1993 Hyundai Excel dies when giving throttle

Maintenance/Repairs
1

Back story:

Just acquired this car with 130k. The previous owner owned this car all throughout college and dumped an obscene amount of money into it for what it is. I have a stack of receipts and work orders several inches high that came with the car, with every single oil change nut and bolt this guy bought for it. It was sitting in his driveway for several months because couldn’t get the thing running…it just stopped out of nowhere. He decided to part with it since he is working full time and has a wife and child to support.

The work that has been done from previous owner. All of this has been done in the past 2-4 years:

Fuel system: gas tank drained and cleaned out, fuel pump, fuel filter, fuel pressure regulator, new injectors.
Ignition: distributor, distributor cap & rotor, spark plugs, spark plug wires. Coil is still original.
Electrical: O2 sensor, ECM coolant temperature sensor, ECM (mom and pop shop replaced it with a junkyard unit from a different car, not 100% compatible with a 93 Excel).
Engine: cylinder head rebuild, timing belt and components replaced.
Misc: thermostat, coolant hoses, PCV valve, all vacuum hoses replaced, brand new exhaust from the converter back, converter has been hollowed out, new struts/shocks, tons of front end work, tires, MAF cleaned with appropriate cleaner, etc.

Here’s what I have done:
I replaced the throttle position sensor, replaced the air filter (it had a K&N that did not fit right), replaced the idle control servo, and also replaced the ECM with the correct one. Also replaced fuel filter, all fusible links, and the relay box for the fuel system. I’ve tested the TPS circuit extensively and it checks out both on the sensor side and ECM side. Also there is a TSB for a bad ground which would cause the TPS and motor position sensor circuits to mess up, but I have already checked them and they were fine.

TLDR;
Previous owner replaced a ton of parts, I can get the car to start and idle without much incident but as soon as you give it any throttle it gurgles pops and dies.

2

How long ago was the fuel pump/filter replaced?

Tester

3

The filter was replaced by the P/O about 2-3 years ago. The pump was done at the same time. I actually replaced the fuel filter again yesterday, and I have a new Denso pump for the car that I practically got for free just in case.

4

You want to test the fuel pump for proper pressure and volume.

If either of those is below spec, the engine will fall on it’s face when power is asked from it.

Tester

5

Heck, you might as well throw a new coil in it.

6

I don’t believe there is a test port on the engine. You have to get a special adapter that threads into the fuel filter, and I have yet to find one. Yeah the coil is pretty much the only ignition related component that hasn’t been replaced so far.

7

Here’s what I’d do

First, read out any stored or pending diagnostic codes in the ECM memory. This car is probably OBD I, but the codes can still be read out. Do this first, whether or not the check engine light is on or off.

Next, check the entire vacuum system including all lines and vacuum operated devices for vacuum leaks.

Next is to check the fuel pressure. Does the fuel pressure regulator have any gasoline in the vacuum port? If so, replace it. If the fpr looks ok, ask your shop to rig up a fuel pressure gauge and read it both at idle and when you stomp on the gas. When you stomp on the gas the fuel pressure shouldn’t drop much if at all.

Finally, some throttle position sensors of this era didn’t sense the degrees of throttle opening, just if the throttle was closed (idle), wide open, or somewhere in between. There were only three outputs in other words. Check yours, if it is like that, verify with a dvm that all three positions are working and calibrated to operate at the correct throttle opening.

Beyond that, well you are looking at the ignition system, compression, valve timing, etc. I might be inclined to temporaily disconnect the exhaust pipe so there is a clear path to the outside for exhaust gasses to see if that fixes the problem. Very loud experiment, but might provide a clue as to what is wrong.

8

Thanks for the reply!

There was no CEL and no passive codes were stored the other day but I haven’t checked it since. I will do that tomorrow to see if anything else comes up.

There actually isn’t much in the form of vacuum lines on this engine, thankfully. They were all replaced by the previous owner as well and I can verify no issues with them actually leaking.

FPR is brand new but I will check the vacuum line just in case.

The TPS on this car outputs voltage from any position. Idle is around .35 to .45 volts, and slowly raises until maxing out around 4.8 to 5 volts at wide open throttle. There were no dead spots at all.

The converter was gutted by the previous owner.

9

“ECM (mom and pop shop replaced it with a junkyard unit from a different car, not 100% compatible with a 93 Excel).”

Can you describe the differences? I’m thinking that if the replacement ECM isn’t mapped the same as the correct one it might be starving the engine when you hit the throttle. Can you locate a proper ECM through a boneyard?

I didn’t see a new MAP sensor in your list. If your engine has one, that may not be responding properly to the sudden change in manifold pressure.

I also didn’t see in your list any testing of the ignition timing. Is it properly advancing?
Is this a distributor based system?

10

The ECM that was in the car was from a Dodge 3000GT. I have since replaced it with the proper OEM one. (I have this issue posted on multiple sites, forgot to add the new ECM bit here.) Car doesn’t have a MAP sensor. The timing components and distributor were all replaced and timing was checked and set both times…I can only assume it’s still in spec. The car runs smooth as silk when idling.

11

Also I should mention that this car has the 1.5L Mitsubishi engine that is found in several different makes, hence having a used ECM out of a Dodge.

12

And if you barely…and I mean BARELY give it gas, it revs up perfectly fine. But any more than a slight press on the pedal and it dies.