Hi All

Strange problem on my 1990 740GL Non turbo, Rex Regina. Car runs fine when cool. Once engine temp comes up, car bogs down, does not cut out, just loses almost all power. If you keep pushing it, it will pop occssionally out of the exhaust. Idles normal. No trouble codes. Plugs look normal.

I tested a couple sensors today. Air temp sensor OK, Man pres. sensor Ok. I was thinking maybe a clogged converter but I don't believe that would come on instantly and then have the problem disappear. Seems to go away when the air temp is lower or when the engine is below op temp.

What about the knock sensor? Any of you have that cause symptoms like this? I un plugged it this am when the problem occured and the car ran better, not normal, but better. Will be checking ignition timing tommorrow once I have my tools. Will also hook a vacuum gauge to it to test for plugged exhaust.

Anything else?

Thanks
Barry

Connected a vacuum gauge...really low vacuum. Checked timing marks, off about ten degrees. Looks like the belt skipped two or three teeth. R&R cylinder head while I'm in there.

One thing I would try because it doesn't cost anything and it's a known problem area on the Regina systems....

Take the coil apart (seperate it from the power stage) and clean the internal connections and all the mating surfaces. Also clean the mounting surface to assure a good chassis ground.

Okay, did a much needed overhaul to the cylinder head. Since this car was leaking oil and anti freeze at the head I replaced head gasket, timing belt and all other related gaskets (basically from the block up) cap, rotor, wires, fi temp sensor (since it was buried undr the manifold), distributor oil seal, valve adj, new cushions on vales (boy did that quiet things down). VAcumn hoses, claened flame trap, crankcase breather box. Coil cleaning and test as Chris Mullet mentioned complete. All grounds related to Cyl head and manifold were cleaned. Other sensors as mentioned prev. tested.

Once head gasket was replaced I drove for a couple hours and everything seemed fine. Today, same problem is back...intermittent no power at all RPM's except idle. Does it cold or hot. Never stalls, just won't get out of it's own way! Car looses power like someone is turning a switch off and then normal power comes back. Does not do this long enough to test any components while it's acting up. No check engine light.

Anyone...ideas?

blocked exhaust ?

All exhaust is new except converter. Seems weird that this would cause such an intermitent problem. Drove about 40 miles to work and back home (each way). It only acted up about 3-5 of those miles on the way home and was normal the rest. Ugh, I hate trying to take all that apart (gravel driveway/rusted bolts) but it may be worth a look at this point, I am at a loss since it won't malfuntion long enough to perform normal tests. i.e. it's never broke when I try to fix it!

I would check fuel pressure.

Found a little bit of sludge in the MAP sensor vacumn tube last night. Three little bubbles of crankcase residue found there way in from the intake. One of the few things I did not clean! Not a total blockage but it kinda bubbled when trying to force air through it. I suppose it could cause false MAP readings to the computer. Cleaned this with carb cleaner, let it dry. Car started and "seemed" to idle a little smoother/start easier and idle faster cold. Did not test drive but maybe this is my intermittent bog.

Fuel pressure...Had a questionable vacumn line on the regulator. I replaced it to be sure. Unfortunately I damaged fuel line trying to attach pressure gauge. Thought I could cut the line and tee into it with some barbed fittings on my gauge...don't try this! Line is plastic under the rubber cover and barbed fittings do not re-seal. Now I need to replace the line all the way back to the fuel filter. Once I repair this and get a good pressure reading, I'll test drive and post results.

That's a high pressure line. When you check the pressure, check to see if it holds the pressure. It must hold the pressure after you turn the key off. If not the check valve is bad on the fuel pump.

