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Weekly Fuel injection puzzler #2

1K views 15 replies 11 participants last post by  NAIRB 
#1 ·
lol, bosses car is acting up again. She swears that I "fixed it" last night, but I don't think I did.

So the problem with it is that it had like zero power. Again, I just drove it to see how it felt. It basically accelerated like you had your foot a 1/4 inch on the throttle no matter how hard you pushed the peddal? I rapped it up a couple of times, didn't smell rich or anything. It accelerated very smoothly, just didn't recognize the amount of throttle you had. If you floored it, it would slowly accelerate, hold its shift like its supposed to, but give no throttle. Keep in mind, it started very easily, ran smoothly and well. If I had to guess, I would say the AF ratio was right on the money, computer driven of course.

SO I figure it must be a sensor of some sort. I got under the hood and felt around the throttle linkage to see if maybe a trigger was being held up by the throttle body. I rapped it a couple of times and we went inside to our company function. She said when she drove home the car was all better?

So what's the deal? Throttle position sensor gone bad or something? If that's the case, the trans uses a separate unit (like a kickdown cable) right?

Am I right on the money on this one, or off?

1994 volvo turbo inline 5 cyl.

K
 
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#5 ·
Killer,I do not know on that car,but a TPS should store some sort of fault code.What type of ignition is her car?If it has individual coil packs for each cylinder,one or more may be dropping after they are warmed up. She drove it home after it cooled down and it seemed to be ok. A coil pack will not throw a code. Find out what the resistence is and when it gets to acting funny check the coils.Hope that helps you some man.
 
#7 ·
Typically TPS is used for acceleration enrichment only. An alphaN type setup trys to run the engine off of TPS alone, but I dont think any oems used anything like this. It just does not work well. My bet would be in the fuel filter. Seems like if that was the case, however, when you punched it the car would stumble and backfire.

Chris
 
#9 ·
My boss had a Volvo with the same problem. It ran perfectly but acceleration crawled. It turned out to be the ecm. Just like a rev limiter can prohibit your car from going over a certain speed while runing perfectly fine, so can the ecm fail and produce the same effects at lower than normal speeds. Got one at a junk yard for 150 dollars and it ran fine ever since. Rick BTW Loved your troll kill. lol
 
#10 ·
lol, thanks!

Yeah its not the fuel filter or ignition. I said it ran really smoothly, its obviously the computer thinking its at a lower throttle. If it were a mechanical problem or a fuel problem we'd have misfires, however we have none of that. Thanks for the help, I'm pretty sure its a TPS.

K
 
#11 ·
You are not understanding the TPS sensor role in the system. The ECU changes fuel pulse based on the MAP,IAT, and engine speed. The MAP sensor reflects what is happening with the throttle position. ECU in turn changes timing based on similiar parameters and the engine revs up. TPS has few other functions, but the main one is for the ECU to produce a "accelerator pump" shot when the throttle position changes rapidly. Typically this is a time/distance ratio.

Before you go changing anything, I would get the codes read. If it is the TPS, it should show up. If there are no codes, I would not be surprised if it was the ECU. It almost sounds to me like it is running in "limp home" mode. Sounds silly, but this is usually a backup set of parameters so if something goes really wrong you can "limp home".

Chris
 
#12 ·
It's the engine gremlin. These little critters live in engines during the cold weather to stay out of the elements. They get bored and do random things to the motor for entertainment. When you rapped on the engine it understood the warning that you considering taking apart his winter environment and cut it out for awhile.





That's my story and I'm sticking to it. :)
 
#13 ·
Before you go changing anything, I would get the codes read. If it is the TPS, it should show up. If there are no codes, I would not be surprised if it was the ECU. It almost sounds to me like it is running in "limp home" mode. Sounds silly, but this is usually a backup set of parameters so if something goes really wrong you can "limp home".

Chris [/B][/QUOTE] Isn't that what i just said, just not so techically?:mwink:
 
#14 ·
Oh, I'm not going to be doing the work more than likely. I'm just trying to think of things to help out a little bit. There's got to be an electronic cause to this, maybe MAF if its not the TPS. Its also odd that its such a smooth running problem, lol. I immagine that the motor knows how much air its getting, because it doesn't backfire or anything. Its also odd that when I messed with the thottle body it went away. THis car, as I mentioned, is turbo equipped, I wonder if it has much to do with that? The boost gauge wasn't building much, but at 1/4 throttle as the motor "thought" it was at, I wouldn't immage it would-

K
 
#16 ·
If there are no trouble codes, I woud check the basics first, which would be fuel pressure and with loss of power, be certain that the catalytic converter is not stopped up.

These are the two things I would check first, particularly if the car idles well, but has no power.

Brian
 
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