Terrible cutting out/bogging down at 3500 - RESOLVED

[jlevie]

You have been dancing around this problem for way too long and have the data that tells you what the problem is. Namely that the fuel system isn't able to keep the rail fuel pressure where it has to be.

The causes of this could be:

A rusty tank that is starving the pumps
A obstruction n the fuel supply lines
A bad transfer or high pump
A clogged or collapsed filter
Intermittent pump operation

The fix is relatively easy, though you will have to do the diagnostic work to find what needs to be fixed.

[Andy348]

Bought a new tank, installed it today along with a new fuel filter. No change at all. Got even worse at times. Fucking pissed is an understatement - just want this damn thing running already.

Took it out to check out the problem more and it completely died about half a mile from home. There's spark to the coil, spark to the distributor cap, but no spark going to the plugs.

So either the distributor cap is fucked and I've got a fuel problem, or the distributor will magically fix it.

[dnguyen1963]

If you have sparks at the cap, but none at the plugs then I would suggest that you look into getting some new wire. However, fuel pressure dropping down to zero is a big problem. Have you looked at the fuel lines? They might have cracks in them causing you to lose pressure.

[Andy348]

I've got a lead on new plugs, rotor, etc so that should be swapped soon.

Pulled off the distributor cap, there were metal shavings around the rim. Two or three of the contact points seem to be really worn down and 'hit' by the rotor. I adjusted it and then I had spark, so the car starts and drives. I unplugged the FPR vacuum line to the intake manifold and put a bolt in it. The fuel pressure now stays constant at any RPM, but I'm experiencing terrible bucking and such at around 3200rpm.

Thinking of the FPR as being my problem now, even though I've replaced it before.

[jlevie]

Tee a gauge in, zip tie it to a windshield wiper, and see what the rail pressure is while driving the car.

[Andy348]

Tee a gauge in, zip tie it to a windshield wiper, and see what the rail pressure is while driving the car.

Just did that.

Same as before - I get ±40 at idle, then as you accelerate it drops down to 25. If you continue to accelerate it'll go all the way down to ten. However, if I accelerate very lightly, shifting before 2000 rpm, I can get it up to 60-70kmh no problem and cruise in fourth at 2000rpm with 35-40 psi.

[Andy348]

Oh and the mid-line high pressure pump still squaks while I drive the car. I'm trying to get a test light there to see if it dims when I lose pressure, but it's difficult to do with the car moving. Also, I've got the old pump that I replaced with the one in the car now that I can try out.

[jlevie]

Just did that.

Same as before - I get ±40 at idle, then as you accelerate it drops down to 25. If you continue to accelerate it'll go all the way down to ten. However, if I accelerate very lightly, shifting before 2000 rpm, I can get it up to 60-70kmh no problem and cruise in fourth at 2000rpm with 35-40 psi.

The high pressure pump is bad or there is an obstruction in the filter or high pressure line to rail. The FPR could be a part of the problem, but with normal pressure at idle it sounds like it may be okay.

What you are seeing is a pressure drop with increased flow through the injectors. The pump just isn't able to provide enough flow to keep the pressure up.

[Bretts85E30]

just an fyi make sure the timing cover where the cap mounts too is fully secured theres a bolt on top on the exhaust side its 10mm that bolt usually is stripped out in the head that.

without that bolt tightened down all the way my rotor ate through 3 of my spark towers and destroyed the cap but i tightened down the bolt properly and havent had a problem since. so make sure that bolt is tightened before going nuts about why ur rotor ate up ur cap.

[Andy348]

Got a new distributor cap and new plugs throughout. Went to start it today and I've got no fuel and no spark. Only thing I replaced since it was last working was the CPS and the aforementioned items. The cps I took out of the car was cut up by the water pump pulley so I put in my old one that seems to be in rougher condition but OK. Tested it across pins one and two with no ignition and got ~530 ohms, which is standard as per the Bentley.

I've also swapped the two connectors (CPS and Impulse? sensor) to no avail.

So what could cause no fuel and no spark with what I've changed? Could the CPS be fried even if it reads correctly?

[jlevie]

To eliminate the CPS as a possibility, replace it with a new part. And yes, it can ohm out okay and still not work properly. To prevent damage to the new CPS, replace the plastic wire chase that it should be routed through across the front of the timing cover.

[rhE-30]

Can anyone elaborate on how to do this, mainly which type of gauge to use.

I'm having an issue where the there is intermittent power loss, feels like misfires, under load/acceleration in the middle of the rev range.

I have replaced the transfer pump and fuel filter recently. Cap and rotor look decent. Spark plugs and wires have been changed within five thousand miles. I'm gonna double check the plugs.

Tee a gauge in, zip tie it to a windshield wiper, and see what the rail pressure is while driving the car.

[smackley]

To tee in a fuel gauge, remove the fuel line from the rail. Tee in the gauge there and not on the return line exiting the fuel pressure regulator. The fuel rail feed line is right next to but slightly below the FPR towards the rear of the car by about an inch.

I am having similar problems to what you've described but you can follow my current steps taken to rule out a few possible items...

http://www.r3vlimited.com/board/showthread.php?t=255340

Can anyone elaborate on how to do this, mainly which type of gauge to use.

I'm having an issue where the there is intermittent power loss, feels like misfires, under load/acceleration in the middle of the rev range.

I have replaced the transfer pump and fuel filter recently. Cap and rotor look decent. Spark plugs and wires have been changed within five thousand miles. I'm gonna double check the plugs.

[rhE-30]

can this fuel pressure tester be used?

http://www.harborfreight.com/automot...ter-92699.html

[Andy348]

Well I (should say we) fixed the problem. Finally.

A fellow R3V member, sweet6e30 (John), provided all the help I could need to get the car back on the road. He came to my place three or four times to help diagnose, swap parts, fix things and even drive to various parts stores for me because I was without a functioning car. Without him I'd still be pulling my hair out trying to fix the damn thing, so mad props to him. :nice:

The problem was still complete bogging and loss of fuel pressure under load. With his help (or rather him with my help), we removed the small whateverthefuck rusted piece that was located next to the in-line high pressure pump, thinking that it could cause an obstruction. We (John) then took the guts of a '90 fuel pump that wouldn't fit the car and swapped it into the 86 pump. Next step was removing the unnecessary high pressure pump and replacing it with some hard fuel line. The new distributor cap was put in at some point, the leaking FPR was replaced with a new FPR and fuel rail, and a new CPS was installed.

It's because of this I can't say 100% what the problem was (distributor cap, fuel pump(s), CPS, FPR, etc) but I can say with certainty that the car is definitely drivable now and better then she ever was. If I was forced to guess, I'd say it was a fuel pump issue due to rust as suspected. The reason it was so hard to diagnose was because I replaced both pumps before I discovered the extremely rusty tank, so I killed the two original pumps plus the other two.

Here's a pic I took of John's E30 in front of mine at my friends house while he's changing the fuel pumps.





Getting her up to redline for the first time in the year since the swap was the highlight of my week.

Thanks to all those that offered there help in the thread and I hope this will serve as a guide to others experiencing the same problems. :)