Got a pressure gauge hooked up but had some leaks and ran out of time to screw with it more. Powered the pump by turning the key off/on several times. Pressure read around 42 by the time I got to view the gauge. But with all the leaking fuel I abandoned the test so I prolly lost some pressure from the leaking. Still not able to do a running check to see if the reg was holding a steady 36.5 at idle. However When I pulled vacuum on the reg it dropped to around 36 quickly. Once I can run these tests I'll install a new fuel line from a junker. BTW fuel pump is about five years old. Installed it myself when I got the car.

Too bad Volvo did not make this a little easier to do on an otherwise well engineered auto. This is one of the few areas where I have been frustrated with their design. Diagnostics should not be so difficult to perform without spending $$$$$$$$ on a "special" tool or racking your brain to make your own. Even with the special tool FAQ it's difficult/expensive. Spare lines and fuel rails don't come cheap where I am located!

So, fuel pressure gauge issue sorted out. All within spec. 45 psi with vac line unhooked & plugged 36psi with vac attached. Went for drive, started bogging down again. Opened hood after struggling to get up hill to home and noticed exhaust manifold glowing red. Will remove exhaust next to see if there is a blockage. I suspect the converter since everything else was replaced less than two years ago. Will post results but it may be awhile. I leave for vacation this weekend and not sure how much time I'll have mess with it.

Exhaust off, cat is melted and debris in rest of system but not clogged anywhere. So, I am pretty sure it's running rich when bogging. Still no check engine light.

Sensors that I have tested, MAP sensor (I suspect this one the most), Sensor in intake hose (name escapes me) and the coolant temp sensor for the FI under the intake manifold is new. I replaced that one when I did the cyl head gasket because it is so hard to get to.

Now that I am sure the exhaust is not clogged I can put it all back on and see if it still bogs. I am sure it will since I did not find any obstructions.

I am at a loss since everything seems to test okay but only malfuntions periodically when driving. Wish I knew someone who had a Regina car to swap a few sensors with locally. Any ideas would be appreciated...

Even though this references a turbo, sounds like your problem.

http://www.brickboard.com/FAQ/700-900/EngineTurbo.htm#TurboHasPowerLossandCherryManifoldKnockSensor
--
Post Back. That's whats makes this forum work.

Lol, you beat me to it. I was just posting this when I read yours. Won't hurt to re-post:

"
Turbo Has Power Loss and Cherry Manifold: Knock Sensor. [Inquiry:] My 740t intermittently looses power and the exhaust manifold turns bright red. I don't know if the two are related but when the car was in the loss power mode I opened the hood one night to check for arcing wires and I noticed the manifold glowing.

[Response: Abe Crombie] Those are the symptoms of a knock sensor problem. The knock sensor may be bad but more likely the connector is the problem. When the ignition control unit detects no input from sensor the timing is retarded which is the safety from excessive spark knock but this does make engine power suffer and the delayed timing sends exhaust gas temp skyward.
" Brickboard FAQ

Also, would a bad fuel pressure check valve cause anything other than hard starting?


Good Luck,
Will
--
1990 740 Turbo, on its way to stock specs, maybe beyond

Wouldn't that throw a trouble code though? At the beginning I suspected the knock sensor but moved on to other items i could test easily with my DVM.

I also suspected the MAP sensor. I accidentally knocked the vac hose off of it on a timing belt change a few years ago. It runs exactly like it did that day when it's bogging down. But the MAP passed tests okay. I just found out today my other GM make car has the same MAP sensor. I am going to swap them tonight and see what happens there. I still need to put the exhaust back on which I dread doing...90 degrees, 75 percent humidity, working in a gravel driveway.

I may be able to "borrow" a knock sensor from a co-worker to test. I hope it's not a wiring issue but from what Ive seen in the electricals in these machines it's very possible. I'll keep you posted. Thanks for the HELP!

Rather than put the exhaust back on and drive, I decided to try a couple more tests. I connected a vacuum gauge and started the car and warmed it up. At idle, it read a little low and fluctuated. Indicating a retarded timing. At around 2500RPM it would read fine at times and then read a little low (same flucuation as at idle). I swapped the map sensor with a known good one...no change.

