Volvo S70 '99 Cruise control surging / pulsating, headache!

Post by **precopster** » 13 Jun 2018, 05:08

When represented with Vida it's more like 16-18 degrees at idle. Don't know why this is the case: have a look at throttle angles in ECM and you can have a live report of each. At the same time note the variance between sensor 1 and 2

Can you perform the ETM test in Vida ?? (only if you have 2006 plus software in your ETM)

Post by **abscate** » 13 Jun 2018, 05:14

I’m guessing mike is right on this, my AUTEL scanner is reporting some other parameter.

Pater · Post by **Pater** » 13 Jun 2018, 07:42

Klausc wrote: ↑11 Jun 2018, 18:31 The idle speed should not fluctuate. Check your intake manifold vacuum as you might have a very small leak. 80-90Km/h is almost idle speed in top gear.

This idle fluctuation is very small, ±25 rpm. I've done all the vacuum leak checking and I found a small crack in a hose in the EVAP system close to the fuel filter. This did improve the idle fluctuation by approx. 10rpm, but such small vacuum leaks would not be able to interupt the engine on higher loads. As expected it did not change my problem @ 80-90 km/u.

Pater · Post by **Pater** » 13 Jun 2018, 07:54

j-dawg wrote: ↑11 Jun 2018, 23:34 I noticed recently that mine handles moderate grades at about 65mph very poorly. It seems incapable of generating a moderate amount of boost on hills - it goes straight from 0 to 4 psi or so. Then I tried it with my own foot and realized that I myself could barely moderate the throttle to keep the car at exactly the speed I wanted it on that hill. It strained my calf to keep the car climbing that exact grade at that exact speed.

Next time you notice it fluttering, cut off the cruise control and try to maintain your desired speed with your foot. You might find the same thing I was running into: at a certain engine load, around a certain throttle setpoint, the throttle mapping is extremely sensitive, and the cruise control's inputs don't have sufficient damping to handle it gracefully.

So on my car at least, it's not just speed, but speed and throttle setpoint that cause this issue. A thing you could try: next time you're going uphill or downhill, try going at the speed that gives you trouble. If it now can hold the speed, you have brought yourself out of the combination of engine speed and engine load that gave you trouble by changing only the amount of torque you were asking the engine for. If the throttle is sensitive around 3000rpm and 20% throttle on flat ground, maybe it's fine at 3000rpm and 40% when you're going uphill.

Now how to fix that issue, I couldn't tell ya. In the five years I've had the car, I've only run into that combination of speed limit and incline once. Sounds like your trouble combo is more regular for you.

Thanks for your feedback! I was thinking in a similar way. I did notice that the cruise control stops pulsating when a higher load is needed (climbing). After reaching the top of the climb and getting back on a flat road it starts pulsating again. Therefore I do think this might be indeed a throttle sensitivity problem during certain engine load (flat road, 80-90 km/u).
But if this would be a sensitivity issue, all the same configured vehicles should suffer from this issue. I'm not sure if this is the case, as I dont have a second S70 '99 available for testing.

On the other hand, I'm perfectly able to hold manually a stable speed at 80-90 km/u without surging and a very small throttle position fluctuation (<1%).

The question remains is, what parameter is the ECM using while turning the cruise control on and is less important when driving without cruise control engaged?

Could be still an over-sensitive ECM while it has to calculate the throttle position (cruise) instead of just listening to the throttle pedal...

Pater · Post by **Pater** » 13 Jun 2018, 07:57

scot850 wrote: ↑12 Jun 2018, 07:35 Maybe it is around the speed top gear locks up at. I think that is around 90kph or slightly higher. If that is the case then maybe the engine is working hard to maintain speed in that condition?

Neil.

It has a manual gearbox. The surging is also not related to the selected gear or rpm, as it also surges in 4th gear at the same speed.
Speedsignal is stable on CAN...

Pater · Post by **Pater** » 13 Jun 2018, 08:04

precopster wrote: ↑13 Jun 2018, 05:08 When represented with Vida it's more like 16-18 degrees at idle. Don't know why this is the case: have a look at throttle angles in ECM and you can have a live report of each. At the same time note the variance between sensor 1 and 2

Can you perform the ETM test in Vida ?? (only if you have 2006 plus software in your ETM)

I have a brand new OEM ETM installed with newest software, so should be able to execute the sweep test. Before I purchased this new ETM, I was using a modded ETM with magnetic sensors, xemodex style. This car behaviour on cruise @ 80-90 km/u was exactly the same, also slightly surging.

