Hard Cranking Problem

[choochbamboozle]

Having a hard start problem with my 1986 944T (2.5). Engine completely rebuilt, running a pre-Lindsey Rogue M-Tune (80# injectors, 3-BAR FPR, pump gas), early Rogue Tuning DME. Intermittent (75% of the time) very hard/slow cranking when starting up. I checked all of the battery cables, wires to starter and grounds and they are good (voltage drop, continuity). Starter/solenoid and battery are good/newer. Checked speed and reference sensors ohms at the DME and they are good (gapped with Dave Gunderson’s tool). Replaced the ignition switch a few years ago.
I removed the fuel pump fuse and pulled the coil wire while cranking and testing the wiring. Without fuel and spark, the hard cranking disappeared. So, I’m thinking it’s either an issue with my DME or fuel system. Despite the hard cranking, the engine starts, and it runs very smooth. Timing mark at TDC is spot-on and the AFM looks good when running according to my wide band. Looking for suggestions.

[Tom]

Having a hard start problem with my 1986 944T (2.5). Engine completely rebuilt, running a pre-Lindsey Rogue M-Tune (80# injectors, 3-BAR FPR, pump gas), early Rogue Tuning DME. Intermittent (75% of the time) very hard/slow cranking when starting up. I checked all of the battery cables, wires to starter and grounds and they are good (voltage drop, continuity). Starter/solenoid and battery are good/newer. Checked speed and reference sensors ohms at the DME and they are good (gapped with Dave Gunderson’s tool). Replaced the ignition switch a few years ago.
I removed the fuel pump fuse and pulled the coil wire while cranking and testing the wiring. Without fuel and spark, the hard cranking disappeared. So, I’m thinking it’s either an issue with my DME or fuel system. Despite the hard cranking, the engine starts, and it runs very smooth. Timing mark at TDC is spot-on and the AFM looks good when running according to my wide band. Looking for suggestions.

When you say hard/slow starting, I assume you mean the motor is turning over at a very low rpm and not cranking at normal speeds? If so, then most likely your issue is in the battery, cables, grounds, and/or starter motor itself.

Hard to equate slow cranking with the DME, fuel system (or engine management in general) --especially if the motor runs fine once started. Can you repeat that over and over, or was it just a one-time thing when you disconnected the coil and fuel pump fuse? I guess it's possible one of those components could be shorting out intermittently and diverting battery power away from the starter, but the odds of that seem very low compared to the traditional slow-cranking causes -- either the current (amp) isn't getting to the starter due to the battery or cables/grounds, or the starter itself is going bad.

I'd take a very close look at the cables and ground points, and try charging the battery overnight before starting. I wouldn't take much comfort from the battery and starter being newer -- I've had a battery go bad in 18 months, and got 3 defective starters in a row (!!) before giving up and finding a unit rebuilt by Bosch itself. Lots of auto parts stores will test starters for free -- although I worry their machines are mostly set to the "sell them a new starter" setting. I also had a starter cable burn inside due to a short -- literally to the point of ashes -- yet it still had perfect continuity thanks to the few strands that were still intact....

[icb]

Try posting a video of the issue. I'm just thinking out loud, cause I've never worked with turbos or an aftermarket ecu, but If there is really no significant voltage drop at the starter while cranking, and the issue disappears without the coil connected, what immediately comes to my mind is what happens when you start an old distributor-based motor with lots of initial spark advance dialed in. Maybe check the spark mapping??
Also I wonder if it could be the shielding issue on the speed /reference sensors. That tsb was about hard starting.

