'94 940 turbo-idles well-can't hold steady RPM's

Zdadgeezer · Post by **Zdadgeezer** » 02 Jul 2012, 13:50

I would appreciate any feedback. Unfortunately I guess my search capabilities are flawed and I can not find specific reference to what I am looking for.
My issue- during recent emissions testing I discovered that the car will not maintain a smooth constant RPM. Background of the car- 101k original miles, recently replaced Ignition module( past 6 months). Timing belt/ tensioner replaced within past year and a half this is the third belt .Radiator same time as last timing belt cracked top hose connector. Plugs,Wires, rotor and cap replaced two years ago.
My son( new driver) had complained of something being not right to this effect some time ago but I never got around to verifying.
Replaced top hose (radiator) 2 weeks ago didn't like the autozone or whichever I had bought last year(too short) and bought the OEM at FCP Groton/Euro.
Several weeks ago I was researching the OBD codes trying to see if I could help get an answer for someone seeking help here in the forum. My car was not throwing any codes at that time(1-1-1).
Now and for the life of me I do not know why it is throwing 2-3-1 although I do not believe it is related to the RPM issue as I stated previously my son had complained about it and I had looked at codes and none were present.
I checked the MAF and it appears normal does the post run burn-off etc...
I believe the ignition module should be OK as it is relatively new( although new does not mean good I realize).
I replaced vacuum lines when I did the radiator hose to the fuel reg and turbo as well as several manifold lines which I do not know their purpose but needed replacement(cracking/dry rot) and a few connective unions as well to carbon cartridge.My vacuum holds steady at 107mmHg.(Good?/ Bad?) Throughout RPM range.
After reading and looking for info here I am suspicious of the fuel pressure and I remember in doing diagnostic checks for research a few weeks ago I noticed I could not hear one of the fuel pump checks. I attributed this to my lack of experience testing or my hearing. I did discover the A/C was not functioning and tore apart the MCC and repaired some broken solder joints however. Which I found the info here. Sorry off topic.no codes generated for that though.(Took incomplete photos of process) but proud of result.
I have seen in some of the threads that 43.5 psi is one of the values for the pressure but I have also seen 70 psi as a reference. I hear a pump on key turn momentarily. I would assume this to be the primary?
When the car runs it may or may not hesitate initially upon accelerating and it makes speed but it just runs erratically from idle up. When idling it does not appear to drop or sputter as it does when accelerating or trying to maintain a steady RPM.
I was going to start with the fuel filter but I would like to know a good method of testing fuel pressure without setting oneself on fire and what to expect as a standard.
Or if I am going in the right direction at all.
The 2-3-1 code is driving me bonkers the last time it was present was before the ignition module replacement but I also had the CEL which does not come on now.
Thanks in advance for your help.

Post by **jimmy57** » 02 Jul 2012, 14:48

Inspect your hoses from turbo to intercooler, intercooler to throttle for leaks. Intercooler could have a crack or end tank leak also.

2 3 1 is for fuel trim too rich or too lean at part load so injection ECU knows it isn't an idle issue. When turbo makes pressure it can blow open a split hose or cracked intercooler and then the air that has been measured by MAF is getting that level of fuel injected but that air for combustion has leaked out.
Have noticed if the car has black smoke from tailpipe if driven away at moderate throttle?

Zdadgeezer · Post by **Zdadgeezer** » 02 Jul 2012, 19:17

The car has always run "Rich" and yes I get a nice black cloud when accelerating, this has been the nature of the car for 18 years and I just stopped trying to resolve, because plugs , wires etc... never changed anything and did not generate codes. I will definitely inspect the plumbing.

Thanks

lummert · Post by **lummert** » 02 Jul 2012, 19:43

In 18 years was the engine temp sensor ever replaced?

Zdadgeezer · Post by **Zdadgeezer** » 02 Jul 2012, 20:23

lummert wrote:In 18 years was the engine temp sensor ever replaced?

Yes actually about 3 or 4 years ago maybe less, it was one of the first things I did a while back when I had a different issue with cold start rough idle problems. There is one thing that has bugged me though and I have attached some photos. The bump on the intake manifold somehow from the inside? That has been there since I bought the car. The car was dealer serviced until the magic number for everything serviced on the car went over $1500 per visit so that stopped about 15 years ago. I have managed pretty well since then but as we both age the issues become more complex? I forget what I had for breakfast and the car forgets it's supposed to get me there.
I digress.
I will answer Jimmy57 here

Inspect your hoses from turbo to intercooler, intercooler to throttle for leaks. Intercooler could have a crack or end tank leak also.

I did and could find nothing amiss. Although the intercooler is presenting a bit of a challenge to me to be completely thorough and positive. The plumbing is solid and tight.
Thanks

Post by **jimmy57** » 02 Jul 2012, 20:29

The crack from the inside out is a new one on me. No residue of oil so it isn't leaking.

Volvo1man · Post by **Volvo1man** » 03 Jul 2012, 14:49

I may have missed it in the earlier posts, but have you checked or replaced the RPM sensor? It is located at the rear of the engine, on the bell housing if I remember correctly. I had a terrible time with my 1994 940 Turbo not running right until my mechanic ran his hand down the sensor wire from the top of the engine compartment to the bottom. He found that the last 4-5 inches were completely stripped of insulation and shorting out one another. I had him replace it with a Volvo part it was all under $200. The car runs better than it has in a long time and the strange occasional electrical gremlins have gone away. Maybe it is something dimilar with your car?

Zdadgeezer · Post by **Zdadgeezer** » 03 Jul 2012, 22:25

[quote="Volvo1man"] but have you checked or replaced the RPM sensor? It is located at the rear of the engine, on the bell housing. quote]
If this is the guy(feeble red arrow) then it is in fine shape. It is the only cable I found going into the bell housing at the rear of the compartment. Also it passed the proper codes in Diagnostic 2 for testing the sensor 1-4-1.
Thanks
I'll try the simple things first like the fuel filter. Will post with results.

Zdadgeezer · Post by **Zdadgeezer** » 03 Jul 2012, 22:29

jimmy57 wrote:The crack from the inside out is a new one on me. No residue of oil so it isn't leaking.

I love being unique.
Thanks

Zdadgeezer · Post by **Zdadgeezer** » 05 Jul 2012, 21:31

I'll try the simple things first like the fuel filter

Simple my ass. What a nightmare, what should have taken a half hour took two.I recommend dropping the assembly if you have never replaced the filter before because the fittings were quite a challenge. Also a small container as it drained about 3/4 to a quart of fuel. I PB'd the hell out of them and still munged up one side slightly damaging the tubing. (photo attached of damage and repair). I will need to replace the high pressure pump because it is not working(recommendations welcomed). I used a Purolator filter F64857 $27.99 at Pep Boys, I know the FCP price on the Bosch was $17 and change but I wanted to try and fix before the weekend. I will order a pump and short fitting as well as vacuum fuel regulator because nothing really changed. It runs slightly better(15 to 18 yr old fuel filter) but still is erratic above idle. If nothing else I hope it is a good tutorial on filter/ fuel pump replacement.
The Swedes love sagas and this one continues.