B230FT Stuck under 3000 rpm

[TheLoganZilla]

My first post on this site; greatly appreciated the information I've managed to find here, but I just can't seem to get a solid read on this particular problem I'm having. Currently, I am on a road trip in my 1993 Volvo 940 Turbo. A day or two ago I was accelerating on the highway when all of a sudden I got a large backfire and the engine started lurching. I let down on the throttle and it went back to normal. Ever since then, the engine has absolutely refused to break 3000-3100 rpm. If I give it half throttle and build boost, it's happy up 'til 3000, then I get pops and lurches; if I roll into in gently at highway speed, the engine just stops climbing at 3000. There are no other changes to how it runs; starts the same, idles the same (a little lumpy but never stalls), and drives the same below 3000 rpm. If I have the car in park it'll rev happily up to redline, but not when it's under load. I checked the codes and its throwing a 3-1-1 code indicating the speedometer, but the speedo works fine when I'm driving. Could that code be a cause or an effect of the problems I'm having? I also checked the airbox and intake piping up to the turbo for obstructions but found none. Any thoughts are greatly appreciated as I would rather not blow up my motor in the middle of a trip.

Mods include:
3" decat turbo-back exhaust
td04hl-19t turbo (13c crapped itself after 200000 miles)
IPD lowering springs
Bilstein shocks all 4 corners
Poly front bushings
Oil Catch can installed to assist with oil in the intake

[Toupe454]

Might be a big boost leak. My 740 Turbo did similar things when I left the charge pipe between the intake manifold and intercooler disconnected on accident. The first backfire might have even been a pipe or coupler giving out.

[linuxman51]

you gotta wideband? what's the AFR's.

usually popping and lurching is lean. where ya at right now?

[2 old for this]

Have a competet assistant power brake it, stand on the brakes and open the throttle while you check for boost leaks under the hood. DO NOT STAND IN FRONT OF THE CAR.

[TheLoganZilla]

I have an AFR gauge in my possession and have the sensor installed, I just haven’t had an opportunity to install and wire up the gauge as I’ve been on the road. That’ll be the first thing I do when I get settle somewhere for a few days. Only reason I don’t think it’s a boost leak is because I have a boost gauge and it’s holding vacuum no problem and doesn’t seem to be having any trouble building the boost up until the car stops revving.

On an interesting note, today, the car acted slightly different from the other days. Without me changing anything that I can tell, it will now make it up until about 4000 rpm if I go gently. It will still miss if I stomp on it, but for some reason it’s decided to go up to 4000 otherwise. I’m going to thoroughly inspect the piping tomorrow in the daylight for breaks, and I’ll recheck the codes as well. I think that the car is running rich too, as my tail pipe is quite sooty and there’s a decent amount of white smoke coming out of the exhaust. My gas mileage has dropped slightly as well. That AFR needs to go in pronto. It seems that this may be a compound issue, or at least a very large one. I just hope it isn’t spelling the end of the car as I have big plans for it.

[TheLoganZilla]

I do not currently have an assistant I can use to check for leaks that way unfortunately. I won’t be somewhere I can get real help for another couple weeks. I have to make it Wyoming first.

[2 old for this]

Look at all the inter cooler hoses. You might find one split.

[ZVOLV]

You probably have a torn hose somewhere. Common places are at the turbo inlet, IC outlet coupler (remove the hose and check), and the idle air hoses.


OR the common soggy turbo inlet hose sucking shut.

[TheLoganZilla]

I just replaced all of the hoses in the whole bay, so hopefully, it isn't a split. I'll take them off to check though. I'll also put a couple of hose clamps around the inlet hose to try and keep it from collapsing. I will report back with findings soon.

[ZVOLV]

I have had issues with loose hose clamps being tough to find.


You could spray around with various substances and see if the idle changes.


