jeff spahn

So while my car sat for months and months it developed a strange miss. When I put it on the lift it ran perfectly (yes even supercharged it ran perfectly. Smooth idle, no stumbles, no issues ). I went to move it off the lift one day and it wouldn't start without a bunch of foot feed. So. I got it running and it was running on 4 cyl. Checked the ignition protection circuit. No lights. Checked the spark. Damn near dead. Put on new caps since I had lying around. So I replaced the ignition amp on that side and it seemed to have settled down. Now mind you, the exterior was nearly all sanded off as I was preparing the car for its recently (beautiful ) full strip and respray. What this means I wasnt able to drive it around and see if the problem was really fully solved as in take it out, get fully wanted up, etc. Turns out it wasn't. Now that I have the car back and am driving it there is a stumble at 1/3 throttle or so and it seems to get worse the more the cars stays warm, almost as if the ignition amp gets warm and starts acting up. Does this sound plausible? How can I really test one of these amps beyond replacement. I do have a new one coming but it will be a few days before it arrives.
Anyone have thoughts why this problem would creep up sitting on my lift for that time? Never touched any ignition parts while it sat. Logging with shark tuner and victor to see if we can see obvious issues but nothing so far.
Beyond my amps, what could be the issue? Grounds are shiny clean and stabliant coated.
What could fail while sitting and off?

SeanR

How are all your main engine harness connectors? Temp II/MAF etc?

sydneyman

uh oh. hope my issue wasnt contagious.

soontobered84

Jeff,
Did you replace the amp(s) with bonified Bosch ignition amps? I've heard of some issues with non-Bosch replacements.

Mrmerlin

did you put fresh heat sink paste on the bottom of the amp?
The bigger the glob the better the job

jeff spahn

no. generic. on my list to try bosch

jeff spahn

funny you say that. we were missing a tube and had to split what little was in the one tube between the two amps. Sean, Victor and I were discussing that as a possibility. Got some apparently high end computer chip convective gel on the way. gonna slather them up good and see if that does it.

WallyP

Probably not your problem, but the battery connections can always use a good cleaning...

jeff spahn

It is definately temperature related. When the car is cold, yet off the start up map there is no hesitation or sputter. As you drive longer and longer and the "whatever" heat soaks, it gets progressively worse. I have two new bosch amps overnighted to me and will try them tomorrow. Seems to point this way. Slather them with heat goo and see if this solves it.

If not, I am still looking for options.

Battery connections are shiny clean. Ground strap is new.

Tom in Austin

Those amps are goofy things ... I tried generic aftermarket versions, ran perfectly at startup but started acting really weird when warmed up. Been on true OEM Bosch ever since ...

dr bob

The 'more is better' on heat-sink paste myth is, well, um, a myth. the paste is used to take up the space between the heat source and the sink. Less is best, so long as there's a continuous path. With the ignition amps there's not so much worry, as they screw down handily and squeeze out what won't fit.

Watching 'techs' put giant globs of paste and then depend on springs to secure a CPU heat sink and fan... It's hard to watch. They then suggest it's working fine because the fans are running faster. Cue the gray rabbit voice-- "Whadda maroon!"

Jeff--

Check the coils. Heat is the enemy of coils. Heat is used to cure paint.

Verify the ground jumpers from the cam covers to the coil brackets. Thes are generally just to help manage noise, but may help solve stupid coil symptoms.

As always, verify the itegrity and routing of ignition wiring. With your four-cylinder symptom, be sure to check the coil wires. Consider the possibility of sanding dust and related crud in the ignition wire boots and the coil towers. You may decide to carefully remove the wires, wash them (!!) gently in a pan with a little Dawn dishwashing detergent, dry them completely and reinstall. That gets rid of all the oil deposits from underhood fumes, deposits from the road, sanding dust, crud, etc. All stuff the wires hate.

Replace the EZK relay if you haven't already. It's the third relay in the JB 'relay-relay-relay' mantra, after LH and Fuel Pump relays. Even though it's third, it still needs attention.

Verify that temp sensor II in the water bridge is connected well and working. Ground integrity is essential there, as it is with everything on the engine.

jeff spahn

So I solved the issue. The coils were original, replaced them with Bosch coils. I also replaced the coil wires while there. Replaced the ignition amps with Bosch amps. Pitched the generic ones in the bin.
Runs smooth now. No hesitation at all.

928 DesMoines

Good deal. Glad it worked out. Just thought I would chime in on the end of this.
My car had one bad amp (An original), so I swapped them both out with HUCO amps (made in Germany). The car started running on all cylinders, but it seemed to run like an old dog.

So, I went and bought Bosch AMPs. Put them in and the car was running great, back to normal. I was suprised that this was real. But first hand, it is real.

I didn't toss the Huco amps, but doubt I will ever use them.

PorKen

I had trouble with the HÜCO/Hitachi amps when using non-resistor plugs. The aluminum backed Huecos could not handle the RFI or something. Odd idle and would not rev over 3000 IIRC.

https://rennlist.com/forums/928-foru...ion-units.html

dr bob

Frame them and hang them on the garage wall. Add a note telling what they are and why they are there.

FWIW, I'd have long ago run out of wall space if I framed and tried to explain every stupid purchase that added no value. Some of this stuff might actually suck value out of the process, since one is easily tempted to cross off those parts as possible causes; after all, they were replaced with new stuff!


I often wish I was actually as smart as I thought I was.