My timing light is on the fritz so I need to borrow one to verify the timing is really retarding. But in the mean time, other than the knock sensor, what else could cause the fluctuations? Again, this comes and goes, idling and driving now. When it first started it only appeared to affect the engine while driving (loss of power, burnt out converter, glowing exhaust manifold). Just wanna cover all my bases before I plunk down another $50!

Replaced knock sensor. Manifold still glows red. On and off power when cold...nothing when warm. Low vacuum off and on when idling, really low vaccum when reved. Obviously I've missed somethng.

Relaced:
ECT Sensor, Knock Sensor, Wires, Cap, Rotor, Plugs, Air Filter, Oil, Oil Filter

Other stuff Done:
New Head Gasket, Intake gasket, exhaust gaskets, Vacuum hoses(all checked but double checking tomorrow) Valves lapped in (looked good).

Checked:
Map Sensor, Air Temp Sensor, Exhaust (not Clogged but converter was MELTED)

I have not checked compression since reassembly. Perhaps that is the next step. I am at a loss. I have done everytthing I can think of and tried every suggestion form those who have replied and the FAQ.

Wife comes home soon. She'll want to scrap it and buy a Toyota!

HELP!

Frick'n O/2 sensor...unhooked it. All vacuum readings returned to normal as did all other operations. Idles smooth as glass (I am sure it's running a tad rich in this mode). Check engine light on of course. Will drive a couple days with it unhooked to see if problem repeats or not.

Why the hell are the no test values about Regina o2 sensors anywhere? (read: not blaming us on the BB, just NGK and the internet in general). At least a cold value and hot (warmed up) value would be nice so you could test the range and see if you are close.

Thanks for all who helped guess at this. You helped eliminate things that were not broken so I could narrow this down! I'll repost if this is the REAL fix or not. When and if I get a new sensor, post some readings and temps to help others.

Go Bricks!
Barry

"Why the hell are the no test values about Regina o2 sensors anywhere?"

Hi Barry,
Google on "Titania O2 sensor" for a lot of interesting background but little solid tech info. For that you need Volvo "Green Book" TP 31903/1 for "Fuel system Regina and Ignition system Rex". Mine was $29.15 about 7 years ago.

For O2 output checking it has no cold spec (does Bosch?) but says to start the engine and put meter between the signal line ("one pole connector") and ground.
Meter should vary between 0.1V and 1.2V. Then it gives some possibilities depending on an abnormal out put.

It also shows a drawing of an OK sine wave for those values, with equal flat-topped peaks and valleys.

"Frick'n O/2 sensor..."
There's been no history here (6+ years for me) of ANY Regina O2 problems. If yours is bad, I'd wonder if it's cause of (or due to) to the glowing manifold and cooked cat mentioned earlier.
--
Bruce Young, '93 940-NA (current), 240s (one V8), 140s, 122s, since '63.

Barry..Im glad a fix is on the way..Let us know for sure..now just be sure to get the right sensor and post..I too have a regina system

The o2 sensor did not fix this POS. Made it worse than ever. YAY just what I wanted! What a money pit! If the o2 sensor is unhooked car runs well. Not so great on gas mileage.

Offers? I have about $500 in this "problem" so far. Tired of the effort and energy that it takes to own and maintain this car. A mechainically sound machine hooked to a wasteland of electrical gremlins...an incredible shame.

I've dealt with Alfa Romeos and Fiats with notorious electrical issues. I never thought I would see worse. An amazing feat of elecrtical engineering.

reads at ZERO (TDC). No advance at any speed...0-5000 RPM no advance ever shown What would cause no advance at all on a rex regina system?

I am off all day tomorrow to check wiring. Any ideas where to look first? All sensors have been replaced checked etc double checked. Next step is to trace every wire. I suspect the problem is in one of the factory connectors creating high resistance and sending false info to the computer.