Personally I'm not confinced that the ETM is the trouble maker. From my read-outs during surging on cruise I noticed that the surging is forced by the ECM (desired throttle value). The ETM is acting on this incomming signal from the ECM.

Pater · Post by **Pater** » 13 Jun 2018, 08:06

abscate wrote: ↑12 Jun 2018, 08:04 My T5 throttle sits at about 8-9% when started, after warmup 5-6%

There is little fluctuation, small movements over seconds. Ill post a picture of the time trace here

Volvo IDle ETM Percent June 2018 - 24.jpg

Thanks for measuring idle behaviour. This is very similar to my vehicle (RPM & throttle position wise). Therefore the idle behaviour seems to be just fine on my car.

Pater · Post by **Pater** » 13 Jun 2018, 08:15

The following questions are remaining:

- What parameter is the ECM using during cruise control and is less important while driving with manual throttle?

- Manual throttle is working perfectly, the surging is only there when the ECM has to calculate it's throttle position instead of following the accelerator pedal.

- Is there any information available about how the Denso ECM calculates the desired throttle position while cruise control has been engaged?

- Is there anyone else on this forum experiencing the same problem with a '99-'00 S70 20V with Denso ECM?

Post by **precopster** » 14 Jun 2018, 04:49

I have a 99 Denso ECM here that I didn't use from an auto V70. The key chip (Eprom) can be soldered in from your own ECM and use it as a tester. I can identify the Eprom and mark it for you. Yours for the cost of freight to NL plus a small fee

Was yours the 4 speed auto and no VVT on cams? Have you removed ECM and cleaned contacts?

By the way cruise control is added to the DIM (not ECM) on 99-00 P80s You can swap in another DIM from a car with cruise from parts salvage.

The ECM does the calculation based on speed sensors on the transmission. Is OBD II reporting speed accurately as well as the speedo? It may pay to remove transmission connectors and clean all contacts with CRC or similar

Pater · Post by **Pater** » 23 Jul 2018, 11:01

precopster wrote: ↑14 Jun 2018, 04:49 I have a 99 Denso ECM here that I didn't use from an auto V70. The key chip (Eprom) can be soldered in from your own ECM and use it as a tester. I can identify the Eprom and mark it for you. Yours for the cost of freight to NL plus a small fee

Was yours the 4 speed auto and no VVT on cams? Have you removed ECM and cleaned contacts?

By the way cruise control is added to the DIM (not ECM) on 99-00 P80s You can swap in another DIM from a car with cruise from parts salvage.

The ECM does the calculation based on speed sensors on the transmission. Is OBD II reporting speed accurately as well as the speedo? It may pay to remove transmission connectors and clean all contacts with CRC or similar

Just put another 5000km's on the odo during my holiday. Still got the light surge on cruise on lower speeds, but this is not noticeable @ 120-130 km/u.

I've got a manual gearbox (M56) and no VVT. I did remove the ECM and cleaned the contacts. I've also inspected and cleaned the ECM ground on the chasis (and all other grounds).

As it is a manual gearbox, I do not have the aditional VSS? From my knowledge the vehicle's speed signal is determined by the 4 ABS sensors.

VIDA says the cruise control is integrated in the ECM for the 1999-2000 models, this does not add up with your information?

What I did discover is that the speed signal, from the ABS module, goes to the CDM (instruments cluster) first! After that it's transmitted to the CAN network, says VIDA.
The weird thing is that you can read the 'Vehicle speed CAN signal' from the ABS module directly (within VIDA). Maybe this is the signal that gets transfered to the CDM before its forwarded to the network?

Speed signal is stable on both OBDII and speedo. Altough, the digital speed signal (CAN) might be a high frequency signal which can not be analyzed by one of these that quick?

I also noticed that my car is not equiped with the latest CDM software as upgrade '30677009' is available for my car. Does anyone know what this upgrade does?

Volvo S70 '99 Cruise control surging / pulsating, headache!

Re: Volvo S70 '99 Cruise control surging / pulsating, headache!