byrdman454

I have a '84 Euro that I finally am getting back on the road after the PO had a terrible shop screw everything up. It seems to start easy, run fine, except it has a lean condition. The car wants to "buck" in just about every gear about mid-throttle and if you floor it, it seems to struggle above 3500 rpm. It will keep climbing, but not like it should. I pulled the plugs today and they showed a very lean condition. The porcelean was very white with only a couple small brown spots. The car is stock. It has newly cleaned and tested injectors and a newly rebuilt LH computer. I have read some older posts and talked with DR about adding an adjustable fuel regulator, but I want to be sure it is not something wrong with the stock system first. Is there any adjustment to check? How can I check if I have adequate fuel pressure? What is that pressure supposed to be?

Thanks for the help.

FlyingDog

To be that lean with a close to stock car, something is wrong. My car had that bucking problem when the MAF connection was dirty, but mine was running extremely rich then. Are all the plugs in the same condition or are 4 bad and 4 okay? Are you sure the injectors are all getting constant 12V? Are they all firing?

To test fuel pressure you can either tap the rail cap or buy a replacement adapter from Tim Murphy. It goes on the end of the passenger side rail. Fuel pressure at idle should be ~30psi and should be ~36psi with no vacuum (part or open throttle).

PS. Nice taste in 928s! You need to update your sig line.

byrdman454

All the plugs are in the same condition, all white. When I was troubleshooting the bad LH, I did have 12V at the injectors. How can I tell if they are all firing. I would think there would be some sign on a particular cylinder if there was an injector problem instead of on all 8.

Thanks. Keep the comments coming.

k1woods

I'd check timing at the 3 pts, verify that the distributor belt is intact, Vacuum leaks, Grounds, MAF and a plugged exhaust. No particular order.

Also what work did the PO/shop perform?

Kevin
84 928 S2

FlyingDog

Since all of the spark plugs look the same and the engine runs, I would assume the injectors are all firing. To check if they're firing, you can pull the connector at the injector for each cylinder and see if it changes how the engine is running. It is safe to do while running. Just pull and plug each one.

MAF or fuel flow would be my guess, but vacuum or timing is possible. Plugged exhaust or broken dual distributer belt should make it run rich.

One thing to check on the fuel system is to pull the vacuum lines from the regulators (be sure to plug the lines to avoid vac leaks). That should make the car run rich at idle since it should be getting 36psi instead of 30psi.

John Speake

Is the car a stock Euro, or has it been Federalised with cat and O2 loop ?

If it is standard, and there are no inlet leaks, then I would think the MAF is the most likely problem.

The Euro is very sensitive to MAF ageing, much more so than the 87 and later cars.

byrdman454

The car was federalized. It currently has a '84 928 cat and O2 sensor. The importers spliced in a fuel control module to read the O2 sensor. I have since then had the LH rebuilt and this module removed. I was not sure it was even working anyway. So now the O2 sensor is just a plug.

Does anyone know what adjustments are messed with when a fuel control module is added? There is an adjustement screw on the MAF. Does anyone have the stock setting (how many turns out)? The POs inept shop may have messed with this also when they could not get it running.

What is the easiest way to check for inlet leaks? Is there a way to check the MAF?

Thanks

tv

John speake can correct me but i think it is a 20 turn with no stop so you will only know what the setting is by testing the maf. Use one of those ohm tester things on the LH plug in the passenger footwell. It should read between 0 - 1000 ohms. Around 500 or so being stock.

It is not uncommon for a euro to be lean. Cap the MAF and force air into the top there or into the y connector on the drivers side of the plenum and listen for leaks. Smoke would make it easier.

John Speake

Hi
tv has it right - 500ohm is a good starting point for the idle Co pot (assuming it is still in circuit)

If you remove the MAF, measure with an ohmeter between pin 6 and the MAF body. Set the pot.

It is not possible to check a MAF's calibration other than with a flow jig, because the accuracy of calibration required is +/-2%.

The MAF checks in the W/S manual and my web site are for gross MAF failure only.

byrdman454

I reset the pot to 500 ohms. It was about 625 when I started. THis change did not make any difference. The problem is not apparent when starting or idling. It seems fine. It is apparent when driving. The car wants to "buck" excessively until you wither let off the gas or give it alot more.

Can I swap the MAF with the one from my '88 S4? I need to be sure I do not damage it.

Th Euro only has about 90K on the clock. ARe MAF failures due to age, mileage, what?

Thanks

byrdman454

I taped off the MAF and forced air into the Y-connector on the drivers side as tv suggested. It is holding vacuum. This is not the problem.

Any more suggestions? Does anyone know if Autozone or NAPA has a fuel pressure tester that will work on the 928?

Thanks

tv

If you are lean you want to adjust the maf towards 1000 ohms to richen things up. I think you should exchange your maf with a known good one. If no success then exchange the lh with a known good one. Maybe one of your sensors is starting to go, like the idle/throttle switch on the side of the throttle body or a temp sensor.

The 85 euro test plan booklet might help, it tells you what to test and how and what the readings should be. This is going to be a step by step process. Like dog says, knowing fuel pressure is always helpful to.

byrdman454

John,
How much do you charge to check my LH MAF, and how much for a replacement?

Thanks

John Speake

Hi Mike,
The idle mixture pot does just that - it has the most effect at idle, and a rapidly decreasing effect higher up where you have the real problem.

My rebuilt MAFs are stocked by 928 International, the price is 350USD exchange. They have stock.

90k miles is well past the typical mileage for an S2 to start playing up due to MAF ageing. This depends on the length of journeys. The more journeys, the more burn off cycles, the more rapid the ageing

Yes, you can swap out the MAF with a MAF from a later year 928.

Regards

byrdman454

I was able to check the fuel pressure. It is setting at 29-30 psi at idle. I also swapped in my MAF from my S4 and things seemed to get better. I still have the "bucking" going on, just not as much as before. What now? I have heard that all Euros run lean, but do they run lean enough to have the car "buck" once in a while like it is starving for fuel? What else can I check?

I can't imagine the Euros would run so lean that the car would "buck", unless my S4 MAF is a little out of cal. My S4 seems to run fine. Anyone else have any suggestions?

Thanks