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What happens at 1300 rpms

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1300 rpms
2K views 24 replies 5 participants last post by  Ralf S. 
#1 ·
My old beast has always had a bit of a glitch around 1300rpm.. it just hesitates briefly depending on how quickly I'm accelerating and the weather and the engine temperature (the slower, the colder makes it worse).

It runs okay either side of 1300 rpm so logically the HT system, plugs, TDC, lambda sensor, fuel pump etc. etc. must be alright but something obviously isn't quite right.

The hesitation is always at 1300rpm.. so I think it must be doing something at that engine speed but it's not handling the transition smoothly.

What's the beast up to and what's the culprit?


Ralf S.
 
#3 ·
Codes? I dunno... but apart from this little glitch it runs alright and passed the MOT on emissions.

Idle speed is dead steady 800rpm too, which is why I don't know where to look. It would be nice to solve it.. it's just a bit annoying.

Ralf S.
 
#4 ·
Can you poll stored ECU error codes using the throttle pedal trick on yours? (ignition on, don't try to start, quickly pump throttle all the way to the floor 5 times. Engine trouble light should flash off then on, , then pause, then flash a sequence of 4 digits. 4 lots of 4 is no stored codes, anythig else is an error code. It goes flash flash flash flash pause etc)

If yes, see what it gives....if not...find some nice soul with an FL tester you can borrow :(

Mine used to pass emissions when the lambda heater was working, but it had this unpredictable flat spot. Always under the same conditions, just unpredictable when it would actually happen IYSWIM....obvious when I found the cracked fuse of course.....
 
#9 ·
Can you poll stored ECU error codes using the throttle pedal trick on yours? (ignition on, don't try to start, quickly pump throttle all the way to the floor 5 times. Engine trouble light should flash off then on, , then pause, then flash a sequence of 4 digits. 4 lots of 4 is no stored codes, anythig else is an error code. It goes flash flash flash flash pause etc)
I don't think my beast has got an engine trouble light. At least.. I've never seen one... :eek:

He's a 1994 v6.. There's no immobiliser and no code key either.. :thumbs:


Ralf S.
 
#12 ·
Ah, OK - no pedal-polling then I'm afraid....pity 'cos it can be handy.

Try checking the wiring and 12V feed to the lambda heater. I know I'm always bangin' on about that...but it does seem to crop up a lot. Check the usual culprits, relay, and the fuse and the terminals. Might be worth checking the cabling to the probe as well depending on how it's been replaced in the past.
 
#13 ·
Aye okay.

The lambda relay is the one on the right of the three (by the steering fluid reservoir) innit?

Is the lambda heater wires the white ones? I'll check the circuit there too (I have spliced a new lambda to the old connector block).

Ralf S.
 
#14 ·
Ralf,

Yes & yes (I think!). It's the 7.5A fuse and the relay next to it. Put it another way, the engine will still run if you pull the lambda heater relay. The others are fuel pump and ECU power....so results of pulling either of those should be obvious ;)

Check the splices on the heater wires in particular as it takes a good amp or two when it's cold.

The symptom mine had....low revs light throttle and I could provoke the warning light (and hesitation) more or less at will. If it was properly hot or more throttle used, it was OK. The probe needs the heater to maintain an output at lower revs/loads as the probe is so far away from the engine, so it cools down quickly.

Worth a look anyway.
 
#17 ·
Ralf, had another notion to add to the list should it not be lambda/heater related....AFM is another possible too...could be the track is getting worn at the bottom end. Might have to do the old 164 trick and shift the ceramic substrate a wee bit so the wiper runs on a fresh bit of track. Mine has a bit of a 'hole' at the bottom I think.

Easy enough to check for a smooth variation in resistance (well, no holes in it anyway!) with a multimeter.

TPS as well. This should be easy to test with a multimeter too.

HTH
 
#19 ·
Cheers dude.. I'll have to get myself a multi-meter with tiny little prongs by the sound of it (mine has huge crocodile clamps on it.. :D)

How do you test the fellas and what readings am I looking for?

I'm pretty certain that the AFM and the TPS are both the original 1994 factory-fitted parts, so could be a *bit* tired by now.. :(


Ralf S.
 
#20 ·
I'd have to double check...but from memory, the TPS is a plain 4k7 (might be 5k) pot, so measure between pins 1 & 2..it should start around zero then smoothly increase to around 4k7 or so as you rotate the shaft. AFM is the same more or less, can't recall the pin numbers off the top of my head, and the other issue is that the track is made up of discrete resistive elements that are trimmed for accuracy, so IIRC, the resistance change isn't perfectly smooth - it steps slightly as you go upward, but the key thing is that it doesn't suddenly jump very high then back down again indicating a worn track. Can't recall if the AFM 'law' is linear or not....suspect it might not be, so don't be surprised if the relationship between movement and resistance isn't 1:1 - it may well give little change for a lot of movement towards fully open. Like I say, can't remember as it's a long time since I played with one of these things.
 
#23 ·
Aye! That all makes sense... if I understood any of it! :D

I was experimenting a bit and that little "jerk" is there between 1300-1500 rpm (the exact revs seems to be not 100% consistent) but it does not happen at higher revs, regardless of the throttle position, so I'd guess the TPS is okay.

Hopefully that narrows it down a bit.. but to where..? :confused:

Ralf S.
 
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