You say there was "loud boom" and NOW runs poorly.......... probably a hose ruptured or came loose

[TheLoganZilla]

A couple new developments. The problem has gotten worse, unfortunately; now the car will effectively not accelerate at all. If I give it more than a quarter throttle the engine bogs and starts to stall. I was barely able to limp it to Alabama. However, on the positive, it threw a new code that gives me a new direction to go in. I got a 2-2-1 code, indicating a very lean mixture while at partial throttle. This would explain the way it was acting and gives me some new ideas. I will continue to go over every hose I can get my hands on to make sure there are no leaks or bad connections. But this also indicates that some part of the fuel sending/pressure system is faulty, or the AMM is no good. Does anyone have suggestions for testing some of the parts in question: fuel pump, fpr, AMM? I’m basically stuck in Birmingham until I can get this fixed, so any help is greatly appreciated.

[TheLoganZilla]

Also, on a side note, I don’t think that the sound I heard was a hose rupturing. One, I just replaced all the hoses save for the IAC hoses in the whole bay, tiny vacuum hoses included. And two, the sound came from the rear of the car, and I could replicate it by pressing down on the accelerator quickly; I believe that the noise was actually a backfire coming from the exhaust caused by the lean condition.

[bobxyz]

Try a power balance test. At idle, disconnect one injector at a time and see if all the cyls behave about the same. You may need to give it some gas if it's not running well.

If one cylinder makes little or no difference, check the injector and plug wiring carefully for that cyl. Have you used a compression tester before (if not, ask or google)? If you have one, or can borrow one, a compression test would help diagnose the problem.

Another simple test, on a cool engine, would be to disconnect the air filter to turbo intake hose and, using your fingers, see if the compressor wheel spins freely and can't be shoved over enough to cause binding.

[TheLoganZilla]

I did a compression test right after I got the car. Each cylinder was hovering right around 150 psi. And while I was putting hose clamps round the turbo inlet pipe I also checked the compressor turbine for play. It has just a little bit of radial play, but it’s not a ball bearing turbo so that’s unsurprising. I plan on taking sons time to unplug a bunch of stuff on the car while it’s running to try and coax out a broken part. I’d also like to do a fuel pressure test, but I don’t have a gauge on me. I’ve heard that these cars require more specialized fuel pressure gauges to test?

[linuxman51]

Originally Posted by TheLoganZilla

A couple new developments. The problem has gotten worse, unfortunately; now the car will effectively not accelerate at all. If I give it more than a quarter throttle the engine bogs and starts to stall. I was barely able to limp it to Alabama. However, on the positive, it threw a new code that gives me a new direction to go in. I got a 2-2-1 code, indicating a very lean mixture while at partial throttle. This would explain the way it was acting and gives me some new ideas. I will continue to go over every hose I can get my hands on to make sure there are no leaks or bad connections. But this also indicates that some part of the fuel sending/pressure system is faulty, or the AMM is no good. Does anyone have suggestions for testing some of the parts in question: fuel pump, fpr, AMM? I’m basically stuck in Birmingham until I can get this fixed, so any help is greatly appreciated.

if you can get it about 80 miles south we can do the full run up on it and probably sort it all out in an afternoon, I'm down in montgomery but I can't really escape during the week

[JohnMc]

Possibly a plugged muffler (if you have one)? I've had exhaust issues on two cars (145E had a muffler collapse internally and block 95% of the flow, and a cracked coil pack melted the cat on my old Jetta GLX with a similar level of blockage) - both acted fairly similarly. With a weird inexplicable 'rev-limiter'.

[TheLoganZilla]

Ok, new development. Got in contact with a gentleman near me willing to help me out on short notice. Did a fuel pressure test, and not to my surprise, it read quite low on idle. While the fpr was plugged in, it was at about 25 psi while idling, then when unplugged it shot to 35. Tried squeezing the fuel line exiting the fpr and the fuel pressure started to spike, so I thought it was the regulator. I replaced it with another 3 bar regulator from inter motor (I know it isnÂ’t super high quality but I donÂ’t have the luxury of waiting for a nice unit to arrive). At first it seemed to do nothing, however, on the second time I started the car up it cleared up and drove like it had originally: not perfect but I could build boost and rev out to redline while accelerating. So I thought I had it. However, just tonight, on the second drive IÂ’ve taken it on since it cleared up, itÂ’s back to backfiring and being stuck under 3000-3500 rpm again with the backfires under heavier acceleration. I still think itÂ’s fuel system related and I plan to do another pressure test when The gauge I ordered arrives at my next stop, but I wanted to document this and ask for any more advice you guys have. Are there any other parts in the fuel system I should replace besides the pumps? Is there any possibility now that you have this new information that it isnÂ’t fuel related? Should I pony up for a leak down gauge or a compression tester?

