2.7i Conversion Issues [FIXED]

[Untouched]

FIXED: Turns out I had the TPS and ICV plugs swapped this entire time... I'm surprised the car ran at all, must have 12v and ground on the same wires. Thank you everyone!

Hey everyone,

I have recently converted my 86' 325 2.7 into the 2.7i with parts from an 89' 325i. I am currently running into some issues that I am having trouble chasing down.

The car starts up fine. I currently have the IAC valve bypassed by having the throttle set open slightly. With this, the car idles fine. Upon increasing the revs (about 1/4 throttle); the engine loses power for a second, revs up, loses power, revs up, etc. This happens at any throttle position past 1/4 open. It almost seems like fuel/spark is being cut for a second, then comes back, cuts, and comes back. If i return the throttle to the almost closed position, it idles fine again. The car never actually stalls though.

With this said, the car ran great before this conversion with all the ETA parts.

The only old ETA parts I am using are the fuel pump, plug wires, coil, cap/rotor, dizzy, alternator, o2, and coolant hoses. Parts that came from the 89' are pretty much everything from the cylinder head and back (harness, ecu, injectors, fpr, cps, tps, etc..)

What are some tests that could be done to try and diagnose this? What parts going bad could cause this to happen?


Thanks! 8-)

Update: Cleaned out IAC valve, car idles with it now, no more bypassing. Now using 325i spark plug wires with CID sensor.
Update2: Tested fuel pressure. 36psi idle, 36-40psi revs. see post #9
Update3: Replaced FPR and CPS. Fuel pressure now a solid 44psi. Video of problem: https://www.youtube.com/watch?v=wpbM_FXtxgU Shows constant rev bouncing at 2500+ RPM. (disregard exhaust, currently removed back half. hard start and stall is due to intermittent working ICV)

[Andy.B]

Check fuel pressure, and make sure you have the correct FPR.

Why do you have the IAC valve bypassed?

[Untouched]

Check fuel pressure, and make sure you have the correct FPR.

Why do you have the IAC valve bypassed?

The car idles terribly with the IAC doing all the work. Seems the internals of it aren't moving very freely, even with a good spraying of intake cleaner. I'll replace it soon, but for now it needed to be bypassed.

I'll have to pick up a fuel pressure gauge. Any recommendations?

I'd like to think the FPR that came off the 89' was the correct one. Though I guess I can't be certain. The difference between them is the 'ETA' is 2.5bar and the 'I' is 3bar correct? I guess once I get the fuel pressure gauge hooked it will tell me what we are working with.

[Regnar75]

yes. 325i is 3bar. Eta is 2.5 Bar that's important. it also says it right on the FPR 2.5 or 3.0. A few other things is the AFM's are different between the two models, and I assume you went with a full motronic 1.3 conversion. make sure you have the right AFM and you didnt adjust it.

for cleaning the ICV (IAC) spray cleaner inside and on the "walls" of the gate that spins around, manually spin it and keep spraying. you should be able to spin the walls just by moving the ICV in a lasso motion (circles to allow inertia to work) if you get what i mean.

the other thing i notice is the plug wires. the 325i wires have a reference sensor on one of the wires (i think 6) which plugs into the harness by the CPS plug. this should be corrected but I'm pretty sure the car will run without it.

I forget if spark plugs are different, maybe just the gap. double check on the 2.7i sticky.

Try and resolve the ICV issue, the TPS sensor has two switches, if i remember right, the first one tells the computer the car is in idle (throttle closed, uses ICV and Idle fueling) the other is wide open to go into a set fueling. when its in between it stops listening to ICV and goes to AFM for Fueling.

how did you do your o2 wiring? the 86 has the 3 wire o2 sensor by the guibo, the 325i motronic 1.3 has a 4 wire o2 sensor near exhaust manifolds, and also has a different connector hooking into the wiring harness.

[Untouched]

...

Yes, this was a total conversion. I have the AFM from the 325i. The resistance track under the cover is in good condition and is making contact all the way through the travel. I have no idea if it was adjusted before hand. It apparently was rebuilt recently, so hopefully that is all set correctly. It even has the cap over the adjustment screw still.

