 3 psi with the resistor! Plus how can we tell 2 to 3 psi on that dash gauge?

The AFM on each and every 164 24v car are individually laser trimmed for resistance vs wiper travel. Like the AFM, but unlike the temp sender, mechanical linkages are integral to the sender. Personally I think it's fun to trim this stuff up but part of engineering is error budgeting and I have to admit I too get excited to 'calibrate' stuff -- but we should be careful about thinking that our calibrations with 22 ohm ( by the way, is that a 1% metal film, or a 5,10, or 20% tolerance resistor/ is it temp corrected?) are really legitimate?

Anywho it's fun to fix stuff !!! Always great to make a gauge read more accurately!
 

·
Premium Member
Joined
·
16,073 Posts
That's why most people are entirely happy with just a red light, no gauge. And few evidently pay attention to the light, judging by how many cars are driven home after the light comes on. Anyone with offspring drivers?
 

·
Registered
Joined
·
4,307 Posts
Well for what it's worth I actually have the 22 ohm resistors (Now as to where I put them, that's a different story) and I admire John for figuring all that out. I can completely understand the drive to do that. As I'm finishing up the A/C work on Blackie in the next few weeks maybe I'll install one - if I can find them :whistling:
 

·
Registered
Joined
·
9,977 Posts
Discussion Starter #50
If you look at the data I gathered, the 2-3 psi delta is at normal operating engine speed. It does vary slightly more than that at low and higher RPMs. I just thought it best to make the gauge most accurate at normal running RPMs.
 

·
Premium Member
Joined
·
16,073 Posts
I think it was the correct thing to do, as that rpm range, ~2900-3200 rpm is where most of the life of the engine is spent.
 

·
Registered
Joined
·
5,646 Posts
For Me bottom line

Nice work by John to characterize
I hate seeing 0 psi at idle on the gauge even though I KNOW it's no zero
I wouldn't want it pegged full scale all the time either!!
So use sunpro, adjust with resistor if you want!!

My personality is a lot engineer like in that the doggone temp sender just bugs me seeing it at 230F. Just like OP at neAr zero. Just don't like it-- maybe I'm an idiot light guy at heart!!
 

·
Premium Member
Joined
·
4,761 Posts
Interesting discussion. I have a factory setup on RC. Well almost. I have a SunPro in replacement of the factory sender and it feeds the dash. No resistor as I am only interested in "am I making pressure and does it go up and down when revving?". For giggles, I added an AutoMeter gauge to the car. Tapped into the low oil pressure port down the side of the engine. I'd say both read about the same tho the A/M unit reads "faster". They both show near zero at idle but the light doesn't come on. Stone cold startup is 60 psi. Running warm, the engine makes about 15 psi per 1000 rpm. Anyway, I just live with it. The thing that makes me crazy is the air in the line for the A/M unit tho the company assures me it is OK. Bleeding helps for maybe 3 hot/cold cycles. I'll sleeve the line this weekend and this issue will go away. There's a wee bit more than 50K on the engine.

The 164 and it's differing engine has a factory stock setup to include a new factory sender. At temp and speed(s) it shows 4 bar. Idle about 2. Close enough for me. I get where you guys are coming from tho. Ciao, chris
 

·
Premium Member
Joined
·
27,158 Posts
As ML tells me all the time. "Don't let [trying to be] perfect get in the way of doing good".
 

·
Registered
Joined
·
4,307 Posts
If I had "perfect" organizational skills I'd know just exactly where I put that darn pack of 22 ohm resistors :whistling:
 

·
Registered
Joined
·
2,231 Posts
Oh, don't worry, I enjoy the Q4 alot but I'm a bit of a purist in some things and such big offset bothers me a bit. Oil pressure is good, no doubt about that and that is wat counts in the first place, not?! ;)
I can identify with you and wouldn't mess with resistors if the oem part is available. Perhaps you should consider the Intermotor sensor you bought a loss—perhaps it is defective or the wrong part no.—and just order a new one.
Here are two easy sources, the first one specifically includes the Q4, but both give all the Alfa interchange numbers:

Öldruckgeber Alfa Romeo 155 164 TS 8V V6 TD Öldrucksensor NEU | eBay

Sensor, Öldruck FAE 14500 | eBay
 

·
Registered
Joined
·
35 Posts
I can identify with you and wouldn't mess with resistors if the oem part is available. Perhaps you should consider the Intermotor sensor you bought a loss—perhaps it is defective or the wrong part no.—and just order a new one.
Well, I couldn't help it and I disassembled the ****pit and opened it up. The little display with the milage was barely readable so I guess I could solve that; the flatcable on the display side needed a heat treatment (thermally connected to the graphite lanes in the glass) and it's readable again! :)

Now, about the oil pressure sensor, there is a big 2W resistor right beside the contacts where the oil gauge meets the printboard and it's a Purple/Blue/Blue/Gold/Brown 76,6ohm 1% resistor (but it measures 86 ohm). I just had to know so I changed this to a 33ohm one to see if it has any effect on the gauge and it has: on pre-start the gauge reads 'zero', just like it should be, if I start the engine the gauge reads around 0.8bar with hot engine idling and the needle actually moves when I'm revving so it's responding as it should be; on 4000rpm it reads around 3.5bar. I want to see tomorrow what the readings are with a cold engine, it should be around 4 bar cold idling... we'll see...

I can always make it original again if it is necessary, it's not that difficult at all.

http://www.164td.nl/pics/Q4/****pit/****pit06.jpg



EDIT: I changed the resistor to 51 ohm, now the gauge is showing 0.2bar at pre-start but I found a cold start did 3.5 bar instead of around 4 bar. Maybe I'll try a 56ohm resistor also just to see how the gauge will respond.
 

·
Registered
Joined
·
545 Posts
Well, after doing the "Del mod" of drilling a hole in the top of my oil pressure sending unit a few years ago, it's been leaking oil, so I did the second "Del mod," and put a sheet metal screw in the hole I drilled.
The screw seemed to have stopped the leaking, but my oil pressure kept indicating lower and lower, and now reads zero, and I'm back to leaking oil out of the top of the sender.
So after not being able to find the thin 14mm wrench I used before, I found some really thin, cheap Chinese wrenches in a set with a 9/16" at a Dollar Store, bought the Bosch sender (FST 7577), and the Bosch Metric Adapter Kit (FST 7573) that includes an M10X1.0 to 1/8" NPT, and even some 10mm crush washers (Earl's Performance Plumbing) all from Jeggs, and got ready to do the job today, but it turns out I forgot you need to fashion an adapter for the different electrical connector on the Bosch sender compared to the original blade connector on the Alfa sender.
I must have missed that in the post, but nice to have all the parts before you start the project.
 

·
Premium Member
Joined
·
16,073 Posts
I didn't even bother with the adapter for the different threads, as the sender screws in nicely snug far enough, without damaging any threads, to not leak or come back out. I do have the adapters and if I have nothing else to do someday, maybe I'll do it right. If the LS runs correctly on 6 cyls tomorrow with the used power module I got in the mail from a good Alfa friend, maybe I'll do the adapter change as celebration. Of course, my Sunpro installations have been in both cars for 5 years now, so I guess they are not going anywhere.

My thin wrenches are genuine Craftsman from the early 60's, back when they were better made, stronger, and thinner I guess. They work fine for accessing the 164S sender.
 

·
Registered
Joined
·
352 Posts
So I've installed the Bosch Oil pressure sender to replace the stock one for the stock gauge, AND I've installed a resistor in line as per the first page. Warmed up at idle the pressure sits between the 2nd and 3rd lines (just above the first thick line which I guess is about 25psi?) At higher rpms it just touches 55, but basically most of the times it lives around the small line between the first thick line and 55. Seems a bit high at idle and a bit low at speed, or is that what I'm supposed to expect?

BTW I did not install the sealing washer, it did not seem to fit over the threads on the Bosch sender. It does not seem to be leaking so far. I snugged it down but didn't ratchet it down hard, and I did not use rtv or teflon tape.
 
41 - 60 of 88 Posts
Top