2.7i rough idle and intermittent hard starting

[e30jake]

Car is a 1/88 325. It ran fine before I replaced the head gasket, just leaked a little. I used a head off of another car, which was cleaned and resurfaced. Just to make sure I didn't leave anything out, the fuel system components from an "i' car that I used are:

AFM
Throttle body
TPS
Injectors
Fuel pressure regulator
Intake manifold
Cam (obviously)
ECU

The car will start and idle on its own, but runs really rough. I can pull the wires off the spark plugs on cylinders 4, 5, and 6 with no change. I have used 2 different sets of wires, and 2 different distributor caps with no changes. I have confirmed that all the plugs do have spark, and the plugs do smell like fuel if I remove them immediately after running the engine. Compression is 150 psi across all cylinders. I have a new cap and rotor on the way (even though I doubt that is the whole problem,) and I am planning on doing the screwdriver test on the injectors tonight. I do still have the seta injectors, so I may try swapping them in as well. I have tried screwing with all the different vacuum hoses while it is running, and haven't found anything that changed the way it ran. There was a thread on e30tech that had a similar problem (only running on cylinders 1-3,) which was fixed by using his old injectors. Is there something obvious I'm missing here? Thanks

That was the first problem. I fixed it by putting the original injectors back in. It ran great for a couple of days, then one day I went to start it and it cranked for a good 8 seconds before starting. Once it did start, the idle was pretty rough, enough to be noticeable while sitting in the car. I figured it might just go away, so I have been driving it (not all that much or that far) that way for the past week or so. It does seem fine once you get going, just pretty rough at idle. It has not gone away, so I figured it is time to post again to get some suggestions. Symptoms again are hard starting and rough idle which smooths out under revs. So far, the only thing I have done is taken out the fuel rail to make sure I didn't get one of the injectors dirty when I put them in the first time. Put them back in with no change. I know someone is going to tell me to do a smoke test. I'm looking for other suggestions first since I would rather not take it to a shop or go buy a smoke machine. I'll try to take a video tomorrow to see if it shows what is wrong. Any other ideas?

[jlevie]

Misfires on that set of cylinders will be plugs or injectors.

[e30jake]

Forgot to mention that I put the spark plugs in different cylinders with the same results. I guess that means I need to look more at the injectors. Will I lose anything by running stock seta injectors rather than the "i" injectors? I'm in class right now and can't really search very well

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[Mr. Tasty]

is it only running off the first three cylinders closest to the firewall? Maybe a fuel pressure issue and fuel is only getting that far down the fuel rail?

[e30jake]

It is running on the 3 cylinders farthest from the firewall. I need to find my fuel pressure gauge, but based on how much squirted out when I disconnected the fuel feed to the rail the pressure seems good.

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[SmokeE30]

Does sound like an injector issue, the stock seta injectors will work to test if that's your issue. Also check the wiring to the injectors including the c191 i believe it's is under the intake manifold connecting the injector harness to the rest of the engine harness.

[bmwstudent]

is it only running off the first three cylinders closest to the firewall? Maybe a fuel pressure issue and fuel is only getting that far down the fuel rail?

no

[e30jake]

Didnt have time to work on it until this afternoon. Jlevie was spot on (as usual.) Put my old injectors back in and everything is all good. I guess the i injectors i got were bad. Glad to finally have it done

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[e30jake]

First post updated

[Mr. Tasty]

no

what do you mean "no"

[bmwstudent]

what do you mean "no"

the fuel rail is a hollow piece of metal, if it was only half full there wouldn't be any pressure in it.

[e30jake]

Tested all the sensors at the ECU plug. Everything read what it was supposed to except the TPS at full throttle, which wouldnt effect the idle (right?) It seems more and more like a vacuum leak. If I unplug the vacuum line from the inake manifold to the FPR nothing changes, which doesnt seem right. I have replaced the FPR with a known working one without any changes. Along with rough idle, it also starts hard sometimes for seemingly no reason at all. Warm or cold outside, warm or cold engine, doesnt matter. I already cleaned the four main grounds. Not really sure what else it could be, but it never did this before the head swap. I have also noticed a major hesitation/bogging every once in a while when Im driving it. Throttle goes in, nothing happens except for a little bit of the car shaking, then it starts to pull. Usually happens between 1500 and 3000 rpm. I am planning on buying a smoke machine to do a home smoke test in the near future. Anyone have any other ideas?

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[dnguyen1963]

A real smoke machine? That's a lot of $$$. I'll try DIY smoke machines first, cheap, and easy to make.

[e30jake]

A real smoke machine? That's a lot of $$$. I'll try DIY smoke machines first, cheap, and easy to make.

That's what I meant. One of the cheap ones. If I had the dough for a real one I would just be paying someone else to figure this out lol

[603Racing]

Does sound like an injector issue, the stock seta injectors will work to test if that's your issue. Also check the wiring to the injectors including the c191 i believe it's is under the intake manifold connecting the injector harness to the rest of the engine harness.

+1

c191 plug can get corroded and cause all kinds of weird symptoms that can mimic multiple issues. Worst of all, it can be intermitent making it harder to diagnose. It's directly under the intake, round plug that screws together. There have been a few recent threads on this topic. Search for c191 and look at threads within the last month.