Big hesitation on small or constant throttle
 

Hi All, recently bought an 1800E. As I drive it I often get a huge hesitation enough to jerk your head forward. (can't think of a more technical term). It's as if the engine momentarily cuts out. applying a little more throttle, or lifting off immediately sorts the problem. I've never had the sense that the car is going to conk out. Otherwise, the car starts and goes well. I've recently changed the distributor to a 1,2,3, electronic one, which made absolutely no difference (although the car does run sweeter). So I suspect a fuel problem (?). Doesn't feel like electrical, as the hesitation is stopped by moving the throttle pedal. Blocked injector?

Any suggestions from all you wise people very gratefully received.

Maybe dirty contacts in the throttle position switch - TPS. Gently clean the tracks with a rubber pencil eraser.

Hi,

I agree with Derek, likely cause is a dirty or broken contact in the throttle position switch.

Can be cleaned with gentle rubbing with a pencil eraser and electrical cleaner on the circuit board. They are difficult to source if a replacement is needed, but Scandcar in NL show them on their website:

https://classic-volvo.com/140-142-14...xchange-f.html

There was also once a seller from NL on ebay who had replacement circuit boards available but I couldn't find him when I just looked.

Hope this helps, Paul.

Superb! Um, where is the throttle position switch, please?!

sl;

Follow Throttle Cable to Throttle...on the other side of cast housing, and also on the Throttle Shaft, is located the TPS (black plastic enclosure). I'd start with unplugging TPS to see if symptoms persist...gentle acceleration ONLY then, as no accel enrichment pulses are called for or produced...then I'd move on to cleaning /lubing TPS (I caution about using anything abrasive on the gold plated "comb contact" of TPS... (the angstroms thick only!) gold plating you wear off today will make it sooner tomorrow that PCB is worn down to (corrosive) copper, and will need to be replaced. I recommend cleaning/flushing with Deoxit D5 and a cotton swab only...DO NOT ADJUST OR BEND any internal contacts of the TPS, but follow procedure I have published at link.

If you consider replacing PBS, you must first determine which version is necessary, early or late...easily determined by radial or radial plus angular "comb contact" geometry. See link.

If you have to ask where TPS is, I have to take it that you are on the steep part of your learning curve...in that case, I recommend you study the very good general D-Jet troubleshooting booklet: http://volvo1800pictures.com/documen...lt_tracing.pdf

Before point the finger at sensors, one of the first things that must be assured with the D-Jet system is fuel supply, supply rail pressure, as well as Injector spray pattern.

Ref: http://www.sw-em.com/bosch_d-jetroni...nformation_tps

Good Hunting!

Ok, I was aware from the manual that there are no user-serviceable parts in the fuel injection system! But thank you very much for the detailed advice. I will follow it precisely!

The guy in the Netherlands servicing these is Ton Telgenhof, here's his details.
I highly recommend his full refurbishment service, unit comes back looking and working like new.
David

Thanks David, I was beginning to doubt my memory but you've confirmed that there is in fact a Dutchman who can provide a lifeline to D Jet owners!

Paul

Jerking
 

Had same with my ES. New not refurbished gas tank and both filters appear to be the cure so far.

Thanks once again for these really helpful posts. Will keep you informed of my progress (though a just-discovered weeping brake hose has now to take precedence 🤐