Completely Stumped...

[ashton]

Alright guys, I have an 88 325i 5 speed. I've rebuilt it from the head up. All new parts including COolant temp sensor o2 sensor fuel pump fuel filter ecu coil spark plugs plug wires. All new gaskets head bolts and afm. Maybe more that I can't think of Ill go down the road and it'll run fine until it'd warm and then 3 or 4 miles down the road i'll lose throttle and the more I push it the worse it gets. Ill put it in neutral and let it coast for a minute and it'll go a lil better but not much so ill pull over and turn it off and let the fuel pump prime and start it and itk run right for another 3 or 4 miles. I've replaced everything I can think of. If you have any idea what it could be please lett me know cause I wanna drive my e30. I miss it....

Thanks.
Ashton.

[ashton]

When I turn it off and go to start it, its hard to start to. I have autolite platinum spark plugs and I heard they suck, but I wasn't sure if this would cause the symptoms im describing.

[Sagaris]

Pull the vacuum line from the fuel pressure regulator to the intake manifold and see if any liquid gasoline is present. If the diaphragm is leaking then you will get extra fuel in the manifold which can get things running rich. Also, see how it drives with the oxygen sensor disconnected. It may run fine in open loop, but once the car warms up and closed loop starts, the ECU uses oxygen sensor feedback which requires a good oxygen sensor. If the oxygen sensor is giving bad / slow readings to the ECU then you will have running problems.

Those are the quick and easy things to check, if it is not the FPR or O2 sensor then I suggest running a fuel pressure test. Even though you have a new fuel pump, there may be blockages in the feed line or the return line which could decrease or increase fuel pressure.

Make sure to post the solution when you find it.

[nando]

platinum plugs are bunk. go with copper plugs, either from Bosch or NGK. my personal preference is NGK. BPR5ES will work well.

but, it is likely not your main issue.

[ashton]

Pull the vacuum line from the fuel pressure regulator to the intake manifold and see if any liquid gasoline is present. If the diaphragm is leaking then you will get extra fuel in the manifold which can get things running rich. Also, see how it drives with the oxygen sensor disconnected. It may run fine in open loop, but once the car warms up and closed loop starts, the ECU uses oxygen sensor feedback which requires a good oxygen sensor. If the oxygen sensor is giving bad / slow readings to the ECU then you will have running problems.

It's a new o2 sensor. Should I still check? And what do I do if it is leaking into the manifold? And thanks for the reply.

[M-technik-3]

Mileage? Is the cat clogged or rattling? Fuel filter junk now?

[ashton]

platinum plugs are bunk. go with copper plugs, either from Bosch or NGK. my personal preference is NGK. BPR5ES will work well.

but, it is likely not your main issue.

What do autolites do that make them junk?

[ashton]

Mileage? Is the cat clogged or rattling? Fuel filter junk now?

The cat does rattle and the fuel filter was replaced like a month and a half ago. But I guess I should take it off and check. The cat has like 250,000 miles.

[Sagaris]

If there is fuel in the FPR vacuum line to the manifold, then replace the FPR. It is a very simple job, but the FPR is a pricey little bugger. If you are okay with spending $70+ for a new one then go for it, but getting a known-good used one off the forum here for $20 is fine.

Did you replace the oxygen sensor with a universal sensor, or one with the correct wire harness that plugs into the car normally?

[M-technik-3]

Bosch does make a nice 4 wire universal heated one, for about 65 bucks with a 1 year warranty.

My cat is currently loose and breaking up, It makes the car very tough to drive as the exhaust does not want to exit the system.

Bad thing.

[nando]

What do autolites do that make them junk?

they're platinum. platinum plugs cost more for no benefit. snake oil type stuff.

on older engines, platinum plugs typically make them run worse.

[M-technik-3]

Multi electrode type spark plugs have tighter tolerances for cleaner aka leaner burning engines.

The M20 is not a real clean burning engine so the electrodes tend to get crap in them and foul out. Nice simple copper plug can be Cleaned and reused OR cheap enough to be tossed in the refuse and buy new ones.

[ashton]

If there is fuel in the FPR vacuum line to the manifold, then replace the FPR. It is a very simple job, but the FPR is a pricey little bugger. If you are okay with spending $70+ for a new one then go for it, but getting a known-good used one off the forum here for $20 is fine.

Did you replace the oxygen sensor with a universal sensor, or one with the correct wire harness that plugs into the car normally?

Alright ill check it, and its the o2 sensor that fits the car, but the weird thing is that there isn't a check engine light...

[ashton]

Multi electrode type spark plugs have tighter tolerances for cleaner aka leaner burning engines.

The M20 is not a real clean burning engine so the electrodes tend to get crap in them and foul out. Nice simple copper plug can be Cleaned and reused OR cheap enough to be tossed in the refuse and buy new ones.

Alright thanks.

[ashton]

Bosch does make a nice 4 wire universal heated one, for about 65 bucks with a 1 year warranty.

My cat is currently loose and breaking up, It makes the car very tough to drive as the exhaust does not want to exit the system.

Bad thing.

I just hate to cut the cat off and nothing be wrong with it and I have to get it welded back on....