[choochbamboozle]

I purchased a new battery and ran a few more voltage tests. My other battery was still in decent shape but was several years old. So far, I have tested both the battery and the positive cable while cranking. With removal of Spark and fuel, while cranking, I am only seeing about a one volt drop at the battery. No big deal. When I add just spark, I get the same result. When I test with fuel and no spark, same result. Drop is to about 11 volts while cranking and it turns over fast. When I add fuel and spark, I am getting a large drop at the battery (new) to 8 volts and very slow and hard cranking. But it doesn't happen every time I crank it. Probably 90% of the time or better it cranks hard. I did a drop test on the positive cable while cranking using the same parameters as above. No issue until I add fuel and spark. I am getting .90v drop at the starter and slow, hard cranking, which I believe is no good. No fuel and or spark and I am getting a .18 V drop at the starter with easy cranking. I took -3 degrees of timing out using FQS switch and no change. Going to keep on testing and will advise. Thanks

[Tom]

I purchased a new battery and ran a few more voltage tests. My other battery was still in decent shape but was several years old. So far, I have tested both the battery and the positive cable while cranking. With removal of Spark and fuel, while cranking, I am only seeing about a one volt drop at the battery. No big deal. When I add just spark, I get the same result. When I test with fuel and no spark, same result. Drop is to about 11 volts while cranking and it turns over fast. When I add fuel and spark, I am getting a large drop at the battery (new) to 8 volts and very slow and hard cranking. But it doesn't happen every time I crank it. Probably 90% of the time or better it cranks hard. I did a drop test on the positive cable while cranking using the same parameters as above. No issue until I add fuel and spark. I am getting .90v drop at the starter and slow, hard cranking, which I believe is no good. No fuel and or spark and I am getting a .18 V drop at the starter with easy cranking. I took -3 degrees of timing out using FQS switch and no change. Going to keep on testing and will advise. Thanks

That's curious for sure. Need to mull that one over for sure... Maybe @FTECH9 has an idea if the DME is somehow part of the draw? I'd be curious what happens if you pull the spark plugs out and try cranking with fuel and spark? Or pull the plug wires off the plugs and test with fuel and spark -- just to see if you can get any clues as to whether it's purely an excessive electrical draw somewhere or if the motor is firing in a way that makes it hard to turn?

Also, how are you pulling fuel and spark when you test without either or both of those? Maybe there's a clue there?

[icb]

It's pretty normal for the voltage to drop from above 12 to around 8 or so with a normal cranking load (good battery, plugs in, ignition on, fuel present, normal compression). There are a couple hundred amps flowing and the slight resistance of battery-starter leads and connections in good condition will cause this drop (voltage= current x resistance).

The TSB I mentioned is for '87 (and up, I think) cars. I know you have an '86, but it's probably worth double-checking your bellhousing to make sure someone hasn't swapped in a later one... The relevant page of the TSB is attached. Sorry, the right side of the text is cut off, but you should get the drift pretty well.
You can test to see if this is your issue by connecting everything up as normal (fuel, dme, dme relay, plugs in and torqued) but disconnect the speed and reference sensors. If it still labors, this isn't the problem.
.

[icb]

A cranking compression test is also in order to make sure you don't have crazy cylinder pressures happening. Also, what's the history of the starter itself?

[choochbamboozle]

Starter is new. Tried a few rebuilt ones and they didn't work very well. I did slot by my bell housing. How can I shield my sensors or the starter?

[icb]

There's a shielding sleeve that they came out with. I'm not sure how you can get hold of a couple, probably the used parts guys will sell them. It might also need a different sensor bracket. I'd definitely do the test before going down that path, so you know if you really need it.

[choochbamboozle]

I pulled the sensor connections apart and cranked the engine. It cranks easily every time. I think that rules out a high compression scenario. Guess I'll go down the sensor and bracket rabbit hole first. I can probably figure out how to shield the cables and I'll likely buy new sensors since I am digging them out. Why would the bell housing need a different sensor bracket? My bell housing is the original one that came with the car. I did slot it years ago. I should mention that I did pull this motor 12 years ago and that's when I slotted the bell housing. I did have occasional hard starting over the years, maybe 10% of the time. Now, after a winter rebuild it's more like 90# of the time.