X-1

I've put off posting this and STFA'd (searched the archives) for weeks both here, the 930 forum and PP. I've read about lots of kinds of running issues, none seem to be mine.
First, I have slight symptoms of a weak fuel pressure reservoir; starts intantly cold, takes a couple pokes at the throttle to fire hot. Once started idles fine.
Problem; from idle the engine is very lethargic. Not just dual-mass flywheel lethargic, I mean asleep. If I stab the throttle it'll respond (slowly) until it revs up. But specifically, if I depress the throttle 1/4 or so and hold there it starts to rev, falls flat for a second, then spins up. During that hesitation I'll even get a backfire "thump" through the intake.
I've already gone through for intake leaks, looking for cracked lines, O-ring is good, though will try the 'spray starting fluid on injector seals, etc' method. I need to check fuel pressures too. For what it's worth the car recently smogged very good numbers.
Throttle response once cleared out is fine, she just won't come off closed throttle or idle. This makes heel/toe rev matching and green light departure irritating.

I'm weighing the choice of getting this CIS running as well as possible with the requisite techniques for now, or just start piecing together an EFI. Being able to tune with my laptop sure has more appeal than tuning with, well, a hammer.

Thanks for your help!

Staffan

To me it sounds like you have an AFR issue, is there a way you can check your AFR when you have this problem?

With that theory in mind, I can think of few things:
- a bad o2 sensor (common problem)
- a WUR gone bad (unfortunatly a common problem)
- any other CIS/fuel related problem (need to do a CIS test, fuel pressure, control pressure), it could be any of: fuel pump (there are two), bad fuel filter etc.

There could be many things, part from intake leaks you have a number of ignition related possibilities, enrichment electronics etc. But I would start by checking AFR and CIS (including o2 sensor).
Keep us posted

Edit:
Also, starting fluid is a good idea before the relative time consuming CIS test to track down different types of air leaks, especially when you have a situation with low idle.

dholling13

Staffan has some good points above; but here are some basic thoughts:

Unplug the lambda sensor near the turbo; crank up the idle using that screw which resembles a nickel (located under the intercooler). If you are still having a problem then I would inspect the large plastic plumbing running from the CIS to the turbo; mine came loose at the track and I had to keep my foot on the throttle in order for my car to idle.

I would also check the ground connection on the left side of the intercooler which the over-boost switch is grounded to. Mine came loose one time and I had similar systems.

X-1

I'm studying Adrian's pdf again. I will also pull off and recondition my TPS. The paragraph about Throttle Switch Operation was informative.

X-1

OK, maybe an excuse to keep the thread "bumped", but I just put a 13mm socket to the intake manifold nuts... I could turn the right-side ones with just the extension. Getting to the left-side ones under the flapper housing is tough, though they seem snug.
Once the pesky airbox (tin shed) is out you can finally poke, prod and pull on the plumbing. All the vacuum hoses seem to check out.

Question: on the bi-turbo S4s we would hook up a compressor to the intake and pump in 15psi or so and look/listen for leaks (those cars are infamous for popping IC and throttle body boots). Is there a comparable technique for pressure testing our intake?

Staffan

The intake manifold nuts do come loose, happened to me and I heard about others as well. Didn't effect my engine noticeable though, but you never know.

To answer your question, not that I know of.
Perhaps someon could post a drawing on the intake system and you would be able to figure out what to pressurize and what to plug. But I must say that an intake leak sounds strange, why would the car run good once coming over this stumbling low rev situation, in my book intake leaks would make things worse with increasing pressure (boost)?

Most common intake leaks in my book is the intercooler not sitting low enough on throttle body (but you checked that) and hoses connected to the intercooler coming loose, but these kind o leaks are usually easily identified with a "woosh" sound under boost.

It would be very interesting to know what AFR you are at when the engine stumbles. To know if there is too little, too much or perfect will guide in the right direction I think.

I would look at a possible fuel problems due to some CIS malfunction (o2 sensor, WUR, fuel pumps, cold start sensor, BOV, runnover valve etc.), perhaps a first step would be checking AFR, then do the different CIS tests outlined in the workshop manual.

There are also ways described in the workshop manual on how to check ignition related stuff, like simulating manifold pressure for the ignition module (EZ69), check that air intake sensor works, that ignition module gets speed signal etc.

X-1

From my understanding, an intake leak will exacerbate low rpm issues while becoming inconsequential at higher revs because; at low rpm the total intake air volume is very low, and a small leak will throw that off dramatically, whilst at high rpms the leak is only a small part of the massive amount of airflow.

I have a wideband... sitting on my workbench. I have to find time to pull my muffler and courage to try MIGing stainless (or be smart enough to take it to a shop). I am looking forward to using the wideband. It'll be nice to have peace-of-mind when I get the tach over to the right side. And with an adjustable WUR and enrichment delay maybe I'll be able to get snappier power, better top end, more than 180mi from a tank of gas.

EDIT: and the left-side manifold nuts were loose too. My only concern is whether I should just pull it all out and replace the gaskets if it's been sucking/blowing through a loose seating for who-knows how long.

Staffan

Well, as long it's nothing that could flex/expand (like an o-ring or rubber hose) I buy-in your line of thought. Again, I belive starting fluid at idle around manifold would tell you if you have an air leak or not.

I'm using a Zeitronix wideband, log runs to my PC, great peace of mind and helpful when trying to diagnos things.

