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1993 940 non-turbo b230f, Regina system, wagon. 170ish thousand miles.. mint condition.
Hello All,
The following is part of an email correspondence with another brick head who was trying to help me brainstorm my hesitation problem. For those who have followed my posts for the last couple of years, it should be pretty self explanatory, and for those who are new, any thoughts are welcome.
Also, I had a "no hot soak crank/start" issue a while back which I thought I had resolved by permanently bypassing the RSR, but recently although not since then, I did have this symptom again even with the bypass in place. I haven't really looked into this yet as it seems to be behaving, but perhaps it is related to the hesitation issue.
It is a long read, but hope some of you have the patience to follow my thinking...
So here is the latest..
Hesitation on acceleration issue and my new AC (Air Conditioning) theory:
The odd thing about the hesitation on acceleration symptom is that it "almost" as in 99% of the time does not occur when the brick is running with the AC on. No matter what the outside temp is or how much stop and go hot or cold driving. I have pondered this unusual part of the equation and it did not trigger any comments on the brickboard yet. Since there has not been any instance of "stalling" or complete "dropped/absent" voltage somewhere in the engine, causing a ODB code, when this happens, I can only think that it is temporary incorrect voltage somewhere that is due to a overheated component.
The part of the theory where the AC fits in is explained below.
Not sure about this part :
I'm not entirely knowledgeable in the Regina/Rex-I control protocols and the "Green Book" does not really go into too much detail about the effects of the AC system on engine management, however, there is a small section on how to adjust the idle to compensate for AC/compressor operation. It involves hooking up a hand vacuum pump to the throttle body and adjust the idle according to the amount of "increase" idle speed to compensate for the extra load put on the engine to run the compressor. I don't know if there is a switch somewhere (maybe one of those 3 switches on the front bottom of the condenser?) that tells the ECU to "enrich" the fuel mix that is outside of the Lambda O2 sensor loop temporarily to keep the engine cool and give the block more fuel to run the higher idle etc. during AC operation. If it does, there is no mention of it anywhere in any book or forum that I have found.
The part I do know :
When the AC is engaged, the electric radiator/condenser fan is triggered to run continuously while in operation. Usually, the fan cycles on and off based on input/output voltage based on the thermal sensor switch in the radiator in combination with the readings from ECT sensor. Because it is not on all the time, the engine can get heat soaked quickly especially in "stop and go" traffic where there is little natural airflow coming through from the cars movement. So my idea is whatever is heating up to point where there is this intermittent absent/incorrect signal going to the ECU, or allowing a moment of "lean" mix that causes the hesitation , it has to reach some critical temp and it is apparently cooled by the engine bay electrical fan. Since the ECU and REX control are inside the cab, I know the heat is not affecting it directly unless there is a ground pin that has so much resistance its heating up but I think that's just a bit too far fetched.
Because the symptom almost exclusively (maybe a slight hesitation once under extreme heat conditions) absent when the AC is running and the relays are hot to the touch inside the cab but no stalling or fuel relay failure, also the board itself is mint and all the connectors underneath are solid (when I replaced the Heater Core, I pulled out the board and checked it out) I am pretty confident that it is not anything inside the cab.
So, this leads me to a new idea : whatever is heating up when the AC is not running is being affectively "cooled" by the fan itself inside the engine bay when the AC is running ? Also, because I don't have any symptom of hesitation while at speed for any duration (like on the highway), this also leads me to think about airflow across the engine bay while at speed helps cool down whatever is being affected.
By the way, the actual wire harness in the engine bay is in mint condition and wherever I peeled back the loom to check suspicious looking wire, the wires are as if they came right off the factory floor.
So I have been thinking about the airflow coming from the fan. it pretty much comes in straight across the block and maybe on its sides and below with limited airflow across the top in all likelihood. The little flaps that allow natural airflow in are on the right side of the facing block.
Left Side of block:
1. The distributer cap and wires are mint condition with (silicone jacketed Kingsborne wires with heat protective boots to protect from the exhaust mani) Kingsborne coil wire is same. Hesitation was the same with Bougicord OEM anyway so I don't think its the wires.
2. Plugs are copper NGK with correct gap and never any sign of heat or problems.
3. Battery, brand new, no voltage problems (even when no hot start symptom) and all cables and connectors are solid and mint.
4. RSR – bypassed so it can't be a factor no matter what the heat level.
5. O2 sensor (connector only) no 2-3-2 and I have voltmeter checked it several times over the years.. no problems.
Top of the block:
1. injectors and their ground wires. cleaned them and inspected them several times , seem ok but may one or more are heating up and losing there solid connection ?
2. FPR valve - replaced with new one when I thought it may have been the problem with fuel pressure, fuel is constantly running through it so it stays pretty cool even in the hottest conditions.
3. RPM sensor toward the back, brand new and its connector is solid although it is high up at the back of the bay by the firewall, maybe heat affected...but never any Tach weirdness to indicate a problem.
Right side of Block and probably the most affected by the fan blowing air by:
1. IAC , could be heating up and its connection ? It could stand to reason that the motor inside the IAC malfunctions during overheating and when coming off idle is wide open, causing a large vacuum leak type scenario..?
2. ECT sensor on the block, could be heating up and its connection ?
3. TPS on the throttle body, I had an idea to hook up my digital voltmeter (on the continuity setting) inline on the wire and see if it drops(absent) voltage when it hesitates since it is a on/off switch, also could be heating up and its connection ?
4. Map sensor, replaced with correct Bar new part, did not affect hesitation.
5. Knock sensor, affects timing , also swapped out with new with correct torque.
6. Ignition Coil, could be heating up and its connection ?
The "no crank, hot no start" problem : Related ? I had originally thought the RSR was the problem but after it failed to crank/start even with a permanent bypass of the RSR installed, I had to retract my conclusion.
So the starter and alternator are on the right side as well but the charging system is fine and the starter wouldn't relate to the hesitation problem.
Although.....
Also, if an engine ground wire somewhere, (although I have been persistent about cleaning and making sure all wires are solid in the engine bay) it could cause a secondary related cause for the ignition coil itself over heating (as in too much resistance). This would also explain the starter not operating correctly. But I'm trying to trouble shoot two separate (if not related) problems.
So far my best guesses are :
No start problem -
1. Bad ground wire somewhere, starter overheating, bad wire/connection to starter solenoid f rom alternator
2. Neutral Position Switch inside the cab, you never know.
3. keyed ignition switch on the dash.. again who knows.
Hesitation problem -
1. one or more right side engine block sensors affected by heat, giving incorrect signals to ECU.
2. TPS malfunction when overheated, injectors not fired when supposed to.. coming off idle.
3. ignition coil - overheating due to bad ground/connection, and/or its mounting and location in the engine bay, not transferring heat away , initial winding not providing voltage to coil wire when needed.
4. voltage dropping to injectors somehow, somewhere..
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