I will attempt to try cleaning the IAC valve more, maybe be a little more aggressive with it. Any particular brand of spray you recommend?

I have new plug wires coming with the CID sensor attached to cylinder 6. Apparently all this changes is firing of the spark plugs either in banks of 3 or 6. Should only affect MPG slightly, but it will be fixed soon anyway. Also have 325i plugs coming, Bosch Supers, so everything on that end will be squared away.

The TPS does have a distinct click at close. Though, I don't notice it when it is opened all the way. Unfortunately, having the TPS plugged in or not does not seem to effect this problem. Not sure if that is good or bad though...

My o2 sensor is from an older mustang. I have the 325i exhaust (no cat though) with the o2 sensor in the manifold. Followed a DIY on here on how to wire it all up. Signal goes to signal, heater wires polarity doesn't matter. Signal gets grounded through body. Pretty much it's a generic Bosch 3 wire. I ran the car for quite awhile (pre conversion) without an o2 sensor. Didn't seem to make much of a difference honestly. Currently makes no difference to this problem with/without it.

[Andy.B]

It sounds like you have a good handle on the specifics of the swap.

I usually plug one side of the IAC valve with my a glove or rag, and 'fill' it with carb cleaner, then cover the other side, shake it vigorously, and drain it, several times, to really get it cleaned out. Then follow it up with a light spray of wd40 to ensure it's lubricated. I have had good luck restoring function to even the gunkiest of IAC valves with this approach.

I honestly wouldn't even bother trying to diagnose around a missing IAC valve. The system is not that adaptive, and only has a few inputs and controls to work with. With one of them missing, it isn't well equipped to compensate for it.

[Untouched]

..

I will attempt this type of IAC clean right now. Also just got my new plug wires with the CID sensor. Let's see if those help out at all.

Quick question; the Crank Position Sensor...I know that if they aren't working it will cause no starts. Mine is within spec according to the OHM meter. Reason I ask is because when getting the engine harness, I had to cut that sensor wire and re-solder it. Even after the re-solder, it is within spec and allowing the car to start. Is it possible that when the crank is spinning faster it just can't keep up with the pulses, even though it's within spec from a resistance side of things? Just a thought.

[Untouched]

Cleaned out the IAC valve and put on new plug wires with the CID sensor. Car starts...but.. upon starting, it idles pretty low, around 500-600 rpm. While it is idling, the battery light stays on the entire time. The moment I give it throttle, it goes off. If I let off the throttle (slow or fast) it stalls pretty instantly. The battery is good, as it's the one from my daily driver. While the car is running, the voltmeter is at about 13.5 volts at the battery, so it is charging.

Is this a symptom of a bad alternator? I am using the 80 amp ETA one.. I know the 325i one is 90amp. Is it possible that the alternator is going slightly bad and can't keep up with the higher load it now has? LUCKILY, I was able to pick up a used 90amp 325i alternator from a friend. He also gave me a new voltage regulator. I am going to get both alternators tested tomorrow and see if either are good. If the 90amp one is good, I'll try that one in the car.

[Untouched]

Installed new alternator. The 2 others I had tested bad, so replaced for piece of mind.

I have tested the fuel pressure. At Idle (1000rpmish) it's 36psi. When I rev it and it starts bouncing between 2500-3000rpm as described above, it's between 36psi and 40psi. If I unplug the FPR vacuum line at idle or revs, it's 41psi.

These numbers seem low for 325i specs; should be around 46psi right? Would this psi difference cause my issue? Upon looking at the inline fuel pump, it looks like some slight amount of gas is on the bottom of the tank, not enough to drip to the ground though.

Could a very small leak on the top of the fuel tank cause the drop in pressure? If I pull the tank, should I source a 325i one with the in-tank pump? Or just find the problem with mine? Are there any advantages to the 325i tank/pump versus the 325e tank/pump?

[jeffnhiscars]

As has been mentioned, the fpr should be labeled with 2.5 or 3.0. I may have missed if you checked that but those readings seem low for a 3.0

[Andy.B]

You should check the fuel output of the in tank pump to make sure it is feeding a sufficient supply to the in line high pressure pump.