X-1

UPDATE: after tightening the manifold nuts and reassembling I started it, and it still stumbles when it's cold. You can thumb the throttle lever under the intercooler and hear and feel the CIS flapper SLAM from the intake reversion. Though it felt noticably better to drive and I couldn't recreate the stumble once hot.
So I tore it all apart. Right now the injectors are soaking in Chemtool, though I may send them out or replace them as #4 intake valve has gas pooling on it and blowing the Chemtool out with air reveals goofy spray patterns. Most of the manifold gaskets look like they've been leaking a long time, are saturated by gas and carbon residue. Service records say nothing about the diz cap/rotor, and they look pretty tired.
I'm debating whether to replace the ($300) accumulator if my #4 injector has been drooling all the system pressure... I will order the new dizzy, gaskets, and try to find a local shop that can test these injectors if possible. I'm not in the fiscal position right now to wave the Magic Visa over this and have Brown deliver a bunch of new parts, so wish me luck.

Staffan

Keeps my fingers crossed!

FVD sells injectors at 68 Euros if that turns out to be the problem:
http://shop.fvd.de/?VID=385043&VCD=7...Body=&CarYear=

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So I ripped out the entire fueling and ignition system and overhauled and cleaned everything. I ordered new dizzy and gaskets from PP. I soaked the injectors in Chemtool (mmm, tasty) all week. I very carefully lifted the injector nozzle and back-blew the injectors, then clamped a 4ft fuel line to each injector, stuck it in a Corona bottle, filled the hose with Chemtool, apply air hose, observe spray pattern. In figuring all this out I managed to pour Chemtool up my sleeve, spray Chemtool all over my face, dump several ozs on the floor... today my liver whimpers. I then reassembled the fueling system with hoses running off the injectors down to graduated medicine cups on the floor. (pics to follow)

Gathered fire extinguishers...

Propped the barn door w/ 1/4" hose, turned over the motor for ~20sec. Injector displacement was almost perfectly consistent (whew!). Though I do have a leaking injector, explaining the hot-start issue so I can stop blaming my accumulator.

I HATE the smog pump I had to pull that @#$% back out to get the injector back in. Getting the turbo inlet elbow hose back on was a PITA. The PO never installed the top nut on the exhaust flange, so I bought the 17mm crowsfoot only to discover I'll have to pull the other three nuts first and START with the top nut as the stud is too close to the pipe.
I figured the local muffler shop could do my wideband O2 bung install better than me. No. The B&B has a nice FAT 3.5" pipe off the turbo, but it bottlenecks into a 2.5" flanged hole on the muffler so I had said muffler guy open that up. I got home to discover he'd burned clear through one side of the pipe weld so I pulled out the trusty Lincoln wire feed. Why do I insist on paying good money to "professionals" when I can f*** up my stuff myself for free?
I haven't driven it yet. I wasn't about to start it at 2am when either the loud exhaust or the roaring gasoline flash fire would wake up the neighborhood...

X-1

I'm just gonna keep adding information to this thread as I discover it, hope it'll help someone down the line.
The car was definitely tuned up "around" the intake manifold leak. With that fixed it's now it's exhibiting classic base fueling problems: I cannot get it to hold 2k rpm in neutral (or drive 20mph) without it hunting up and down. Idle hangs at 1,300rpm for 10-20sec before returning to 1,000. It didn't to this before, and it idled happily at 800.
Here's the good data; The wideband shows the a/f lean spike to 15.5+ the same instant it stumbles when you poke the throttle. Fueling returns to ~14 at steady throttle and mid 12s under boost to redline, so it's just the tip-in enrichment. While I had all the intake stuff out I cleaned the contact points on the throttle position sensor... but that would only affect ignition timing anyway (?). So how does the CIS enrich at tip-in? Is this a WUR thing? I will do more research.

Staffan

You didn't adjust the idle along the path, somone suggested you should do that I think ?

Other things to check could include anything that by-passes air from intercooler to manifold, not passing the throttle body (aav and run-over valve) since you have a lean situation.

You can check the auxiliary air valve (aav) by pinching the hose on the right side of the intercooler, if the idle drops then you know where you should keep looking. The aav gives the engine extra if when cool, somtimes the sliding disk get stuck. IMO this (the AAV) is the most common thing to brake on these cars (together with the BOV), we did a poll about these things a few years back.

Another component that short-cut air to manifold by-passing the throttle body is the run-over valve, disk shaped thing underneath the intercooler. On throttle lift a valve opens and feed the engine with extra air. If you plug this thing you will get flames.

Here is a link to a document where you will find what you need about CIS, the throttle position switch and what components that use the information.
http://www.adrianstreather.com/docs/...20overview.pdf

X-1

Thanks for keeping the dialog going Staffan!
I have been studying Adrian's overview fervently. I still have a suspicious eye on the throttle-opening enrichment controls as the primary symptom is reluctance to rev up from idle and the corresponding lean spike. Another thing I'm seeing is inconsistent Lambda control. Sometimes (cruising) the lambda control is dead-on in the mid 14s, other times I'll watch it dip way down into the 11s for no apparent reason. I may try a new O2 sensor, though I detest the popular "buy new/expensive parts until the problem goes away" approach people seem to accept. I'm much more inclined to systematically diagnose, research and theorize before buying parts. Then when it didn't fix it I don't feel like a complete idiot.