Hi all. really appreciate this site. For intro's, I cut my teeth in the early 60's on GE turbines,Lycoming apposed 6's, and Pratt&Whittney radials-1800's-2800's and the really big mothers with twin turbos the size of small garbage cans, all thanks to Uncle Sam. My total rebuilds have been mostly detroit iron,with the exception of a couple of VW,s. I guess at 60 we turn stupid. I rescued a dead '88 740 b230f from the boneyard to replace my beloved '85 caddy.

Situation so far brought it to life, thanks to your FAQ's, with a rebuilt distributer and Huco ign amp [power stage--whatever] Replaced as out of specs or unreliable following items alt amm ect sensor knock sensor coil
plug and coil wires ox sensor fpr fp check valve and filter.

Did the whole tb-intake man-oil trap-flame trap-tps and iac thing. Had the injectors cleaned and tested. Set timing and idle speed [ after replacing crank gear with broken tab and worn index tang, as well as slipping db crank pully].

Cleaned and tested all grounds, batt and alt connections, engine compartment connectors,[harness and sensor] Performed all tests I could find at ecu and icu connectors, power stage, amm, hall effect, tps etc-etc-etc. compression is 152 across the board. valve lash is withih specs & cam shows no wear. No vacuum leaks [tested with propane, light oil,carb cleaner, and stethascope. No exhaust leaks. fp's both working, fuel preasure and flow ok at all rpm.

problem is [at last you say] a random rolling miss that starts about 1900rpm and intensifies to a fullblown hairball at 2900-3000. It does exactly the same with any combination of two ecu's [one a rebuilt] and 3 icu's [all used]. Tach with inductive pickup shows plugs all firing--- but tach will jump higher each time it occurs, more so on #3&4. timing light with inductive pickup shows steady advance until hairball and then just wavers-no definate step retardation to indicate knock sensor coming into play.

Well Ladies chew on that a while and let me know what you think. Thanks ahead of time.
RJ

Have you try'd another coil???

Sorry guys in the krankenhaus for a few days - the Docs all made their boat payments and as Mark Twain said about smoking, drinking, and cussing "in two weeks I was cured! Whereupon I immediatly took up these delicacies."

In answer to the question about the coil -the coil is a brand new Bosch-the correct part# for the car-primary reads .8 olms and the secondary 11.07K olms. No hairlinr cracks, carbon tracing, swelling or leaking, contacts are all clean and shiny.

Has anyone experienced problems with new Huco power stage units? The one I purchased and installed seems to git fairly hot after running at 2000 to 3000 for a couple minutes whilr the stumbling is taking place.

Have try'd another coil???

Glad to hear I'm not the only one with this miss problem after similar detective work. Right now i'm leaning toward a bad wiring harness on my '86.
I have not checked the wobble in the distributor. How common is this?

Mike in Tacoma.
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In Tacoma '86 245 200K+ and '86 740T- 215K+ both with M46

Does that miss come in under load or just with the car stationary and no load?

'morning Doug Under load the car has fair power up to 1800 rpm in all five gears and all load situatuons. after that the stumbling increases rapidly and it is hard on my nerves to push it over 2000. what do you have in mind?

RJ

Thanks again guys I'll try to reply in order
Gary The new plugs and the old plugs that came with the car are Bosch WR7DC's After running first at idle for five minutes ant later at 3000 rpm for five I checked the plugs Center and side electrodes are clean, insulators are white, and outside metal ring is black and somewhat wet but not oily. All plugs look exactly the same. .checked owners manual calls for Bosch W6DC's I believe that is a non resister and one step cooler plug I'll check it out

Randy I manufactured a T fitting for my fuel preasure guage. Preasure is on specs static [engine off with fpr jumped] preasure holds steady at idle up to 3000 rpm----increases properly during acceleration , when vacuum to regulator is removed and blocked,and dramatically when return line is pinched both at idle and 3000 [the highest I care to rev an unloaded engine]
ever watched a cat cough up a hairball? doesn't stop what he is doing--just sputters and stumbles about-closest I could get to a good description.

Chris the hall sensor in the rebuilt distributer is new but i would like to find a way to monitor its output to the icu in real time

I did the cap and rotor change and iac bypass I described in my last posts and there was no change. Thats two less possible causes. keep'um coming guys.

As always thanks ahead of time
RJ

Do the 1988's have a Hall Sensor in the distributor? (I have a 1990 with Crank Sensor, so I don't know.) If it's got a Hall Sensor, maybe it's allowing the timing to jump all around, or I mean, get a hairball.

You seem to be leaning towards an electrical problem in the system. Is it possible that you are fuel starving? You did not mention it but I assume that you replaced the fuel filter? How were you able to determine sufficient fuel flow at higher RPM's?

Full blown hairball? Is that military jargon :-) Stumbling, missing, sputtering, etc? If you think it is an electrical problem maybe it is a good candidate for tests on someone's engine analyzer?

This is very much like bringing home a dog from the local shelter! Good luck with your project.

Randy

New (bad) sparkplug snuffing out? Are they Bosch?
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Gary Gilliam Sumerduck VA, '94 940 na Regina 160k '86 240 190k

You've been a busy guy. Looks like you've done a really thorough job. Could this be a worn/wobbly distributor shaft or maybe a cracked or loose dist cap?

Thanks for the input fixit. The dist. is a german rebuild with new Bosch cap and rotor. no visible cracks or carbon tracking and no decernable wear or wobble. I spent Friday examining every mm of it and rechecking my install and timing [I could feel Hans und Franz clucking their tongues and saying 'you vill do it dis vay, it vill not hurt"] No change. I'll scrounge up another cap and rotor and give that a try. In a standard [non electronic]ign system the problem would definately be in the secondary. I'll let you know.

Some questions that bug me. How reliable are the -211 icu's? the 3 I have are all the same age. What are their common faults and how do they identified?
Can the Hall effect signal to the Icu and the Icu signal to the power stage be monitored in any way with engine running?

Again, thanks ahead of time for any imput

RJ

Or a leaky vacuum line...

Klaus

Thanks Klause I've been through all vacuum lines with no leaks, but I wonder if the iac could be leaking while the engine is off idle? Static tests and tests on idle show it to be acceptable. Static tests on tps also ok but both were full of crankcase effluent before cleaning. I'll ground out the red-white,set the idle with the idle speed control, plug the iac ports on the intake man and intake tube and give that a try.

RJ

The IAC valve device should be free enough to rattle around when you flip the IAC back and forth. You can test it by putting 12 volts on the center pin and then grounding each side pin one at a time. The valve should quickly change positions. Could you have an intake manifold leak? Loss of hall effect signal would cause the tach to take a dive.

Thanks fixit I had preformed those tests when I cleaned the iac my train of thought came after testing all possible intake leaks. I know the iac should be closed off idle but just incase I wanted to test that dynamically I grounded the red white--set the idle with the base idle adjustment screw-- removed the iac hoses from the intake man and the intake tube--plugged both ports---ran the engine at idle up through 3000 the stumble remained the same

yesterday I dug around and got out my engine vacuum guage [seldom used by mechanics anymore] I connected it to the port for the vacuum accumulater/climate control to get manifold vacuum w/o disrupting other vacuum systems

engine pulled a rock steady 20.5psi at idle and 21.5 at 2000 no indication of intake leak or exaust blockage no fluctuation to indicate individual cylinder problem. I was interupted before I could do cranking tests or observe its actions during stumbling but will do that today.

thanks for the imput I may have done many of the things you guys suggest but it makes me rethink my results and be more accurate with my testing. I really do appreciate everyones imput

thanks
RJ