'98 S70 Jerky hesitation Topic is solved

Post by **dosbricks** » 10 Apr 2017, 18:09

Once again seeking advice from the wise and experienced. '98 S70 na 229k
Symptoms: Momentary rough idle on cold start. An occasional quick hesitation (sort of a jerk) especially when easing off the gas--could happen at 40mph or 70mph or anywhere in between. Seems to pull OK on acceleration.

What I've done: Changed plug wires, cap and rotor--all OE. No change. Plugs have about 10k on them and look OK.
Next I jumpered pins 15 & 87 in the fuel relay connector. The car started and ran great on a 5 mile test run. So I replaced the relay with a KAE OE equivalent from IPD. But the car continues to have the same problems.

This is the on-demand fuel system without a return line, so the pressure regulator is not up front on the fuel rail. It just has a pulse damper up there.

So I'm thinking fuel pump going out or possibly a bad coil. Or possibly the new fuel relay is defective? The pump runs continuously with the jumper wire replacing the relay, so this seems to point to a fuel problem. The fuel pump and coil are original to the car. Would appreciate any suggestions as to how to proceed.

Thanks, ~ dos

Post by **theWIFES_S70** » 11 Apr 2017, 00:24

Hey dos, 229k on the original pump?? I hope you picked up that OE Bosch fuel pump on clearance over at Rockauto last night... I'd plan to swap that out soon. But before you do that, you try cleaning out your throttle plate? The key aspect of your symptoms that really stands out is how it all smooths out when you accelerate.

You replace your throttle cable?

Post by **dosbricks** » 11 Apr 2017, 07:50

Yes, I cleaned the throttle body first thing (cheapest). I'm going to order the pump motor today, because it's going to need it soon, if not already. Thanks for the tip. Is Rockauto trusted for selling genuine Bosch and not Chinese knock-off in Bosch box?

The throttle cable snaps back fine. I've had it loose and dry lubed it.

This S70 has the red relay 3.302.230. I have a spare pink 103 relay from my 850. From what I can tell from the parts catalogs of IPD and FCP, they are interchangeable. Do you guys think it would be OK to try that 103 in the S70 to see if it would cure the problem the way the jumper wire did?

Post by **misha** » 11 Apr 2017, 11:25

If the car runs fine with a jumper wire in place of fuel pump relay and problem re-appear with new KAE fuel pump relay...that indicates that fuel pump relay is bad.
KAE????
Put a Bosch,Hella or OEM one in there.

Post by **theWIFES_S70** » 11 Apr 2017, 12:39

I have to agree with misha here. The KAE relay is only good as a stopgap. If you don't want to go OEM, get a used one off eBay.

I'd take a knock off Bosch fuel pump insert over most fuel pump inserts out there... I haven't had any reason not to trust rockauto. I know their $5 suspension parts aren't meant to last anywhere close to what OEM parts are supposed to last...

Post by **dosbricks** » 11 Apr 2017, 19:36

OK guys, thanks for the input. I'm headed to Pull-A-Part tomorrow to try to harvest the relay from a '99 S70. If that works good, I'll order an OE from FCP and keep that one for a spare.

By the way, the KAE (made in Germany) was the only relay IPD sells for S70. I'll be returning it if this gets sorted out and will report back the results when it happens.

I ordered the pump insert from Rockauto today and new seal to have on hand when the need arises.

Post by **theWIFES_S70** » 11 Apr 2017, 20:10

dosbricks wrote: ↑11 Apr 2017, 19:36 I ordered the pump insert from Rockauto today and new seal to have on hand when the need arises.

I know, I'm wondering if I should do the same thing too...

I believe the last two digits on those fuel pump relays indicate when it was fabricated. So just get something made in 05 or newer and you won't need to order a new one.

Please post if this fixes the issue. I think more data on using KAE fuel pump relays is needed!

Post by **dosbricks** » 12 Apr 2017, 12:47

New development: I got the relay from a '99 S70 at the JY. To my surprise it was a red 103, but I figured it would work because that car also had the on-demand no return line fuel system. It did not work at all--car would repeatedly die immediately after started.

So I'll go with the advice given and order an OE from FCP.

Post by **misha** » 12 Apr 2017, 18:52

It have a return line...it's just in fuel filter area where also a fuel pressure regulator is and damper is at fuel rail.
Older cars and M4.3 have fuel pressure regulator at fuel rail where also a return line is.

Post by **theWIFES_S70** » 12 Apr 2017, 19:01

misha wrote: ↑12 Apr 2017, 18:52 It have a return line...it's just in fuel filter area where also a fuel pressure regulator is and damper is at fuel rail.
Older cars and M4.3 have fuel pressure regulator at fuel rail where also a return line is.

Misha, I've always been curious, what exactly does the fuel damper do? Is it something we should all start replacing as we approach year 20 on our cars?