DFlintstone

Last week giving a hand to another poster, I jumped to the pump side of my resistor with the Ign off. Don't know if it's a coincidence or not but since then instead of the 4 count I'm used to it now and then goes toooo long. It cranks GREAT. With 300K in sight and a new bat, & starter...it might only do that cold. (only jumped it for a second)

5-90

Particularly common on RENIX (1987-1990 w/AMC engine,) and there are two probable causes...

- RENIX doesn't fire ignition or fuel injection pulses until it reads 300rpm at the CKP. This means that an old starter, low battery charge, or a dirty ground connexion can all cause long crank times (the first two will slow down the engine's ability to crank, the last can screw with the signals, even though the CKP runs straight to the ECU for wiring via C101.) There was also a TSB for weak CKP signals, where the CKP wiring gets fed directly through the firewall to the ECU, but this is often not necessary. Clean up your grounds and check battery charge.

- There is a check valve in the fuel pump, that is meant to help maintain pressure in the fuel system with the engine OFF. This check valve can fail, which means the system has to be primed before you can start your engine. Test for this by turning the key to ON for 4-5 seconds before turning it to START. If the engine starts straight away, the check valve has probably failed (the pump itself is usually an all-or-nothing deal.) You can replace the pump (it doesn't require dropping the tank,) or you can get a relatively inexpensive part from BMW (a fuel check valve - I don't recall the part number, but it's out there) and plumb it into the softline just outside of the fuel tank.

A failed/failing CKP can cause long crank times in the early stages - but that's usually a heat-related failure. This can be tested for by starting with a DEAD COLD engine, and heating up the CKP specifically with a hair dryer on LOW. Get it so it's hot to the touch, get everything out from underhood, and see if that replicates the long crank time condition. If it does, secure a replacement before it fails totally...

DFlintstone

Supper. So I have a couple things I can try. "CKP"? Is that the same as the CPS? ECU I would gather is also called the PCM. BMW I got. You got me there with TSB. A process? "Toss Stupid Bstrd"? So first thing, tomorrow I'll check the check valve. Heating the *** sensor could be a problem as it IS doing it cold. Also I had the thought to try disconnecting the batt. for a minute and letting the ecu/pcm re-boot.

A last question. Is starting pretty much right on the count of 4 (or 3),normal for, (this old renix...? it does crank very well. Thanks for your time, Don.

tjwalker

Agree with 5-90........

I'd start with freshening all engine GROUNDS. Renix are extremely susceptible to ground issues.

Can't tell a thing by looking at them. Must remove, freshen, reassemble.

And definitely try the "poor mans prime" that he suggests. Quick and dirty way of snaking out a checkvalve issue.

cruiser54

Good advice here. You can also check the CPS output voltage. It needs to be near 500 AC millivolts on cranking, disconnected from the harness. If it's down near 300 you may experience long crank times and/or intermittent crank-no start issues.
Manual trans? If so, clutch material may be on the tip of the CPS interfering with signal generation.

You could increase your cranking speed by adding 5-90"s upgraded cables at some point, too!!!

5-90

Sorry - I've been speaking the language so long that I forget. I should put on my lexicographer hat while I'm doing my site reorg...

TSB = Technical Service Bulletin. A "spot-fix" document for a known problem - the problem may be universal (affecting all vehicles of a certain year/make/model/powertrain) or not. (Granted, "Toss Stupid B*****" has been used by me in various shops...)

CKP = CranKshaft Position Sensor. "CPS" is a misnomer (the CaMshaft Position sensor is listed as "CMP.")

ECU = Electronic Control Unit. Generally applies to any purpose-built "computer" in a car, but RENIX has only the two (engine and transmission (TCU) - unless you're stuck with ABS.)

PCM = Powertrain Control Module. What ChryCo calls their engine controller generally, because it can integrate the function of previously separate ECUs. ChryCo also calls them "SMEC" - Single Module Engine Controller - or "SBEC" - Single Board Engine Controller.)

C101 is the main connector for electrics through the firewall. It was a very specific connector in early RENIX (1987-early 1988, it was under the clutch master cylinder, and a clutch leak caused massive corrosion,) but it's generically used for the primary connector through the firewall.

If the problem also occurs cold, don't bother with the "heat soak" testing (heating with a hair dryer - although a cheap hair dryer is always a useful bit of kit to have, with all of the electronics and sensors cars now have underhood. Heat-related failures are common, and a bear to diagnose without targetted heat...) It may be a fuel leakdown issue, or a failed/failing check valve (which is the leakdown issue, but the fuel leaks back into the tank.) Try checking for that first.

Grounds should be checked/serviced anytime you have an electrical problem. In thirty+ years of mechanical work, I've probably tracked some 80-85% of electrical problems to some bad ground or another. Clean chassis contact points down to bare metal and apply a proper electrical corrosion inhibitor - you'll find it in the electrical section of your local hardware/DIY store. For the love of God and all you hold holy - do not RPT NOT use WD-40! That will cause more trouble than you're trying to fix! Replace OEM hardware with CRES/stainless (sheetmetal/tapping screws) or brass/bronze (machine threads) to cut down on corrosion in the joint.