[ZVOLV]

I would pressure test the induction system. I use an expensive smoke machine. The new one we have is thousands of $$$. Cheap ones are hundreds of dollars.

On the cheap, maybe rig a vacuum cleaner on reverse and BLOW into the intake and listen/feel around for leaks. Others here have had luck with a cap from Home Depot clamped into the intake hose at the MAF and adding some shop air to pressure test.

At 0 inches vacuum/boost the fuel pressure is what is listed on the FPR. Under a vacuum, the pressure is LESS. Under boost, the pressure is HIGHER than listed on the FPR. I think you may be looking in the wrong direction re: fuel pressure.

Failure to rev is usually really retarded ignition timing, or really lean mixture.

Does it rev freely in Neutral/Park?


It could also be a dead MAF, but I doubt it based on the symptoms. You could put a meter on the signal OUT of maf and rev the engine and see what happens. But that is a rather inconclusive test.

Based on experience, you have an air leak. Have you sprayed around with brake cleaner/propane/hairspray/starting fluid and see if the idle changes or stalls.

[linuxman51]

fuel pressure without vacuum applied to the regulator should be around 44psi (3 bar).

how bout this, can you get video of the car acting up?

have you disconnected the battery cables and allowed the lh to clear it's trims? (pull the positive off, touch it to negative, let it sit for a minute or two)

[h20ham]

I like this smoke machine, $10
https://m.youtube.com/watch?v=tixozqgSwN0
Have you tested resistance in your relays, yes. Non working relays still click. The important thing in a relay, like a circuit breaker in a house. There can be arcing. Once you get enough carbon deposits, the resistance goes up to the point of no current.
Can’t recall, if you’ve tested your fuel pressure regulator, or put in new plugs.

[TheLoganZilla]

Only reason I suspect the fueling is because of that statement you made in your post ZVOLV; the fuel pressure should be 3 bar when the fpr is unplugged. When I tested it before replacement, it was not, it only made it to about 2.4-2.5 bar, or 35 psi. I should be able to recheck that tomorrow as well to see if it has improved. I also don’t think that it is an air leak, though I will try to find a way to pressurize the system to check. My vacuum levels while idling are normal, about 20 mmhg after warming up in park, this is exactly the same as before I started having the problem. Secondly, like I mentioned, it is a strangely intermittent and fluctuating problem. It seems that every time I start the car just about, the car acts one of three ways: it has no power whatsoever, has power in the low end up to 3400 ish and then goes no higher, or it behaves about normally with maybe a small misfire here or there around 3500. I can also see that I am not losing boost when the car is in that third possible state. I’m going to try to get a video tomorrow of the car driving with me attempting to accelerate so that you guys can see exactly what is happening. Also, yes, the car does rev normally while in park, not sure about neutral though. I am also going to check my plugs and the fuel pump relay. Would it be worth taking off the timing cover to see if the belt has skipped?

[spock345]

I encountered this problem when I tried to run NA injectors on a +T to limp the car to another storage place. So I am going to wager it is a problem with the system not delivering enough fuel.

[dl242gt]

Follow the symptom. Your fuel pressure is low. The fuel pump is bad or maybe it's a clogged fuel filter. If you do replace the pump. Put a new filter on as well. Be very careful with the short hose that goes from the pump to the filter.

[mhgreen]

I had some wacky weird symptoms kinda like this in an '85 BMW that turned out to be the fuel filter .

[TheLoganZilla]

Well, after much finagling with the wiring under there (the connector style had been changed from oem) I was able to get the pump on, working, with no leaks; I had replaced the filter a couple days ago. The last person to replace the pump clearly used some cheap aftermarket brand, it didn’t even have a part number, so it crapped out. This seems to have solved many of my problems too, more than just the rpm limit. It idles better, less smoke out of the exhaust, and drives much smoother. Glad to have this one figured out; time to move on to the next problem out of an endless list, I can always find things to improve. Thank you everyone for your comments; hopefully this thread helps someone else in the future.