Which DME do you have? 153 or 173? Is it the stock chip? Many people report cold start idle issues with the basic 2.7i build and the stock tune. sssquid offers a great tune at a fair price.

I would work your way through the fuel delivery system checks in the Bentley manual. If everything continues to check out ok, I would have to suspect vacuum leaks.

It might help you to post some engine bay pictures to give us a better idea of what you're working with. A fresh set of eyes may see something you don't.

[packratbimmer]

You mentioned using eta plug wires. I assume you are using the cylinder reference sensor?

[Untouched]

You should check the fuel output of the in tank pump to make sure it is feeding a sufficient supply to the in line high pressure pump.

Which DME do you have? 153 or 173? Is it the stock chip? Many people report cold start idle issues with the basic 2.7i build and the stock tune. sssquid offers a great tune at a fair price.

I would work your way through the fuel delivery system checks in the Bentley manual. If everything continues to check out ok, I would have to suspect vacuum leaks.

It might help you to post some engine bay pictures to give us a better idea of what you're working with. A fresh set of eyes may see something you don't.

I'll check out the in tank pump. First I am going to drop the tank and see what up there is leaking; might aswell do it all at once and not have to worry about it again.

I am using the 380 DME. Does it have to be 173? I thought pretty much all motronic 1.3 after 173 were basically the same? I am currently using the stock chip. Was going to try and get the car running decent and then chip it, one less variable.

I'll go through the Bentley tests. I honestly haven't even looked at it.

I'll be sure to post some pictures on Tuesday when I am home, currently out of town until then. Any specific areas you would like to see?

Thanks for all the help!

You mentioned using eta plug wires. I assume you are using the cylinder reference sensor?

I now have 325i wires with the cylinder reference sensor yes.

[Regnar75]

random thought, i was having lean and bogging issues in the turbo e30 for the past few weeks and I assumed the 255lph fuel pump was working properly (it was) but the hose that connected the fuel pump to the fuel pump bracket was only on by a small amount so the fuel was sneaking by the hose clamp and spraying in the gas tank. this caused me to have 28-30psi fuel pressure.
I since reattached the hose and within 10 minutes ruptured said hose. i replaced it with a stronger hose and all my issues were resolved and am running at 43psi. i would highly suggest checking that connection again because its free and easy to check.
^just realized Andy said this basically.

[Regnar75]

Could a very small leak on the top of the fuel tank cause the drop in pressure? If I pull the tank, should I source a 325i one with the in-tank pump? Or just find the problem with mine? Are there any advantages to the 325i tank/pump versus the 325e tank/pump?

before pulling the tank just lift the back seat and check to see if the hoses are on there properly and there is no holes in the hoses. I'd recommend eventually moving towards a single in tank high pressure fuel pump for lower replacement cost, simplifying the system and having more fuel (even though the dual eta pumps will be sufficient for a 2.7i)

It is possible your transfer pump (in tank) is dying, not getting enough voltage, or even just the filter at the bottom is clogged (also your regular fuel filter i forget if you replaced it, at least bang on it with a wrench)

check for holes in those lines going to intank pump (near where your leak is) also check the intank pump hose and filter. then check voltage to the little plug that goes into the pump it will only show voltage as the engine is cranking so unplug it use a multimeter and turn the key (its possible to do solo)
if you dont have any leaks in the hoses, everything is on tight, the in tank fuel pump filter is clean, and you're getting proper voltage to the pump then i would look somewhere else for free trouble shooting before replacing anything.

under the driver side, by the high pressure fuel pump you may want to try by passing the two metal pulse harmonizers or w.e. they're called, they sometimes rust up and can cause fuel to jam up in them. just run a hose around them into the fuel pump.

I converted the dual pump setup to a single intank pump and love it, but on the Early model cars with two pumps its a little different than the write ups (our tanks are different) if you go this route message me and ill tell you what to look for and do.


also to address the CPS question,
unfortunately I dont know how the CPS will handle the solder and at higher rpms. its quite possible. if you have another used one to try it against or are willing to buy a new one thatd be a good idea in general.

I was under the same impression with the ECU's anything being 1.3, i have a 524 ecu and it works fine. I assume the same with others.

I dont ask this because I think its your issue, but it always comes into play at one point or another, but check your grounds all around.