Also, on RENIX, bear in mind the following two points:
- The chassis is not grounded directly to the battery.
- The ECU is grounded to the chassis.

With that in mind, a little thing that can fix so many electronic goofy bits on RENIX is horribly simple to fix - make a short (about 12") jumper lead out of fairly heavy-gage wire (nothing less than 10AWG. If you want to match the rest of the OEM leads, use 6AWG,) with a 3/8" ring on one end and a #10 or #12 ring on the other. Attach the large ring to the negative battery post, attach the small ring to bare metal on the chassis (you'll have to clean a spot - about half the size of a postage stamp will do, use a wire wheel) using a CRES tapping screw, and apply corrosion inhibitor on assembly. The fender liner is a good point. This will provide a more direct ground path for the ECU, which will help to clean up the ground plane (or "zero reference" for sensor signals) and smooth out quite a few things.

CRES = "Corrosion RESistant alloy steel." The phrase "stainless steel" is actually an old trademark, and CRES or "CRES alloy" is really the proper way to refer to high-chromium carbon steel. Proper CRES is, I believe, at least 15% chromium by weight - which forms the layer of chromic oxide on the surface that makes it "stainless.")

DFlintstone

Thanks much 5-90. Have the extra ground. Had the leak on my 84, (fluid came out of fuse box, sweeet). Been using plain old bearing grease on connections for ?15 years? Maybe the right stuff is better, I wouldn't know how to tell.

It's during this process that I added the ground, found the problem in less then 2 years)

There is a gang of wires coming up the front of the engine that run up around the manifold heat shield to the injectors. (at least there is on my 90). The edge of that shield can cut into those wires, (when it expands, sitting), sometimes causing all sorts of problems. Mine blew the mouse nest in the air cleaner out through my front grille. Drove through the confetti! No sign of the mouse. I just moved the wires, problem solved.

I'll try the "poor mans prime" as I run around today, Thanks again, Don.

Gee oh Dee

Lots of great info here!

tjwalker

You better believe it. 5-90 is the man when it comes to electrical. Pay heed.

5-90

That bundle of wiring actually runs "down" - not "up." It's the feed for the CTS (Coolant Temperature Sensor," Knock sensor, and HEGO (Heated Exhaust Gas Oxygen sensor) underneath the intake. It's included in the F/I subharness coming out of the firewall, as is the sensor wiring for the various sensors in the intake and the CKP at the rear of the engine. (How do I know this? I spent a couple of days a dozen years back tearing that harness to bits to isolate and repair a floating ground issue. Urgh...)

Anything that leaves a non-conductive film will eventually cause problems. For multiterminal connectors, use dielectric grease (it's non-conductive so terminals don't short to each other, but light enough that it wipes right out of the way) or nothing. For single contacts, use corrosion inhibitor when they're exposed to the weather (I prefer to use Weatherpacks, Metri-Pack, Deustch, Amphenol or CPC connectors "dry" - they're all environmentally sealed. About the only exposed connections I have are chassis grounds, and they get Gardner-Bender Ox-Gard corrosion inhibitor.)

Gee oh Dee

lmfao, Already subscribed.

DFlintstone

It's lookin like the check valve. Priming it has it starting better than ever. Could be by-passing the resistor jammed the valve better than ever. Someday when I have time maybe I'll try some Kem-tool in the pump, (briefly), or some additive in the fuel.

Does anyone know, is that something I already have? ie. mineral spirits, toluene, paint thinner, mad dog 20/20 ?

And thanks for solving the problem I made myself solving a problem!

5-90

Jumping the resistor has nothing to do with the check valve - it's a separate issue (added mid-1988 for reasons of NVH, and was a "voluntary recall" before. Whimps were apparently whinging about fuel pump noise...) Out of the five RENIX rigs I've had, two didn't have the resistor to begin with, and one failed and I just bypassed it with no ill effects (my wife is like me - she likes a little noise to remind her the vehicle is running...)

Toluene will work - and will actually kick up the octane of your fuel a notch or two (toluene has an AKI of about 135, and has been used straight as a racing fuel. I've built a couple of engines that wouldn't run on anything but toluene - 120LL still knocked...) I figure a cut similar to acetone for a maintenance clean - 1 ounce to four gallons will do. Double that for a "shock" clean. Toluene is used as an "AKI improver" anyhow, so you're just changing the concentration

Acetone can also be used - it's currently used as a fuel system cleaner in most gasoline blends anyhow.

Mad Dog 20/20? I suppose that's possible - although I'm sure 151 would burn better... (I don't care much for MD. I had a stretch where I was killing a fifth of 151 in a couple of hours - I'm amazed I still have a liver!)