Hello everyone. After much searching through this forum and other popular forums, I have decided to post here about my problems as a last resort. I bought a 1989 740 Turbo wagon with the M46 transmission. As I am driving it one day, the intercooler hose pops off and there is smoke coming from the engine bay, as well as oil coming out of the exhaust. The turbo had seized, and was puking oil into the downpipe. The 13c turbo was already showing signs of going bad, and I already had a 15g set up and ready to drop in along with a yoshifab oil return bung and a braided oil feed line. Installing it was no problem, there was no more smoke, and everything appeared to be working fine, until I took it on a test drive. It had no power and could barely make it up a hill. It seemed like it didn't want to accelerate. Maybe my cat was clogged due to my old turbo leaking oil. Removing the plug before the cat made no noticeable difference, but to be safe I disconnected the cat from the downpipe. This also made no difference. Discouraged, I started thinking that maybe I was having fueling issues and discovered from this forum that the in tank fuel pump on these LH 2.2 systems tends to go bad, as well as the fuel pump relays solder joints tend to crack. When the car was idling, I could not hear the in tank fuel pump running from the access panel or from the filler pipe. I figured I would test both fuel pumps by jumping the 30 to 86/2 pins under the relay. To my suprise, I could hear both pumps buzzing strong. It must be the fuel pump relay then, what an easy fix. One new fuel pump relay later and I still cannot hear the in tank fuel pump running while the car is running. I also checked both fuel pump related fuses and they were fine.

Does this mean my ECU is messed up? It is the -541 version for the LH 2.2 turbos, which I thought weren't supposed to have problems. Are there other things that could cause the in tank fuel pump to not run, such as the o2 sensor, hall sensor, or coolant temp sensor? I really have been beating my head against the wall trying to figure out what is going on with this thing, and I feel I have reached a point where all I can do is throw money and parts at it. Any help would be greatly appreciated. Thank you.

 

Blaming the ECU is the last refuge, very rarely valid.
So, what's the issue, no power?
If you were OK prior to the turbo change, I'd look into the turbo and related.
A bad fuel pump relay won't let the car run at all.
The intank pump is a "lifter" only... Fill the car up, see if there is a difference.
I think your problem is not fuel pump related...

 

Thanks for the response. I agree, I would think the ECU should be fine. Jumping the pins to make the pumps run also led me to believe that it wasn't fuel pump related, but I swear when the car is running I can't hear the pump running. When I put my hand on the hoses coming from the in tank pump I can feel a slight vibration, but I don't really hear anything. It is much quieter than when the pins are jumpered.

The issue is the car has no power when under load ad it's especially bad when trying to go up a hill. Even when the car is idling it is hesitant to rev when the throttle is opened.

The car was running great until the intercooler hose coming from the turbo popped off while driving one day from what I figured was a seized turbo due to the oil coming out of the tailpipe and smoke. With the new turbo on, there is no smoke and when driving the car it does boost to 5 psi (going downhill when the engine has little load).

I filled up to half of a tank the other day and it made no noticeable difference. Oh I also pulled the in tank fuse while the car was idling and I did not notice a difference.

A thought I had today: Could the O2 sensor be fouled due to the old turbo coating it in oil?

Thanks again.

 

downhill with no load, there should be little or no boost. you get the most boost going UP hill at midrange RPMs and wide open throttle.

 

Appreciate your input!

I would be lucky if the RPMs got above 3000 while going up a hill, or even on flat ground for that matter. It just seems like it has no power or isn't getting enough fuel. A vacuum leak would make sense, and while I have replaced all of the smaller vacuum lines going from the CBV and wastegate, I did not check the couplings for the intercooler pipes.

Okay, I checked them by clamping each end onto a spray paint can and a wooden dowel and squeezing the longer coupler (very scientific). The throttle body side tubes I plugged the PCV port with my thumb and squeezed and there was a hiss. A loose clamp. After tightening down it passed the squeeze test.

I can't test it tonight but if that is the only problem I'll feel real stupid!

 

when you step on it hard to accelerate, what does the turbo gauge show? it should pretty quickly go to about 50% of the way between middle and the far right, and stay there until you back off on the throttle

my 740T at one point had an issue where under heavy boost and acceleration, it would suddenyl lose power until I backed off on the throttle... turns out it was sucking the rubber air INTAKE hose off the clamp right at the turbo, so air was bypassing the air filter and MAF.

another cause of lack of power is the spark advance, I don't know how that works on LH2.2 740's (LH 2.2 240's have a chrysler ignition controller that has a vacuum bellows on it).

yet another cause is fuel starvation.

also, the timing belts have been known to slip a notch or two, and put the cam and spark timing way off, maybe your belt is shot, or not installed correctly, or the timing belt tensioner isn't working right.

 

When I step on it and it managed to get enough RPM to build boost it was about halfway on the dash boost gauge. I have a secondary boost gauge connected as well which reads 5 PSI when trying to accelerate. I will make sure to tighten down everything.

As far as the spark advance, that is something I had considered. I think it is adjusted with the knock sensor perhaps. I read about the test LED you can build to check the ignition system but haven't gotten around to that yet.

I felt like it was fuel starvation, but the buzzing of the fuel pumps make it seem like they are both working, although I feel like I can't hear the in tank pump running while the car is idling.

The timing belt, tensioner, and harmonic balancer were all replaced before installing the new turbo.

I am hoping the loose clamp on the intake manifold tube was the problem. I should be able to test drive again tomorrow.

Thanks!

 

a 740T should build full boost as low as 1500 rpm, at least the later ones with the mitsubishi turbos. there was very little turbo lag on either the 91 I drove a little or the 92 I drove a *lot*. max boost is around 7 psi, past that the waste gate cuts in and keeps it even. at idle there should be about -7 psi of vacuum.

 

Thanks for the info. It seemed to be consistent at 5 PSI which is less than 7. I didn't notice the RPMs the boost built but it felt around 1500 or 2000. This could be because of the 15g wastegate actuator bracket I created for the low boost pressure. Not too concerned about the relatively low pressure right now and I might bump it up a little bit in the future once the car is driveable.

At idle it pulls -17 inHg which I guess is around -8 PSI. I noticed that as I let off the throttle on the last test drive that it would drop to about -19 inHg and the car acted like it wanted to stall, then increase to -17 and then engine would recover.

Would a loose clamp at the intake manifold tube cause all these problems? I guess it could mess with the FPR and CBV vacuum and the other vacuum things connected there.

 

ANY air leaks would cause these problems. if ALL the MAF measured air doesn't get to the engine, then its injecting the wrong amount of fuel, and things go sideways fast.

loose clamps downstream of the turbo could cause boost air to leak.

another thing, any time you remove the throttle body, use a fresh gasket for throttle body-to-manifold.

 

Thanks pierce. It would make sense that I thought I was having fuel starvation issues because I probably was due to all of the unmetered air getting into the engine.

So I tightened everything down and wouldn't you know that my loss of power problem is all gone. Boost builds at 1500 RPM and stays at 4 PSI which I think I will bump up to 8-10 PSI later tonight with a MBC.

Moral of the story: Be better than me and check every clamp for tightness and every vacuum for leaks before checking anything else.

Thanks to everyone on this form for helping everyone out like you do. I have been lurking on here since owning my S70 T5 back in 2008, and now I am back here with my 745T.