harley71105

88 RX7 SA NON TURBO
Ok...I'm going to condense this down the best I can. I'm getting hard to start. Once started (does not flood seems as if fuel starved) I have to keep it at 1200 plus rpm or she dies. Runs smooth up thru 4,000 rpm UNTIL she warms up then the backfire with rough idle returns.
1. Rechecked Compression at 79 front and 81 rear.
2. New Fuel Pump
3. Switched out BAC Valve (Idle Air Control Valve depending on who you ask)
4. Switched out Fuel Pressure Regulator
5. Had already installed new plugs and wires a few months before this started (didn't really need them)
6. Swapped out leading and trailing coil units
(I have accumulated a lot of spare parts as I've had the car 18 years)

There have been no modifications on this car and she is bare bones original.

I cannot think and have not had experience in what to check next until I look at it more and just try some things. I really think that it is somehow getting fuel starved since I cannot seem to flood it and after a lot of cranking on the times it dont start (sometimes it does right off the bat) I can pull a plug and it is dry.

This is all I can think of at the moment and I am offering $50 to the first member that gets me on the right track to repair short of having to take it to the dealer. They know me well here because I had an engine replaced ten years ago in my other 88 SA Non Turbo. They are really good and trustworthy but I would rather us figure this out if yall know what I mean...LOL

Akagis_white_comet

iTrader: (4)

Here's a semi-short checklist of what seems to ring true in my mind on this

1. Compression seems a little on the low side. What method did you use to check it? A piston compression gauge with the relief valve held open? If so, those numbers wouldn't surprise me for an engine that has had some miles put on it. My old S4NA engine did roughly 80 on both rotors, 32psi per rotor face, when tested with a piston compression gauge right before I sold it at 99k. Before being pulled in favor of the 20B-REW, it would start easily with no fuss. Coolant seals were another story... For now, having even compression on all rotor faces is the main thing. If yours is even, we can rule out internal issues.

2. When you replaced the fuel pump, did you test the new one before installing it? Apply 12v+ and Ground from the battery to the pump's terminals and you'll hear it run. If it doesn't immediate spring to life, it's shot. Hotwiring a pump for 2-3 seconds is fine and won't damage it from heat. Be sure to check the voltage at the pump connector too. Voltage drop means it can't pump as well as it needs to.

3. BAC (Bypass Air Control Valve) is what allows air to bypass the throttle body to offset mechanical loads on the engine due to Power Steering, A/C, etc. Test in the same manner as the fuel pump. It should immediately click open, then shut as soon as either power or ground is removed.

4. Fuel Pressure Regulator is most likely fine. I would suspect fuel flow issues before this.

5. New spark plugs & wires are always useful in diagnosing issues. However, old plugs can be cleaned with a wire brush and reused if they have sufficient electrode left.

6. Needing new ignition coils seems unlikely as the FC ones are quite hearty AFAIK. During the winter months before the 20B conversion, my 13B would sometimes be a bit stubborn to start. What worked was to repeatedly prime the engine, artificially increasing its compression. After 3-4 key-on/key-off cycles, the engine would start no matter how cold it was. This shows how powerful the ignition coils really are after 20 years of use.

My gut feeling is saying this is an electrical/wiring issue and I'm leaning towards spotty grounds, specifically the ECU ground. As Aaron Cake says, the infamous 3800rpm hesitation is often due to a poor ECU Ground. Here is a link to Aaron Cake's Grounding FAQ: Proper RX-7 Grounding Procedures

In short, if the ECU is not grounded well, the injectors cannot operate nor can the ignition coils fire as both receive ground signals from the ECU when it needs inject fuel or fire the coils. The ground path for the ECU is as follows:

ECU---Shortblock under UIM---Starter Body---Main Chassis Ground (Driver's side inner fender)---Battery Negative Terminal

What links the Starter Body, Main Chassis Ground and Negative Battery Terminal together is an odd 3-terminal battery cable. Personally, I have found it better to just replace this with two 24" 4awg cables and some Marine Battery Terminals. If you are replacing the negative cables, doing the same for the positive cable(s) would be a good idea too. Battery Positive to Starter is 48", Battery Positive to Alternator is about 30" and you can crimp a fresh ring terminal on for the fuse box. Since there would be 3 cables meeting at the positive terminal, this is why I recommend Marine Battery Terminals, the kind with wing nuts on them. Other than this, follow Aaron Cake's guide to the letter.

After ensuring you have good grounds, what I would do is start doing continuity tests between the ECU and its targets, beginning with the fuel injectors. 0.07 ohms of resistance or less on your digital multimeter ($5 at Harbor Freight) is GOOD, greater than 0.1 ohms is bad and should be written down on a notepad as you go through the harness.

Hope this helps

harley71105

I appreciate your in depth appraisal of my problem. The more I learn about these Rx7's the more I realize that I don't know near enough. I have been driving them exclusively since I purchased my first RX in 1984 which was a 1982 model. I was a traveling salesman for 30 some odd years and I put over 500,000 miles on that 1982 in a ten year period, no kidding. I sold it locally and explained to the man that the odometer was correct. I saw him off and on around town for three years. My present RX has 168,000 miles. I own a cab business and otherwise drive a Crown Victoria Police Interceptor.

It will take a few days to affect these grounding repairs and I will let you know what happens. At this point you are in the running for the $$$. Thanks again.

harley71105

Ok..the past few days I did all the grounds under the hood except for the one under the Intake. About ten years ago I did clean that one while I was redoing some fuel lines so hopefully it won't turn out to be that one. First go around I got a stronger start and the bells that sound when you put in the key started up and they havent for a while. It ran ok for a little longer but still would die without throttle and some small backfire.
I did get under her today and noticed that when I replaced my starter last year I somehow left the ground undone. It did however work for all that time since until here just recently. I'm halfway done with that as in the next day or so I'm going to run a new ground entirely since I'm having trouble tracing the Starter Ground.

satch

iTrader: (1)

Starter ground begins at the negative battery cable and then to the driver's fender and then to the starter.

harley71105

Thank You.

Akagis_white_comet

iTrader: (4)

Satch is correct in regard to the starter ground/negative battery cable. Its total length is approximately 48" long with the fender terminal dead center. As the middle terminal and exposed cable surrounding it is pretty much left open to the elements, I have found it beneficial to just replace it entirely with a 24" cable from battery negative to fender ground and another 24" cable from fender ground to starter mounting bolt (main engine ground).

With properly made cables (Heat Shrink!), this leaves zero exposed wire and improves the ground path for everything attached to the engine.

As for the ECU ground under the UIM (ring terminal with two black wires), one thing Aaron Cake doesn't mention is that since this one is often a pain to access, splicing in a redundant ground directly on the car's sheetmetal would probably be a good idea. I'm not one for adding extra ground wires frivolously, but one as important as this is worthy of some intelligently-designed redundancy due to placement of the original.

He recommends doing this for the Map Sensor's ground, so doing it for the ECU as well means that every sensor except for the O2 sensor on the car will have a redundant ground.

One place where you might consider grounding these to is the passenger side inner fender. There are several M6x1.0 and M8x1.25 threaded holes covered with plastic fir tree trim clips, exactly like on the driver's side near the main ground. May take some ingenuity to make it look good and be sufficiently protected from exhaust heat, but I'll leave that up to you.