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740 four-cyclinder turbo cranks easily but has no power while warming up. Smells rich at tail pipe and feels like timing off, but when gets a little warm, smooths out and has power. Gets worse the colder it gets, but when temp gauge moves about a quarter up, runs OK. Temp sensor is fresh, no codes showing from computer. Please give me some ideas, have another 740 turbo, so can swap parts to fix, thanks
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Hello, Check for leaks in the supply side after mass airflow sensor, check with propane your intake gasket for leaks. Pauli
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Out '90 744TI had its thermostat jammed open by the PO (or someone else). It could not have gotten in the condition it was in by itself, it was pulled open, then twisted to jam it. It never warmed up properly until I put a new thermostat in.
I then found out that the electric fan was siezed - hence the thermostat trick.
This car also had a hole in one of the turbo hoses and the idle control was doctored as well to make the mixture quite rich.
I bought the car in July and had cold weather starting problems when winter came.
After those items were fixed, we never had problems starting it.
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'96 855R,'64 PV544 driver, '67 P1800 basket case, '95 855, '95 854, the first three are mine, heh, heh, 415,000 miles put on 9 bricks
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The rearmost of the two temp sensors; under the intake for cyl #3? And is this one a non-turbo?
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Andy in St. Paul - '91 745 218K mi, '91 745 210K, '90 744 189K, all Rex-Regina - past 240s
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Andy, I will change the temp sensor (rear below cyl. #3) again, as I have plenty of spares, but just changed it a month ago when computer code said the old one was bad. Is this sensor the main warm up sensing device, or should I look somewhere else also, thanks
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I just wanted to make sure you were replacing the sensor for the computer, not the one forward of it which is just for the dash guage (never heard a good reason for there to be two). Aleekat's reminder to use the correct sensor for your model is a good one two as others fit, but don't work right.
You also have a cold start injector which should only open when starting when it is VERY cold out; like below zero F. If that were opening for too long, it might give your symptom. You could unplug it to test, or even pinch off the fuel line to it to eliminate the possibility that it is leaking all the time. But be warned that I once split one of those lines pinching it off.
Also, check your fuel pressure regulator for fuel in the vacuum line. If the diaphrams leak internally, that can route gas back into the intake manifold. I had a Regina car that wouldn't start when it was below freezing out and replacing the regulator cured it.
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Andy in St. Paul - '91 745 227K mi, '91 745 210K, '90 744 194K, all Rex-Regina; '86 745 GLE M46 230K; past 240s
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Hope you had a good Christmas. Have been plugging away and changed temp sensor (was black) just in case, made no difference. Fuel regulator has pressure and no gas smell, but am looking for another just to test. Seemed to have problem with bad idle hunting during all this so I changed the Idle air valve, and put in a cleaned one, and idles lower and doesn't hunt.
Still has low power when warming up but actually seems like getting better, or maybe just not as cold lately. Even swappped out computer from another turbo car and seemed to make no difference. Will do some more tests when stops raining, and thanks for the encouragement.
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Make sure the sensor your putting in is the "black" one. The blue is for 89 and below. I would also really check over all your turbo hoses, turbos really hate any type of air leak. Look for softness, cracking, etc. AMM to turbo hose is know to crack, on the underside.
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Post Back. That's whats makes this forum work.
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Thanks and of the five Vovlo's I have had, never realized the difference in the temp sensor color--I guess that's what makes these cars interesting--or a big headache. Swapped out for another black one but seemed to make no difference, and testing other ideas---please keep throwing them at me. All hoses are tight and good. This warm up problem feels like the timing gets retarded, no power. I keep searching the manuals and wonder if there is something with the Thermotime switch in the radiator that is retarding the timing at warm up.
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